Diffusion resistance layer for analyte sensors

Abstract

To disclose a device for determining an analyte concentration (e.g., glucose).SOLUTION: A device comprises a sensor configured to generate a signal associated with a concentration of an analyte and a sensing membrane located over the sensor. The sensing membrane comprises an enzyme layer, where the enzyme layer comprises an enzyme and polymer including polyurethane and / or polyurea segments and one or more zwitterionic repeating units. The enzyme layer protects the enzyme and prevents it from leaching from the sensing membrane into a host or deactivating.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] INCORPORATION BY REFERENCE OF RELATED APPLICATIONS Any priority claim identified in the Application Data Sheet, or any correction thereto, is incorporated herein by reference under 37 CFR § 1.57. This application claims the benefit of U.S. Provisional Application No. 62 / 273,155, filed December 30, 2015, U.S. Provisional Application No. 62 / 273,142, filed December 30, 2015, and U.S. Provisional Application No. 62 / 273,219, filed December 30, 2015. Each of the foregoing applications is incorporated herein by reference in its entirety, and each is hereby expressly made a part of this specification.

[0002] The subject matter disclosed herein relates to devices for measuring biological analytes in a host, and components of such devices. [Background technology]

[0003] Electrochemical sensors are useful for determining the presence or concentration of biological analytes, such as blood glucose. Such sensors are useful, for example, in monitoring glucose in diabetic patients and lactate during critical care events. A variety of intravascular, transcutaneous, and implantable sensors have been developed to continuously detect and quantify blood analytes, such as blood glucose levels.

[0004] In some analyte sensors, there is a membrane layer or domain that is primarily responsible for limiting the diffusion of the analyte to the sensor. The function of this so-called diffusion resistance layer can be important when the analyte of interest is present in the patient in an amount that may exceed the sensitivity of the sensor. For example, there is a molar excess of glucose compared to the amount of oxygen in the body. Thus, for every free oxygen molecule in the extracellular fluid, there are typically more than 100 glucose molecules (see Updike et al., Diabetes Care 5:207-21 (1982)). However, immobilized enzyme-based glucose sensors that use oxygen as a co-reactant are preferably supplied with oxygen in a non-rate-limiting excess so that the sensor responds linearly to changes in glucose concentration while not responding to changes in oxygen concentration. Specifically, when the glucose monitoring reaction is oxygen-limited, linearity is not achieved above a minimum concentration of glucose. Without a semi-permeable membrane located over the enzyme domain to control the flux of glucose and oxygen, a linear response to glucose levels can only be obtained at glucose concentrations up to about 40 mg / dL. However, in a clinical setting, a linear response to glucose levels of at least up to about 400 mg / dL is desirable.

[0005] Some diffusion resistance layers suffer from changes in permeability to analytes due to microstructural changes, phase separation, decomposition, and interference from external molecules. These changes can affect sensor sensitivity and therefore lead to changes in sensor output at the same analyte concentration over time, a phenomenon known as "drift". This confounds the development of robust algorithms, as they require sensor "drift" correction. Thus, there is a need for engineered semi-permeable diffusion resistance layers that include polymers that can provide a structurally stable matrix throughout which an analyte permeable phase resides and electrochemical sensors are equipped with such membranes. The compositions, methods, and devices disclosed herein address these and other needs. Summary of the Invention [Problem to be solved by the invention]

[0006] In accordance with the objectives of the disclosed materials and methods, as embodied and broadly described herein, the disclosed subject matter relates in one aspect to methods of making and using compounds, compositions, and devices containing the compounds and compositions. [Means for solving the problem]

[0007] In a first aspect, a device for determining an analyte concentration (e.g., glucose) is provided, the device comprising a sensor configured to generate a signal associated with the concentration of the analyte and a sensing membrane located on the sensor. In a particular embodiment, a device for measuring an analyte concentration is disclosed herein, the device comprising a sensor configured to generate a signal associated with the concentration of the analyte and a sensing membrane located on the sensor, the sensing membrane comprising a diffusion-resistant layer comprising a base polymer having a minimum glass transition temperature measured using ASTM D3418 greater than -50°C and a maximum tensile strength measured by ASTM D1708 greater than 6000 psi. For example, the glass transition temperature of the base polymer may be greater than 0°C and / or the maximum tensile strength of the base polymer may be greater than 8250 psi.

[0008] In certain examples, the base polymer may be a segmented block copolymer. For example, the base polymer may include polyurethane and / or polyurea segments and one or more polycarbonate or polyester segments. In other examples, the base polymer may be a polyurethane copolymer selected from polyether-urethane-urea, polycarbonate-urethane, polyether-urethane, polyester-urethane, and / or copolymers thereof, so long as the minimum glass transition temperature is greater than -50°C. In other examples, the base polymer includes a polymer selected from epoxy, polyolefin, polyoxymethylene, polyether, polyacrylic acid, polymethacrylic acid, polyester, polycarbonate, polyamide, poly(ether ketone), poly(ether imide), and / or copolymers thereof, so long as the minimum glass transition temperature is greater than -50°C. In yet other examples, the base polymer may be substantially free of silicone. In a further example, the diffusion-resistant layer may further include a hydrophilic polymer. For example, the hydrophilic polymer may be selected from polyvinyl alcohol, polyethylene glycol, polyacrylamide, polyacetate, polyethylene oxide, polyethylene amine, polyvinylpyrrolidone (PVP), polyoxazoline (POX), and copolymers and / or mixtures thereof. In other examples, the hydrophilic polymer may be blended with the base polymer or may be covalently bonded to the base polymer. In yet other examples, the base polymer or hydrophilic polymer may include one crosslinker or several crosslinkers, the crosslinkers including polymers or oligomers selected from polyfunctional isocyanates, polyfunctional aziridines, polyfunctional carbodiimides. In other examples, the diffusion-resistant layer may include a blend of polycarbonate-urethane base polymer and polyvinylpyrrolidone. The diffusion-resistant layer may be 0.01 μm to about 250 μm thick.

[0009] In certain embodiments, a sensor is disclosed that has a drift of 10% or less over a 10 day period. The sensor may include electrodes, and the device may be configured to continuously measure an analyte concentration, such as glucose.

[0010] In another aspect, a device for measuring an analyte concentration is disclosed, the device comprising: a sensor configured to generate a signal related to the concentration of the analyte; and a sensing membrane located on the sensor, wherein the sensing membrane includes a diffusion resistance layer, and the sensor has less than 10% drift in the signal over a 10 day period.

[0011] In yet another aspect, a device for measuring an analyte concentration is disclosed, the device comprising: a transcutaneous sensor configured to generate a signal associated with the concentration of the analyte; and a sensing membrane located on the sensor, the sensing membrane comprising a diffusion resistant layer, the diffusion resistant layer comprising a polyurethane comprising a block copolymer and being substantially free of silicone.

[0012] In all of the devices disclosed herein, they can be configured for continuous measurement of analyte concentration.

[0013] Additional advantages will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the following aspects. The advantages will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive.

[0014] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several aspects described below. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram of a continuous analyte sensor system attached to a host and in communication with other devices. [Figure 2A] 1A-1D are cross-sectional views of sensors illustrating various embodiments of membrane systems. [Figure 2B] 1A-1D are cross-sectional views of sensors illustrating various embodiments of membrane systems. [Figure 2C]1A-1D are cross-sectional views of sensors illustrating various embodiments of membrane systems. [Figure 3A] FIG. 2 is a side schematic diagram illustrating an in vivo portion of a continuous analyte sensor in one embodiment. [Figure 3B] FIG. 2 is a perspective schematic diagram illustrating an in vivo portion of a continuous analyte sensor in one embodiment. [Figure 3C] FIG. 2 is a side schematic diagram illustrating an in vivo portion of a continuous analyte sensor in one embodiment. [Figure 3D] FIG. 2 is a cross-sectional / side schematic diagram illustrating an in vivo portion of a continuous analyte sensor in one embodiment. [Figure 4] 1 is a graph showing drift testing of sensors constructed with RL (resistive layer) films with silicone (thin lines) and without silicone (thick lines). [Diagram 5] 1 is a plot of a differential scanning calorimetry heating scan performed on a TA Instrument's Q2000 DSC using an aluminum sample pan on a resistive layer polyurethane polymer sample. [Figure 6A] 1 is a pair of graphs showing the tensile strength and puncture resistance of RL (resistance layer) membranes with and without silicone. Tensile strength data was obtained on membranes that were not blended with a hydrophilic polymer such as PVP. Puncture resistance data was obtained on wet membranes blended with PVP. [Figure 6B] 1 is a pair of graphs showing the tensile strength and puncture resistance of RL (resistance layer) membranes with and without silicone. Tensile strength data was obtained on membranes that were not blended with a hydrophilic polymer such as PVP. Puncture resistance data was obtained on wet membranes blended with PVP. [Figure 7] 4 shows the results of an in vivo sensor stability study (pig model). [Figure 8] FIG. 8 shows images captured by scanning electron microscopy of sensors from the in vivo sensor stability study described in FIG. [Figure 9A]1 is a pair of graphs showing sensor data in a porcine model using a sensor with a RL (resistive layer) containing silicone and a sensor without silicone in the RL. [Figure 9B] 1 is a pair of graphs showing sensor data in a porcine model using a sensor with a RL (resistive layer) containing silicone and a sensor without silicone in the RL. [Figure 10] 1 is a graph showing drift testing of sensors constructed with a silicone-free RL (resistive layer) film that was submerged in water prior to curing. The control represents a sensor constructed with a silicone-containing RL cured at standard humidity. [Figure 11A] FIG. 1 is a schematic diagram of a portion of one embodiment of an interference domain comprising multiple polycation and polyanion layers. [Figure 11B] 11A illustrates one embodiment of a layer-by-layer method using layer-by-layer adsorption of polycations and polyanions to create the structure illustrated in FIG. 11A. [Figure 12] FIG. 1 is a schematic diagram illustrating one particular embodiment of a membrane layer polymer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The methods, compositions, and devices described herein may be understood more readily by reference to the following detailed description of certain aspects of the disclosed subject matter and the examples and figures included therein.

[0017] Before the methods, compositions, and devices are disclosed and described, it is to be understood that the following aspects are not limited to particular synthetic methods or to particular reagents, and as such, can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to be limiting.

[0018] Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed subject matter pertains. The references disclosed are also individually and specifically incorporated by reference into this specification for the material contained therein that is discussed in the sentence in which the reference is relied upon. definition

[0019] In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings.

[0020] As used herein, the term "about" is intended to qualify the numerical value it modifies and indicates such value as being variable within a margin of error. When a specific margin of error, such as a standard deviation for the average value shown in a chart or table of data, is not recited, the term "about" should be understood to mean a range encompassing the recited value, taking into account significant digits, as well as a range encompassed by rounding up or down to that number.

[0021] As used herein, the term "analyte" is a broad term given its ordinary and customary meaning to those of skill in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, a substance or chemical constituent in a biological fluid (e.g., blood, interstitial fluid, cerebrospinal fluid, lymphatic fluid, urine, sweat, saliva, etc.) that may be analyzed. Analytes may include naturally occurring substances, man-made substances, metabolic products, and / or reaction products. In some embodiments, the analyte for measurement by the sensing regions, devices, and methods is glucose. However, other analytes are contemplated as well, including acarboxyprothrombin, acylcarnitines, adenine phosphoribosyltransferase, adenosine deaminase, albumin, α-fetoprotein, amino acid profile (arginine (Krebs cycle), histidine / urocanic acid, homocysteine, phenylalanine / tyrosine, tryptophan), andrenostenedione, antipyrine, arabinitol enantiomers, arginase, benzoylecgonine (cocaine), biotinidase, biopterin, c-reactive protein, carnitine, carnosinase, CD4, ceruloplasmin, chenodeoxycholic acid, chloroquine, cholesterol, cholinesterase, conjugated 1-β hydroxycholic acid, cortisol, creatine kinase, creatine kinase MM isoenzyme, cyclosporin A, d-penicillin, creatine kinase MM isoenzyme, d-penicillin ... Lamin, de-ethylchloroquine, dehydroepiandrosterone sulfate, DNA (acetylation polymorphisms), alcohol dehydrogenase, alpha 1-antitrypsin, cystic fibrosis, Duchenne / Becker muscular dystrophy, analyte-6-phosphate dehydrogenase, hemoglobin A, hemoglobin S, hemoglobin C, hemoglobin D, hemoglobin E, hemoglobin F, D Punjab, beta-thalassemia, hepatitis B virus , HCMV, HIV-1, HTLV-1, Leber's hereditary optic neuropathy, MCAD, RNA, PKU, Plasmodium vivax, sex differentiation, 21-deoxycortisol), desbutylhalofantrine, dihydropteridine reductase, diphtheria / tetanus antitoxin, erythrocyte arginase, erythrocyte protoporphyrin, esterase D, fatty acids / acylglycines, free β-human chorionic gonadotropin, free erythrocyte porphyrin,Free thyroxine (FT4), free tri-iodothyronine (FT3), fumarylacetoacetase, galactose / gal-1-phosphate, galactose-1-phosphate uridyltransferase, gentamicin, analyte-6-phosphate dehydrogenase, glutathione, glutathione peroxidase, glycocholate, glycosylated hemoglobin, halofantrine, hemoglobin variants, hexosaminidase A, human erythrocyte carbonic anhydrase I, 17-α-hydroxyprogesterone, hypoxanthine phosphoribosyltransferase, immunoreactive trypsin, lactate, Lead, lipoproteins ((a), B / A-1, β), lysozyme, mefloquine, netilmicin, phenobarbitone, phenytoin, phytanic acid / pristanic acid, progesterone, prolactin, prolidase, purine nucleoside phosphorylase, kinin, inverted tri-iodothyronine (rT3), selenium, serum pancreatic lipase, sisomicin, somatomedin C, specific antibodies (adenovirus, antinuclear antibody, anti-zeta antibody, arbovirus, pseudorabies virus, dengue virus, dracunculia, tapeworm, cecum, entamoeba histolytica, enterovirus, Giardia lamblia (giardia duodenalisa, Helicobacter pylori, Hepatitis B virus, Herpes virus, HIV-1, IgE (atopic disease), Influenza virus, Leishmania donovani, Leptospira, Measles / Mumps / Rubella, Mycobacterium leprae, Mycoplasma pneumoniae, Myoglobin, Onchocerca volvulus, Parainfluenza virus, Plasmodium falciparum, Poliovirus, Pseudomonas aeruginosa, Respiratory syncytial virus, Rickettsia (scrub typhus), Schistosoma mansoni, Toxoplasma gondii, Trepenoma pallidium, Trypanosoma cruzi / Langer, Vesicular stomatitis virus virus), Wuchereria bancrofti, Yellow fever virus), specific antigens (Hepatitis B virus, HIV-1), succinylacetone, sulfadoxine, theophylline, thyrotropin (TSH), thyroxine (T4), thyroxine-binding globulin, trace elements, transferrin, UDP-galactose-4-epimerase, urea, uroporphyrinogen I synthase, vitamin A, leukocytes, and zinc protoporphyrin.The analytes may be introduced into the body or may be exogenous, such as, but not limited to, contrast agents for diagnostic imaging, radioisotopes, chemical agents, fluorocarbon-based artificial blood, or drugs or pharmaceutical compositions, such as insulin, ethanol, cannabis (marijuana, tetrahydrocannabinol, hashish), inhalants (nitrous oxide, amyl nitrite, butyl nitrite, chlorohydrocarbons, hydrocarbons), cocaine (crack cocaine), stimulants (amphetamines, methamphetamines, Ritalin, Cylert, Preludin, Didrex, PreState, Voranil, Sandrex, Plegine), depressants (barbiturates, methaqualone, psychotropic drugs, etc.), and the like. These include, but are not limited to, tranquilizers (e.g., Valium, Librium, Miltown, Serax, Equanil, Tranxene), hallucinogens (phencyclidine, lysergic acid, mescaline, peyote, psilocybin), narcotics (heroin, codeine, morphine, opium, meperidine, Percocet, Percodan, Tussionex, Fentanyl, Darvon, Talwin, Lomotil), designer drugs (fentanyl, meperidine, amphetamine, methamphetamine, and analogs of phencyclidine, e.g., Ecstasy), anabolic steroids, and nicotine. Metabolites of drugs and pharmaceutical compositions may also be contemplated as analytes. Analytes such as neurochemicals and other chemicals produced in the body, such as ascorbic acid, uric acid, dopamine, noradrenaline, 3-methoxytyramine (3MT), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxytryptamine (5HT), and 5-hydroxyindoleacetic acid (FHIAA), may also be analyzed.

[0022] As used herein, the term "baseline" is a broad term given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, a component of an analyte sensor signal that is not related to analyte concentration. In one example of a glucose sensor, the baseline is substantially composed of signal contributions due to factors other than glucose (e.g., interfering species, unreacted associated hydrogen peroxide, or other electroactive species with an oxidation potential that overlaps with hydrogen peroxide). In some embodiments where the calibration is defined by solving the equation y=mx+b, the value of b represents the baseline of the signal.

[0023] As used herein, the term "continuous (or continuous) analyte sensing" is intended to be a broad term having its ordinary and customary meaning given to those of skill in the art (and is not intended to be limited to any special or customized meaning), and refers, without limitation, to a period during which monitoring of analyte concentration is performed continuously, continuously, and / or intermittently (but regularly), for example, about every 5-10 minutes.

[0024] As used herein, the term "counts" is a broad term given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, a unit of measurement for a digital signal. In one example, the raw data stream measured in counts is directly related to a voltage (e.g., converted by an A / D converter), which is directly related to the current from the working electrode. In another example, the counter electrode voltage measured in counts is directly related to a voltage.

[0025] As used herein, the term "dipole" or "dipolar compound" is a broad term that is given its ordinary and customary meaning to one of ordinary skill in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, a compound in which a neutral molecule of the compound has positive and negative charges at different positions within the molecule. The positive and negative charges within the molecule can be any non-zero charge up to and including a full unit charge.

[0026] As used herein, the term "distal" is a broad term given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, the spatial relationship between various elements relative to a particular reference point. For example, some embodiments of the sensor include a membrane system having a biointerface domain and an enzyme domain. If the sensor is considered to be the reference point and the biointerface domain is located further away from the sensor than the enzyme domain, then the biointerface domain is more distal to the sensor than the enzyme domain.

[0027] As used herein, the term "domain" is a broad term given its ordinary and customary meaning to those of skill in the art (and is not intended to be limited to any special or customized meaning) and refers to, but is not limited to, a region of a film that may be a uniform or non-uniform gradient (i.e., anisotropic) layer or may be provided as a portion of a film.

[0028] As used herein, the term "electrical potential" is a broad term given its ordinary and customary meaning to those skilled in the art (and is not intended to be limited to any special or customized meaning), and refers to, but is not limited to, the electrical potential difference between two points in a circuit that is responsible for the flow of electric current.

[0029] As used herein, the terms "electrochemically reactive surface" or "electroactive surface" are broad terms and are to be given their ordinary and customary meaning to those skilled in the art (and are not to be limited to any special or customized meaning), and refer to, but are not limited to, the surface of an electrode where an electrochemical reaction occurs. As an example, at the working electrode, H2O2 (hydrogen peroxide) produced by an enzyme-catalyzed reaction of the analyte to be detected reacts, thereby creating a measurable electrical circuit. For example, in the detection of glucose, glucose oxidase produces H2O2 as a by-product. H2O2 reacts with the surface of the working electrode to release two protons (2H + ), 2 electrons (2e - ), and one oxygen molecule (O2), which generates a current that is detected. In the case of the counter electrode, a reducible species, e.g., O2, is reduced at the electrode surface to balance the current generated by the working electrode.

[0030] As used herein, the term "host" is a broad term and refers to its ordinary and customary meaning as provided to those skilled in the art (and is not limited to any special or customized meaning), including, but not limited to, animals (e.g., humans) and plants. In some examples, hosts can include domestic animals (e.g., cats, dogs, etc.), livestock (e.g., cows, horses, pigs, sheep, goats, etc.), laboratory animals (e.g., mice, rabbits, rats, guinea pigs, etc.), and birds. In other examples, hosts can include mammals, such as primates or humans.

[0031] As used herein, the terms "interfering substance" and "interfering species" are broad terms and are given their ordinary and customary meanings to those of skill in the art (and are not limited to any special or customized meanings), and refer to, but are not limited to, effects or species that interfere with the measurement of an analyte of interest in a sensor to produce a signal that does not accurately represent the analyte measurement. In an exemplary electrochemical sensor, an interfering species can include compounds that have an oxidation potential that overlaps with the oxidation potential of the analyte being measured.

[0032] As used herein, the terms "non-zwitterionic dipole" and "non-zwitterionic dipolar compound" are broad terms that are given their ordinary and customary meaning to those of skill in the art (and are not limited to any special or customized meanings) and refer to, but are not limited to, compounds in which a neutral molecule of the compound has positive and negative charges at different positions within the molecule. The positive and negative charges within the molecule may be any non-zero charge, although they are less than a full unit.

[0033] As used herein, the terms "operably connected," "operably connected," and "operably linked" are broad terms and are intended to have their ordinary and customary meanings as given to those of skill in the art (and are not limited to special or customized meanings), and refer to, but are not limited to, one or more components that are connected to another component(s) in a manner that allows for the transmission of a signal between the components. For example, one or more electrodes can be used to detect the amount of analyte in a sample and convert that information into a signal that can then be transmitted to a circuit. In this case, the electrodes are "operably linked" to an electronic circuit.

[0034] The term "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not occur.

[0035] As used herein, the term "polyampholyte polymer" is a broad term and is given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning), and refers to, but is not limited to, a polymer that contains both cationic and anionic groups. Such polymers can be prepared to have an approximately equal number of positive and negative charges, and thus the surface of such polymers can be approximately net neutral in charge. Alternatively, such polymers can be prepared to have either an excess of positive or negative charges, and thus the surface of such polymers can be net positive or negative, respectively.

[0036] As used herein, the term "polyzwitterion" is a broad term and its ordinary and customary meaning is given to those skilled in the art (and is not limited to a special or customized meaning), and refers to, but is not limited to, polymers in which the repeat units of the polymer chain are zwitterionic moieties. Polyzwitterions are also known as polybetaines. Polyzwitterions are a type of polyampholyte polymer because they have both cationic and anionic groups. However, they are unique because both cationic and anionic groups are part of the same repeat unit, which means that polyzwitterions have the same number of cationic and anionic groups, but other polyampholyte polymers may have more of some ionic groups than others. Polyzwitterions also have cationic and anionic groups as part of the repeat unit. Polyampholyte polymers do not have to have cationic groups connected to anionic groups, which can be on different repeat units and thus distributed apart from each other at random intervals, or one ionic group may outnumber the other.

[0037] As used herein, the term "proximal" is a broad term and refers to its ordinary and customary meaning as given to those skilled in the art (and is not limited to a special or customized meaning), and refers to, but is not limited to, the spatial relationship between various elements compared to a particular reference point. For example, some embodiments of the device include a membrane system having a biointerface layer and an enzyme layer. If the sensor is considered to be the reference point and the enzyme layer is located closer to the sensor than the biointerface layer, then the enzyme layer is more proximal to the sensor than the biointerface layer.

[0038] As used herein, the terms "raw data stream" and "data stream" are broad terms and are given their ordinary and customary meanings to those skilled in the art (and are not limited to any special or customized meanings), and refer to, but are not limited to, an analog or digital signal directly related to the measured glucose concentration from a glucose sensor. In one example, the raw data stream is digital data in "counts" (e.g., voltage or amperage) converted from an analog signal by an A / D converter, and represents the glucose concentration. These terms broadly encompass multiple timed data points from a substantially continuous glucose sensor, including individual measurements taken at time intervals ranging from less than one second up to, for example, one, two, or five minutes or more.

[0039] As used herein, the terms "sensing membrane" and "membrane system" are broad terms given their ordinary and customary meaning to those of skill in the art (and are not limited to any special or customized meaning) and refer to, but are not limited to, a permeable or semi-permeable membrane that may include one or more domains or layers, is permeable to oxygen, and is composed of a material several microns or more thick that may or may not be permeable to an analyte of interest. In one example, the sensing membrane or membrane system may include immobilized glucose oxidase enzyme, which allows an electrochemical reaction to occur to measure the concentration of glucose.

[0040] As used herein, the terms "sensing area," "sensor," and "sensing mechanism" are broad terms and are given their ordinary and customary meanings to those of skill in the art (and are not intended to be limited to any special or customized meanings), and refer to, but are not limited to, an area or mechanism of a monitoring device involved in the detection of a particular analyte.

[0041] As used herein, the term "sensitivity" is a broad term given its ordinary and customary meaning to those of skill in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, the amount of signal (e.g., in the form of current and / or voltage) generated by a given amount (unit) of measured analyte. For example, in one embodiment, the sensor has a sensitivity (or slope) of about 1 to about 100 picoamps of current per mg / dL of glucose analyte.

[0042] As used herein, the terms "zwitterion" and "zwitterionic compound" are broad terms and are given their ordinary and customary meaning to those of skill in the art (and are not limited to any special or customized meanings), and refer to, but are not limited to, compounds in which a neutral molecule of the compound has a unit positive charge and a unit negative charge at different positions within the molecule. Such compounds are a type of zwitterionic compound and are sometimes referred to as "inner salts."

[0043] As used herein, the term "zwitterion precursor" or "zwitterionic compound precursor" is a broad term and is intended to have its ordinary and customary meaning as indicated to one of skill in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, any compound that is not itself a zwitterion, but can become a final or transitional zwitterion through chemical reaction. In some embodiments described herein, the device includes a zwitterion precursor that can be converted to a zwitterion prior to in vivo implantation of the device. Alternatively, in some embodiments described herein, the device includes a zwitterion precursor that can be converted to a zwitterion through some chemical reaction that occurs after in vivo implantation of the device. Such reactions are known to those of skill in the art and include ring-opening reactions, addition reactions such as Michael additions, and the like. This method is particularly useful when polymerization of betaine-containing monomers is difficult due to technical difficulties such as the solubility of the betaine monomer to achieve desired physical properties such as molecular weight and mechanical strength. Post-polymerization modification or conversion of the betaine precursor can be a practical method to achieve desired polymer structures and compositions. Examples of such precursors include tertiary amines, quaternary amines, pyridine, and others detailed herein.

[0044] As used herein, the term "zwitterionic derivative" or "zwitterionic compound derivative" is a broad term and is intended to have its ordinary and customary meaning as indicated to one of ordinary skill in the art (and is not limited to any special or customized meaning), and refers to, but is not limited to, any compound that is not itself a zwitterion, but rather is the product of a chemical reaction in which a zwitterion is converted to a non-zwitterion. Such reactions may be reversible, so that under certain conditions, a zwitterionic derivative may act as a zwitterionic precursor. For example, a hydrolyzable betaine ester formed from a zwitterionic betaine is a cationic zwitterionic derivative that can undergo hydrolysis back to a zwitterionic betaine under appropriate conditions.

[0045] As used herein, the following abbreviations apply: Eq and Eqs (equivalents), mEq (milliequivalents), M (mole), mM (millimolar), μM (micromolar), N (normal), mol (mole), mmol (millimolar), μmol (micromolar), nmol (nanomole), g (gram), mg (milligram), μg (microgram), Kg (kilogram), L (liter), mL (milliliter), dL (deciliter), μL (microliter), cm (centimeter), mm (millimeter), μm (micrometer), nm (nanometer), h and hr (hours), min (minutes), s and sec (seconds), °C (degrees Celsius). Sensor Systems

[0046] FIG. 1 is a schematic diagram of a continuous analyte sensor system 100 attached to a host and in communication with a number of other exemplary devices 110-113. The transdermal analyte sensor system is shown comprising an on-skin sensor assembly 600 secured to the skin of the host via a disposable housing (not shown). The system includes a transdermal analyte sensor 200 and an electronics unit (interchangeably referred to as "sensor electronics" or "transmitter") 500 for wirelessly transmitting analyte information to a receiver. In use, a sensing portion of the sensor 200 resides beneath the skin of the host and a contact portion of the sensor 200 is operably connected (e.g., electrically connected) to the electronics unit 500. The electronics unit 500 is engaged with a housing attached to an adhesive patch secured to the skin of the host.

[0047] The on-skin sensor assembly 600 may be attached to the host using an applicator adapted to provide convenient and safe application. Such an applicator may also be used to insert the sensor 200 through the skin of the host. Once the sensor 200 is inserted, the applicator is detached from the sensor assembly.

[0048] In general, the continuous analyte sensor system 100 includes any sensor configuration that provides an output signal indicative of an analyte concentration. The output signal (including sensor data, such as raw data stream, filtered data, smoothed data, and / or otherwise transformed sensor data, for example) is transmitted to a receiver, which may be, for example, a smartphone, a smartwatch, a dedicated device, or the like. In one embodiment, the analyte sensor system 100 includes a transcutaneous glucose sensor, such as that described in U.S. Patent Publication No. US-2011-0027127-A1, the contents of which are incorporated herein by reference in their entirety. In some embodiments, the sensor system 100 includes a continuous glucose sensor, such as a transcutaneous sensor, such as that described in U.S. Patent No. 6,565,509 to Say et al. In another embodiment, the sensor system 100 includes a continuous glucose sensor, such as a subcutaneous sensor, such as that described with reference to U.S. Patent No. 6,579,690 to Bonnecaze et al. or U.S. Patent No. 6,484,046 to Say et al. In another embodiment, the sensor system 100 includes a continuous glucose sensor, such as a subcutaneous sensor, such as that described with reference to U.S. Patent No. 6,512,939 to Colvin et al. In another embodiment, the sensor system 100 includes a continuous glucose sensor, such as an intravascular sensor, such as that described with reference to U.S. Patent No. 6,477,395 to Schulman et al. In another embodiment, the sensor system 100 includes a continuous glucose sensor, such as an intravascular sensor, such as that described with reference to U.S. Patent No. 6,424,847 to Mastrototaro et al. Other signal processing techniques and glucose monitoring system embodiments suitable for use with the embodiments described herein are described in U.S. Patent Publication Nos. US-2005-0203360-A1 and US-2009-0192745-A1, the contents of which are incorporated herein by reference in their entireties. The sensor extends through a housing that maintains the sensor on the skin and is provided in an electronics unit to provide electrical connections between the sensor and the sensor electronics.

[0049] In one embodiment, the sensor is formed from or in the form of a wire. For example, the sensor may include an elongated conductor, such as a bare elongated conductive core (e.g., metal wire), or an elongated conductive core coated with one, two, three, four, five, or more layers of material, each of which may or may not be conductive. The elongated sensor may be long and thin, yet flexible and strong. For example, in some embodiments, the smallest dimension of the elongated conductor is less than about 0.1 inches, less than about 0.075 inches, less than about 0.05 inches, less than about 0.025 inches, less than about 0.01 inches, less than about 0.004 inches, or less than about 0.002 inches. The sensor may have a circular cross section. In some embodiments, the cross section of the elongated conductor may be oval, rectangular, triangular, polygonal, star-shaped, C-shaped, T-shaped, X-shaped, Y-shaped, irregular, etc. In one embodiment, a conductive wire electrode is used as the core. To such clad electrodes, one or two additional conductive layers may be added (e.g., with an intervening insulating layer providing for electrical isolation). The conductive layers may be composed of any suitable material. In certain embodiments, it may be desirable to use a conductive layer that includes conductive particles (i.e., particles of a conductive material) in a polymer or other binder.

[0050] In certain embodiments, the materials used to form the elongated conductors (e.g., stainless steel, titanium, tantalum, platinum, platinum-iridium, iridium, certain polymers, and / or the like) can be strong and rigid to prevent damage. For example, in some embodiments, the ultimate tensile strength of the elongated conductors is about 80 kPsi to about 500 kPsi. In another example, in some embodiments, the Young's modulus of the elongated conductors is about 160 GPa to about 220 GPa. In yet another example, in some embodiments, the yield strength of the elongated conductors is about 60 kPsi to about 2200 kPsi. In some embodiments, the small diameter of the sensor provides (e.g., imparts, allows) flexibility to these materials, and thus to the sensor as a whole. Thus, the sensor can withstand repeated forces exerted on it by the surrounding tissue.

[0051] In addition to providing structural support, resilience, and flexibility, in some embodiments, the core (or components thereof) provides electrical conduction for an electrical signal from the working electrode to the sensor electronics (not shown). In some embodiments, the core comprises a conductive material, such as stainless steel, titanium, tantalum, conductive polymers, and / or the like. However, in other embodiments, the core is formed from a non-conductive material, such as a non-conductive polymer. In still other embodiments, the core comprises multiple layers of material. For example, in one embodiment, the core comprises an inner core and an outer core. In further embodiments, the inner core is formed from a first conductive material and the outer core is formed from a second conductive material. For example, in some embodiments, the first conductive material is stainless steel, titanium, tantalum, conductive polymers, alloys, and / or the like, and the second conductive material is a conductive material selected to provide electrical conduction between the core and the first layer and / or to adhere the first layer to the core (e.g., when the first layer is formed from a material that does not adhere well to the core material). In another embodiment, the core is formed of a non-conductive material (e.g., a non-conductive metal and / or a non-conductive polymer) and the first layer is a conductive material, such as stainless steel, titanium, tantalum, a conductive polymer, and / or the like. The core and the first layer can be a single (or the same) material, e.g., platinum. One skilled in the art will appreciate that additional configurations are possible.

[0052] In the illustrated embodiment, electronics unit 500 is removably attachable to sensor 200. Electronics unit 500 includes electronics circuitry associated with measuring and processing continuous analyte sensor data and is configured to execute algorithms associated with processing and calibrating sensor data. For example, electronics unit 500 can provide various aspects of the functionality of the sensor electronics module described in U.S. Patent Publication No. US-2009-0240120-A1 and U.S. Patent Application No. 13 / 247,856, filed September 28, 2011, entitled "ADVANCED CONTINUOUS ANALYTE MONITORING SYSTEM," the contents of which are incorporated herein by reference in their entireties. Electronics unit 500 can include hardware, firmware, and / or software that enables measurement of analyte levels via a glucose sensor, such as analyte sensor 200. For example, the electronics unit 500 may include a potentiostat, a power supply for providing power to the sensor 200, other components useful for signal processing and data storage, and preferably a telemetry module for one-way or two-way data communication between the electronics unit 500 and one or more receivers, repeaters, and / or display devices, such as devices 110-113. The electronics may be affixed to a printed circuit board (PCB) or the like and may take a variety of forms. For example, the electronics may take the form of integrated circuits (ICs), such as application specific integrated circuits (ASICs), microcontrollers, and / or processors. The electronics unit 500 may include sensor electronics configured to process the sensor information, e.g., store the data, analyze the data stream, calibrate the analyte sensor data, estimate analyte values, compare the estimated analyte values ​​to time-corresponding measured analyte values, and analyze various estimated analyte values.Examples of systems and methods for processing sensor analyte data are described herein and in U.S. Pat. No. 7,310,544, U.S. Pat. No. 6,931,327, U.S. Patent Publication No. 2005-0043598-A1, U.S. Patent Publication No. 2007-0032706-A1, U.S. Patent Publication No. 2007-0016381-A1, U.S. Patent Publication No. 2008-0033254-A1, U.S. Patent Publication No. 2005 ... Nos. 203360-A1, 2005-0154271-A1, 2005-0192557-A1, 2006-0222566-A1, 2007-0203966-A1, and 2007-0208245-A1, the contents of which are incorporated herein by reference in their entireties.

[0053] One or more repeaters, receivers, and / or display devices, such as key fob repeater 110, medical device receiver 111 (e.g., insulin delivery device and / or dedicated glucose sensor receiver), smartphone 112, portable computer 113, etc., are operably connected to the electronics unit, which is also referred to herein as a transmitter and / or sensor electronics body, to receive data from the electronics unit 500 and, in some embodiments, transmit data to the electronics unit 500. For example, sensor data may be transmitted from the sensor electronics unit 500 to one or more of the key fob repeater 110, medical device repeater 111, smartphone 112, portable computer 113, etc. In one embodiment, the display device includes an input module having a quartz crystal operably connected to an RF transceiver (not shown), which function together to transmit, receive, and synchronize the data stream from the electronics unit 500. However, the input module may be configured in any manner capable of receiving data from the electronics unit 500. Once received, the input module transmits the data stream to a processor that processes the data stream, as described in more detail below. The processor is a central control unit that performs processes such as storing data, analyzing the data stream, calibrating analyte sensor data, estimating analyte values, comparing estimated analyte values ​​with time-corresponding measured analyte values, analyzing variations in estimated analyte values, downloading data, and controlling the user interface by providing analyte values, prompts, messages, warnings, alarms, etc. The processor includes hardware to perform the processes described herein, such as read-only memory (ROM) providing permanent or semi-permanent storage of data, storage of data such as sensor ID (sensor identifier), receiver ID (receiver identifier), and programming for processing the data stream (e.g., programming for performing estimation and other algorithms described elsewhere herein), and random access memory (RAM) storing cache memory for the system and aiding in data processing.The output module, which may be integrated with and / or operatively connected to the processor, contains programming (and any processing that occurs within the processor) for generating output based on sensor data received from the electronics unit.

[0054] In some embodiments, the analyte value is displayed on a display device. In some embodiments, prompts or messages can be displayed on the display device to convey information to the user, such as reference outliers, requests for reference analyte values, treatment recommendations, deviations of measured analyte values ​​from estimated analyte values, etc. Additionally, prompts may be displayed to guide the user through calibration or troubleshooting of the calibration.

[0055] Additionally, the data output from the output module can provide wired or wireless one-way or two-way communication between the receiver and an external device. The external device can be any device that interfaces or communicates with the receiver. In some embodiments, the external device is a computer and the receiver can download current or past data for retrospective analysis, for example, by a physician. In some embodiments, the external device is a modem and the receiver can send alerts, warnings, emergency messages, etc., over a communication line to a physician or other party, such as a family member. In some embodiments, the external device is an insulin pen and the receiver can communicate treatment recommendations, such as insulin amount and time, to the insulin pen. In some embodiments, the external device is an insulin pump and the receiver can communicate treatment recommendations, such as insulin amount and time, to the insulin pump. The external device can include other technology or medical devices, such as, for example, a pacemaker, an implantable analyte sensor patch, other infusion devices, telemetry devices, etc. The receiver may communicate with the external device and / or any number of additional devices via any suitable communications protocol, including radio frequency, Bluetooth, Universal Serial Bus (USB), Wireless Local Area Network (WLAN) communications standards (including IEEE 802.11, 802.15, 802.20, 802.22, and other 802 communications protocols), ZigBee, wireless (e.g., cellular) telecommunications, paging network communications, magnetic induction, satellite data communications, GPRS, ANT, and / or proprietary communications protocols.

[0056] The implementations described herein generally discuss sensors configured with one or more sensor wires. However, it will be understood that the sensors are not limited to such wire shapes or linear arrangements. Rather, the sensors may be implemented as planar sensors, volume sensors, point sensors, or in other shapes that will be understood in light of this description. Membrane system

[0057] The membrane system disclosed herein is suitable for use with implantable devices in contact with biological fluids. For example, the membrane system may be utilized with implantable devices such as devices for monitoring and determining analyte levels in biological fluids, such as devices for monitoring glucose levels in individuals with diabetes. In some embodiments, the analyte measuring device is a continuous device. The analyte measuring device provides a raw signal using any suitable sensing element, including but not limited to those involving enzymatic, chemical, physical, electrochemical, spectrophotometric, polarimetric, calorimetric, radiometric, immunochemical, or similar elements.

[0058] Although some of the following description, including the membrane systems described and their methods of use, are directed to glucose measurement devices, these membrane systems are not limited to use in devices that measure or monitor glucose. These membrane systems are suitable for use in any of a variety of devices, including, for example, devices that detect and quantify other analytes present in biological fluids (e.g., cholesterol, amino acids, alcohol, galactose, and lactate), cell transplantation devices (see, for example, U.S. Patent Nos. 6,015,572, 5,964,745, and 6,083,523), drug delivery devices (see, for example, U.S. Patent Nos. 5,458,631, 5,820,589, and 5,972,369), and the like.

[0059] In one embodiment, the analyte measuring device is an implantable glucose sensor, such as those described with reference to U.S. Patent No. 6,001,067 and U.S. Patent Publication No. US-2005-0027463-A1, which are incorporated herein by reference in their entireties. In another embodiment, the analyte measuring device is a glucose sensor, such as those described with reference to U.S. Patent Publication No. US-2006-0020187-A1, which are incorporated herein by reference in their entireties. In yet other embodiments, the sensor is configured to be implanted in a host's blood vessel or outside the body, for example, as described in U.S. Patent Publication Nos. US-2007-0027385-A1, US Patent Publication Nos. US-2008-0119703-A1, US Patent Publication Nos. US-2008-0108942-A1, and US Patent Publication Nos. US-2007-0197890-A1, which are incorporated herein by reference in their entireties. In some embodiments, the sensor is configured as a dual electrode sensor, for example, as described in U.S. Patent Publication Nos. US-2005-0143635-A1, US-2007-0027385-A1, US-2007-0213611-A1, and US-2008-0083617-A1, which are incorporated by reference in their entireties. In an alternative embodiment, the continuous glucose sensor includes a sensor, such as, for example, a sensor described in U.S. Patent No. 6,565,509 to Say et al. In another alternative embodiment, the continuous glucose sensor includes a subcutaneous sensor, such as, for example, a sensor described with reference to U.S. Patent No. 6,579,690 to Bonnecaze et al. or U.S. Patent No. 6,484,046 to Say et al. In another alternative embodiment, the continuous glucose sensor includes a refillable subcutaneous sensor, such as, for example, a sensor described with reference to U.S. Patent No. 6,512,939 to Colvin et al. In yet another alternative embodiment, the continuous glucose sensor includes an intravascular sensor, such as the sensor described with reference to U.S. Patent No. 6,477,395 to Schulman et al. In another alternative embodiment, the continuous glucose sensor includes an intravascular sensor, such as the sensor described with reference to U.S. Patent No. 6,424,847 to Mastrototaro et al.In some embodiments, the electrode system is configured as described in U.S. Pat. No. 7,157,528 to Ward, U.S. Pat. No. 6,212,416 to Ward et al., U.S. Pat. No. 6,119,028 to Schulman et al., U.S. Pat. No. 6,400,974 to Lesho, U.S. Pat. No. 6,595,919 to Berner et al., U.S. Pat. No. 6,141,573 to Kurnik et al., U.S. Pat. No. 6,122,536 to Sun et al., European Patent Publication No. 1153571 to Varall et al., U.S. Pat. No. 6,512,939 to Colvin et al., U.S. Pat. No. 5,512,939 to Slate ... No. 6,514,718 to Heller et al., U.S. Patent No. 5,985,129 to Gough et al., PCT International Publication No. WO 4 / 021877 to Caduff, U.S. Patent No. 5,494,562 to Maley et al., U.S. Patent No. 6,120,676 to Heller et al., and U.S. Patent No. 6,542,765 to Guy et al. In general, it will be understood that the disclosed embodiments are applicable to a variety of continuous analyte measurement device configurations.

[0060] In some embodiments, long-term sensors (e.g., fully implantable or intravascular) are configured and positioned to function for a period of about 30 days or less to about a year or more (e.g., a sensor session). In some embodiments, short-term sensors (e.g., transcutaneous or intravascular) are configured and positioned to function for a period of about several hours to about 30 days, including about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, or 29 days (e.g., a sensor session). As used herein, the term "sensor session" is a broad term and refers to, but is not limited to, the period during which a sensor is applied (e.g., implanted) to a host or used to obtain a sensor value. For example, in some embodiments, a sensor session extends from the time of sensor implantation (e.g., including insertion of the sensor into subcutaneous tissue and placing the sensor in fluid communication with the host's circulatory system) to the time the sensor is removed.

[0061] Generally, the membrane system includes multiple domains, such as an electrode domain, an interference domain, an enzyme domain, a diffusion resistance domain, and a biointerface domain. The membrane system can be deposited on the exposed electroactive surface using known thin film techniques (e.g., vapor deposition, spraying, electrodeposition, dipping, brush coating, film coating, drop coating, etc.). Following membrane material deposition, additional steps, such as drying, baking, and curing (e.g., UV curing, heat curing, moisture curing, radiation curing, etc.), can be applied to enhance certain properties, such as mechanical properties, signal stability, and selectivity. In a typical process, upon deposition of the interference layer membrane, the enzyme layer has a "dry film" thickness of about 0.05 μm to about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16 μm. The "dry film" thickness refers to the thickness of the cured film cast from the coating formulation by standard coating techniques.

[0062] FIG. 2A is a cross-sectional view through the sensor illustrating one embodiment of the membrane system 32. In this particular embodiment, the membrane system includes an electrode layer 42, an enzyme layer 44, a diffusion resistance layer 46, and a biointerface layer 48, all of which are located around the working electrode of the sensor 38, all of which are described in more detail elsewhere herein. In some embodiments, an integrated diffusion resistance domain and a biointerface layer may be included in the membrane system (e.g., the functionality of both layers is incorporated into one domain). In some embodiments, the sensor is configured for short-term implantation (e.g., about 1-30 days). However, the membrane system 32 may be modified for use in other devices, for example, by including only one or more of the domains, or additional domains.

[0063] 2B is a cross-sectional view through one embodiment of the sensor illustrating another embodiment of membrane system 32. In this particular embodiment, the membrane system includes an interference-reducing or blocking layer 43, an enzyme layer 44, a diffusion resistance layer 46, and a biointerface layer 48 positioned around the working electrode of sensor 38, all of which are described in more detail elsewhere herein.

[0064] 2C is a cross-sectional view through one embodiment of the sensor illustrating yet another embodiment of membrane system 32. In this particular embodiment, the membrane system includes an interference reduction or blocking layer 43, an enzyme layer 44, and an integrated diffusion resistance / biointerface layer 47 positioned around the working electrode of the sensor, all of which are described in more detail elsewhere herein.

[0065] In some embodiments, the membrane system may include a biointerface layer 48 that includes a surface-modified biointerface polymer, as described in more detail elsewhere herein. However, the sensing membrane 32 of some embodiments may also include multiple domains or layers, such as an electrode domain (e.g., as illustrated in FIG. 2A), an interference reduction or blocking domain (e.g., as illustrated in FIGS. 2B and 2C), or a cell disruption domain (not shown), such as those described in more detail elsewhere herein and in U.S. Patent Publication No. US-2006-0036145-A1, which is incorporated herein by reference in its entirety.

[0066] For example, it is understood that sensing membranes modified for other sensors may include fewer or additional layers. For example, in some embodiments, the membrane system may include one electrode layer, one enzyme layer, and two biointerface layers, while in other embodiments, the membrane system may include one electrode layer, two enzyme layers, and one biointerface layer. In some embodiments, the biointerface layer is configured to function as a diffusion resistance domain and can control the flux of analyte (e.g., glucose) to the underlying membrane layer.

[0067] In some embodiments, one or more domains of the sensing membrane may be formed from materials such as silicone, polytetrafluoroethylene, polyethylene-co-tetrafluoroethylene, polyolefins, polyesters, polycarbonates, biostable polytetrafluoroethylene, homopolymers, copolymers, terpolymers of polyurethane, polypropylene (PP), polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polybutylene terephthalate (PBT), polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), polyurethane, polyurethane urea, cellulose polymers, poly(ethylene oxide), poly(propylene oxide) and copolymers and blends thereof, polysulfone and its block copolymers (including, for example, diblock, triblock, alternating, random, and graft copolymers).

[0068] In some embodiments, the sensing membrane may be deposited on the electroactive surface of the electrode material using known thin or thick film techniques (e.g., spraying, electrodeposition, dipping, etc.) It should be understood that the sensing membrane located on the working electrode need not have the same structure as the sensing membrane located on the reference electrode, e.g., an enzyme domain deposited on the working electrode does not necessarily have to be deposited on the reference or counter electrodes.

[0069] Although the exemplary embodiment illustrated in Figures 2A-2C involves a circumferentially extending membrane system, the membranes described herein may be applied to any planar or non-planar surface.

[0070] 3A-3C illustrate an embodiment of an in vivo portion of a continuous analyte sensor 400 that includes an elongated conductor 402. The elongated conductor 402 includes a core 410 (see FIG. 3B) and a first layer 412 that at least partially surrounds the core. The first layer includes a working electrode (e.g., located in a window 406) and a membrane 408 that is located on the working electrode. In some embodiments, the core and the first layer can be a single material (e.g., platinum, etc.). In some embodiments, the elongated conductor is a composite of at least two materials, such as a composite of two conductive materials, or a composite of at least one conductive material and at least one non-conductive material. In some embodiments, the elongated conductor includes multiple layers. In certain embodiments, there are at least two concentric or annular layers, such as a core formed of a first material and a first layer formed of a second material. However, in some embodiments, additional layers may be included. In some embodiments, the layers are coaxial.

[0071] The elongated conductors may be long and thin, yet flexible and strong. For example, in some embodiments, the smallest dimension of the elongated conductor is less than about 0.1 inches, 0.075 inches, 0.05 inches, 0.025 inches, 0.01 inches, 0.004 inches, or 0.002 inches. Although the elongated conductors are illustrated in FIGS. 3A-3C as having a circular cross section, in other embodiments, the cross section of the elongated conductor may be oval, rectangular, triangular, polygonal, star-shaped, C-shaped, T-shaped, X-shaped, Y-shaped, irregular, etc. In one embodiment, a conductive wire electrode is used as the core. To such a clad electrode, two additional conductive layers may be added (e.g., with an intervening insulating layer that provides for electrical isolation). The conductive layers may be composed of any suitable material. In certain embodiments, it may be desirable to use a conductive layer that includes conductive particles (i.e., particles of a conductive material) in a polymer or other binder.

[0072] The materials used to form the elongated conductors (e.g., stainless steel, titanium, tantalum, platinum, platinum-iridium, iridium, certain polymers, and / or the like) can be strong and rigid, thus preventing breakage. In some embodiments, the small diameter of the sensor provides flexibility to these materials, and thus to the sensor as a whole. Thus, the sensor can withstand repeated forces exerted on it by the surrounding tissue.

[0073] In addition to providing structural support, resilience, and flexibility, in some embodiments, the core 410 or components thereof provide electrical conduction for an electrical signal from the working electrode to the sensor electronics (not shown). In some embodiments, the core 410 comprises a conductive material, such as stainless steel, titanium, tantalum, conductive polymers, and / or the like. However, in other embodiments, the core is formed from a non-conductive material, such as a non-conductive polymer. In still other embodiments, the core comprises multiple layers of material. For example, in one embodiment, the core comprises an inner core and an outer core. In further embodiments, the inner core is formed from a first conductive material and the outer core is formed from a second conductive material. For example, in some embodiments, the first conductive material is stainless steel, titanium, tantalum, conductive polymers, alloys, and / or the like, and the second conductive material is a conductive material selected to provide electrical conduction between the core and the first layer and / or to adhere the first layer to the core (i.e., where the first layer is formed from a material that does not adhere well to the core material). In another embodiment, the core is formed of a non-conductive material (e.g., a non-conductive metal and / or a non-conductive polymer, etc.) and the first layer is formed of a conductive material, such as stainless steel, titanium, tantalum, a conductive polymer, and / or the like. The core and the first layer can be a single (or the same) material, e.g., platinum. One skilled in the art will appreciate that additional configurations are possible.

[0074] 3A-3C, the first layer 412 may be formed of an electrically conductive material, and the working electrode may be an exposed portion of a surface of the first layer 412. Thus, the first layer 412 may be formed of a material configured to provide a suitable electroactive surface for a working electrode, such as, but not limited to, platinum, platinum-iridium, gold, palladium, iridium, graphite, carbon, a conductive polymer, an alloy, and / or the like.

[0075] As illustrated in Figures 3B and 3C, the second layer 404 surrounds at least a portion of the first layer 412, thereby defining the boundary of the working electrode. In some embodiments, the second layer 404 functions as an insulator and is formed of an insulating material, such as polyimide, polyurethane, parylene, or any other known insulating material. For example, in one embodiment, the second layer is disposed on the first layer and configured such that the working electrode is exposed through the window 406. In some embodiments, an elongated conductor is provided that includes a core, a first layer, and a second layer. A portion of the second layer can be removed to form the window 406, thereby exposing the electroactive surface of the working electrode (i.e., the exposed surface of the first layer 412). In some embodiments, a portion of the second layer and (optionally) the third layer can be removed to form the window 406, thus exposing the working electrode. Removal of coating material from one or more layers of the elongated conductor (eg, to expose the electroactive surface of the working electrode) can be accomplished by hand, excimer laser treatment, chemical etching, laser ablation, grit blasting, and the like.

[0076] The sensor may further include a third layer 414 that includes a conductive material. For example, the third layer 414 may include a reference electrode that may be formed of a silver-containing material and is applied over the second layer 404 (i.e., the insulator).

[0077] The elongated conductor 402 may further include one or more intermediate layers (not shown) located between the core 410 and the first layer 412. For example, the intermediate layer may be one or more of an insulator, a conductor, a polymer, and / or an adhesive.

[0078] It is contemplated that the ratio of the thickness of the silver / silver chloride layer to the thickness of the insulator (e.g., polyurethane or polyimide, etc.) layer may be controlled to allow for certain errors (i.e., errors associated with the etching process) due to defects resulting from the etching process cutting deeper than intended, thereby unintentionally exposing the electroactive surface. This ratio may vary depending on the type of etching process used, whether it is laser ablation, grit blasting, chemical etching, or some other etching method. In one embodiment where laser ablation is performed to remove the silver / silver chloride layer and the polyurethane layer, the ratio of the thickness of the silver / silver chloride layer to the thickness of the polyurethane layer may be about 1:5 to about 1:1, or about 1:3 to about 1:2.

[0079] In some embodiments, the core 410 comprises a non-conductive polymer and the first layer 412 comprises a conductive material. Such a sensor configuration advantageously provides reduced material costs in that typically expensive materials are replaced with less expensive materials. For example, the core 410 may be formed of a non-conductive polymer, such as a nylon or polyester filament, string, or cord, which may be coated and / or plated with a conductive material, such as platinum, platinum-iridium, gold, palladium, iridium, graphite, carbon, conductive polymers, and alloys, or combinations thereof.

[0080] As illustrated in Figures 3C and 3D, the sensor may also include a membrane 408, such as those discussed elsewhere herein, for example with reference to Figures 2A-2C. The membrane 408 may include an enzyme layer (not shown), as described elsewhere herein. For example, the enzyme layer may include a catalyst or enzyme configured to react with the analyte. For example, the enzyme layer may be an immobilized enzyme layer including glucose oxidase. In other embodiments, the enzyme layer may be impregnated with other oxidases, including, for example, galactose oxidase, cholesterol oxidase, amino acid oxidase, alcohol oxidase, lactate oxidase, or uricase.

[0081] FIG. 3B is a schematic diagram illustrating an embodiment of an elongated conductor 402 or elongated body, the elongated conductor being formed from at least two layers of materials and / or conductive materials, as described in more detail elsewhere herein. The term "electrode" may be used herein to refer to an elongated conductor that includes an electroactive surface that detects an analyte. In some embodiments, the elongated conductor provides an electrical connection between the electroactive surface (i.e., working electrode) and the sensor electronics (not shown). In certain embodiments, each electrode (i.e., the elongated conductor on which the electroactive surface is located) is formed from a thin wire having a diameter of about 0.001 inches or less to about 0.01 inches or more. Each electrode may be formed, for example, from plated insulators, plated wire, or bulk conductive material. For example, in some embodiments, the wire and / or elongated conductor used to form the working electrode is about 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, or 0.045 inches in diameter.

[0082] Additionally, the first layer may include an electroactive surface (i.e., the portion exposed through window 406). The exposed electroactive surface may be a working electrode. For example, if the sensor is an enzymatic electrochemical analyte sensor, the analyte reacts enzymatically with an enzyme within a membrane covering at least a portion of the electroactive surface. This reaction produces electrons (e - For example, in the detection of glucose, where glucose oxidase produces hydrogen peroxide as a by-product, hydrogen peroxide can be converted to two protons (2H + ), 2 electrons (2e - ), and reacts with the surface of the working electrode producing one oxygen molecule (O2), which produces a current that is detected.

[0083] As previously described with reference to FIG. 3A and illustrated in FIG. 3C, the insulator 404 is disposed on at least a portion of the elongated conductor 402. In some embodiments, the sensor is configured and arranged such that the elongated body includes a core 410 and a first layer 412, with a portion of the first layer 412 exposed through a window 406 in the insulator 404. In other embodiments, the sensor is configured and arranged such that the elongated body 402 includes a core 410 embedded in the insulator 404, with a portion of the core 410 exposed through a window 406 in the insulator 404. For example, the insulating material may be applied (e.g., by screen printing, inkjet printing, and / or block printing) to the elongated body 402 in a configuration designed to leave at least a portion of the surface of the first layer 412 (or a surface of the core 410) exposed. For example, the insulating material may be printed in a pattern that does not cover a portion of the elongated body 402. Alternatively, a portion of the elongated body 402 may be masked prior to application of the insulating material. Removal of the mask after application of the insulating material may expose a portion of elongate body 402 .

[0084] In some embodiments, the insulating material 404 comprises a polymer, such as a non-conductive (i.e., dielectric) polymer. Dip coating, spray coating, vapor deposition, printing, and / or other thin and / or thick film coating or deposition techniques can be used to deposit the insulating material on the elongated body 402 and / or the core 410. For example, in some embodiments, the insulating material is applied as a layer less than about 5 μm, or from about 5, about 10, or about 15 μm to about 20, about 25, about 30, or about 35 μm or more thick. The insulator may be applied as a single layer of material, or as two or more layers composed of the same or different materials, as described elsewhere herein. Alternatively, the conductive core does not require a coating of the insulator. In some embodiments, the insulating material defines the electroactive surface of the analyte sensor (i.e., the working electrode). For example, the surface of the conductive core (e.g., a portion of the first layer 412, etc.) may remain exposed during the application of the insulator, or a portion of the applied insulator may be removed to expose a portion of the surface of the conductive core, as described above.

[0085] In some embodiments where the sensor has an insulator disposed on an insulated elongated body or conductive structure, a portion of the insulating material may be peeled off or otherwise removed, for example, by hand, excimer laser treatment, chemical etching, laser ablation, grit blasting (e.g., with sodium bicarbonate or other suitable grit), etc., to expose the electroactive surface(s). In one exemplary embodiment, grit blasting is implemented to expose the electroactive surface(s) by utilizing a grit material that is hard enough to, for example, cut through polymeric materials, but soft enough to minimize or avoid damage to the underlying metal electrodes (e.g., platinum electrodes). A variety of "grit" materials (e.g., sand, talc, walnut shells, crushed plastic, sea salt, etc.) can be used, and in some embodiments, sodium bicarbonate is an advantageous grit material because it is hard enough to, for example, cut through parylene coatings without damaging the underlying platinum conductors. Additional benefits of sodium bicarbonate blasting include its abrasive action on metal as it peels off the polymer layer, thereby eliminating a cleaning step that may otherwise be necessary. Alternatively, portions of the electrodes or other conductors may be masked prior to depositing the insulator to maintain exposed electroactive surface area.

[0086] The electroactive surface of the working electrode may be exposed by the formation of a window 406 in the insulator 404. The electroactive window 406 of the working electrode may be configured to measure the concentration of an analyte.

[0087] In some embodiments, a silver wire is formed on and / or fabricated within the sensor and then chlorinated to form a silver / silver chloride reference electrode. Advantageously, the chlorination of the silver wire as described herein allows for the fabrication of a reference electrode with good in vivo performance. By controlling the quantity and amount of silver chlorination to form silver / silver chloride, improved intermittency, stability, and extended life of the reference electrode can be obtained in some embodiments. Furthermore, the use of silver chloride as described above allows for a relatively inexpensive and simple fabrication of the reference electrode.

[0088] 3B and 3C, the reference electrode 414 may include a silver-containing material (e.g., silver / silver chloride) applied over at least a portion of the insulating material 404, as discussed in more detail elsewhere herein. For example, the silver-containing material may be applied using thin and / or thick film techniques, such as, but not limited to, dipping, spraying, printing, electrodeposition, vapor deposition, spin coating, and sputter deposition, as described elsewhere herein. For example, a silver or silver chloride-containing paint (or similar formulation) may be applied to a reel of insulated conductive core. Alternatively, a reel of insulated elongated body (or core) may be cut into single unit pieces (i.e., "singularized") and a silver-containing ink may be pad printed thereon. In yet other embodiments, the silver-containing material is applied as a silver foil. For example, an adhesive may be applied to the insulated elongated body, and then a silver foil may be wrapped around it. Alternatively, the sensor is wrapped with Ag / AgCl particles whereby a sufficient amount of silver is affixed to and / or embedded in and / or otherwise adhered to the adhesive such that the particles function as a reference electrode. In some embodiments, the reference electrode of the sensor comprises a sufficient amount of silver chloride for the sensor to measure and / or detect an analyte for at least 3 days.

[0089] In certain embodiments, the biointerface layer is formed of a biointerface polymer. The biointerface polymer is polyzwitterionic. The biointerface polymer may also include polyurethane and / or polyurea segments. For example, the biointerface polymer may include polyurethane copolymers, such as polyether-urethane-urea, polycarbonate-urethane, polyether-urethane, silicone-polyether-urethane, silicone-polycarbonate-urethane, polyester-urethane, polyurethane-urea, and the like. These polyurethane and / or polyurea segments are referred to herein as "hard segments" because they include urea and / or urethane linkages formed from polyisocyanates and short chain polyols or polyamines, moieties that are rich in hydrogen bonds. These segments may also be relatively hydrophobic. In addition to the polyurethane and / or polyurea hard segments, the disclosed biointerface polymers may also include soft segments that have relatively poor hydrogen bonding. The soft segments are typically composed of polyols, such as polycarbonates, polyesters, polyethers, polyarylenes, and polyalkylenes. The soft segments can be either hydrophobic or hydrophilic. In certain embodiments, the biointerface layer is formed of a biointerface polymer, which includes polyurethane and / or polyurea segments and one or more zwitterionic repeat units. In some embodiments, the biointerface polymer is formed of a polyurethaneurea having betaine groups and non-ionic hydrophilic polyethylene oxide segments incorporated into the polymer.

[0090] In certain embodiments, the enzyme layer is formed of an enzyme layer polymer and an active enzyme, the enzyme layer polymer comprising polyurethane and / or polyurea segments and one or more zwitterionic repeat units. In some embodiments, the enzyme layer coating is formed of a polyurethaneurea having carboxyl betaine groups and non-ionic hydrophilic polyethylene oxide segments incorporated into the polymer, the polyurethaneurea polymer is dissolved in an organic or non-organic solvent system according to the given coating formulation, crosslinked with an isocyanate crosslinker, and cured at a moderate temperature of about 50°C. The solvent system can be a single solvent or a mixture of solvents to aid in the dissolution or dispersion of the polymer. The solvent can be the one selected as the polymerization medium or one that is added after the polymerization is completed. The solvent is preferably selected from those that have a lower boiling point to facilitate drying, a low ability to denature the enzyme, and low toxicity for implantation applications. Examples of these solvents include water, aliphatic ketones, esters, ethers, alcohols, carbohydrates, and the like. Depending on the final thickness of the enzyme layer and the solution viscosity (related to the percent of polymer solids), the coating may be applied in a single step or multiple repeated steps of a selected process such as dipping to build up the desired thickness. In yet other embodiments, the enzyme layer polymer is formed of a polyurethaneurea having carboxylic acid and carboxylbetaine groups incorporated into the polymer and non-ionic hydrophilic polyethylene oxide segments, the polyurethaneurea polymer is dissolved in an organic or non-organic solvent system in the coating formulation and crosslinked with a carbodiimide (e.g., 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and cured at moderate temperatures of about 50° C. Other crosslinkers such as polyfunctional aziridines may also be used.

[0091] In another embodiment, the enzyme layer is formed of a polyurethaneurea with sulfobetaine groups and non-ionic hydrophilic polyethylene oxide segments incorporated into the polymer, the polyurethaneurea polymer being dissolved in an organic or non-organic solvent system according to a given coating formulation, solubilized with an isocyanate crosslinker, and cured at a moderate temperature of about 50°C. The solvent system can be a single solvent or a mixture of solvents to aid in the dissolution or dispersion of the polymer. The solvent can be the one selected as the polymerization medium or one added after the polymerization is completed. The solvent is preferably selected from those with lower boiling points to facilitate drying and low toxicity for embedded applications. Examples of these solvents include lipid soluble ketones, esters, ethers, alcohols, carbohydrates, etc. Depending on the final thickness of the enzyme layer and the solution viscosity (related to the percentage of polymer solids), the coating can be applied in a single step or multiple repeated steps of a selected process such as dipping to build up the desired thickness. In yet other embodiments, the enzyme layer polymer is formed of a polyurethaneurea having unsaturated hydrocarbon and sulfobetaine groups incorporated into the polymer and non-ionic hydrophilic polyethylene oxide segments, the polyurethaneurea polymer is dissolved in an organic or non-organic solvent system in the coating formulation, crosslinked with heat or radiation, including UV, LED light, e-beam, etc., in the presence of an initiator, and cured at moderate temperatures of about 50° C. Examples of unsaturated hydrocarbons include allyl groups, vinyl groups, acrylates, methacrylates, alkenes, alkynes, etc. Sensor Electronics

[0092] In general, an analyte sensor system has associated therewith electronics, also referred to as a "computer system," which may include hardware, firmware, or software that allows for the measurement and processing of data associated with analyte levels in a host. In one exemplary embodiment of an electrochemical sensor, the electronics includes a potentiostat, a power supply for providing power to the sensor, and other components useful for signal processing. In additional embodiments, some or all of the electronics may communicate with the sensor or other parts of the electronics in a wired or wireless manner. For example, a potentiostat disposed on the device may be hardwired to the rest of the electronics (e.g., processor, recorder, transmitter, receiver, etc.) at the bedside. In another example, one piece of electronics is wirelessly connected to another piece of electronics (e.g., receiver), for example, by infrared (IR) or radio frequency (RF). It is contemplated that other embodiments of the electronics may be useful for providing sensor data outputs such as those described in U.S. Patent Publication No. US-2005-0192557-A1, U.S. Patent Publication No. US-2005-0245795-A1, U.S. Patent Publication No. US-2005-0245795-A1, U.S. Patent Publication No. US-2005-0245795-A1, U.S. Patent Publication No. US-2008-0119703-A1, and U.S. Patent Publication No. US-2008-0108942-A1, each of which is incorporated herein by reference in its entirety.

[0093] In a preferred embodiment, the potentiostat is operably connected to the electrode(s) (e.g., as described elsewhere herein) and deflects the sensor to allow measurement of a current signal indicative of the analyte concentration (also referred to as the analog portion) in the host. In some embodiments, the potentiostat includes a resistor that converts the current to a voltage. In some alternative embodiments, a current-to-frequency converter is provided that is configured to continuously integrate the measured current, for example, using a charge counting device. In some embodiments, the electronics includes an A / D converter that digitizes the analog signal into a digital signal, also referred to as "counts," for processing. Thus, the resulting raw data stream in counts (also referred to as raw sensor data) is directly related to the current measured by the potentiostat.

[0094] Generally, the electronics includes a processor module, which includes a central control unit that controls the processing of the sensor system. In some embodiments, the processor module includes a microprocessor, although computer systems other than a microprocessor can be used to process the data described herein, for example, an ASIC can be used for some or all of the sensor's central processing. The processor typically provides semi-permanent storage of data, such as storage of data such as a sensor identifier (ID), and programming for processing the data stream (e.g., programming for data smoothing or signal artifact replacement, such as programming described in U.S. Patent Publication No. US-2005-0043598-A1). Additionally, the processor may be used to temporarily store cache memory for the system, such as recent sensor data. In some embodiments, the processor module includes memory storage components, such as ROM, RAM, dynamic RAM, static RAM, non-static RAM, EEPROM, overwritable ROM, flash memory, etc.

[0095] In some embodiments, the processor module includes a digital filter, such as an infinite impulse response (IIR) or finite impulse response (FIR) filter, configured to smooth the raw data stream. Generally, the digital filter is programmed to filter data sampled at predefined time intervals (also referred to as the sampling rate). In some embodiments where the potentiostat is configured to measure the analyte at discrete time intervals, these time intervals determine the sampling rate of the digital filter. In some alternative embodiments where the potentiostat is configured to measure the analyte continuously, for example using a current-to-frequency converter as described above, the processor module may be programmed to request digital values ​​from the A / D converter at predefined time intervals, also referred to as collection times. In these alternative embodiments, the values ​​obtained by the processor are advantageously averaged over the collection time due to the continuity of the current measurements. Thus, the collection time determines the sampling rate of the digital filter.

[0096] In some embodiments, the processor module is configured to construct a data packet for transmission to an external source, e.g., RF transmission to a receiver. Generally, the data packet includes a number of bits that may include a preamble unique identifier (e.g., a sensor ID code) that identifies the electronics unit, the receiver, or both, data (e.g., raw data, filtered data, or an integrated value), or error detection or correction. Preferably, the data (transmit) packet has a length of about 8 bits to about 128 bits, preferably about 48 bits, although in certain embodiments, larger or smaller packets may be desirable. The processor module may be configured to transmit any combination of raw data or filtered data. In one exemplary embodiment, the transmit packet includes a fixed preamble unique ID of the electronics unit, a single 5-minute average (e.g., integrated) sensor data value, and a cyclic redundancy code (CRC).

[0097] In some embodiments, the processor further performs processes such as storing data, analyzing the data stream, calibrating the analyte sensor data, estimating analyte values, comparing the estimated analyte values ​​with time-corresponding measured analytes, analyzing variations in the estimated analyte values, downloading data, and controlling a user interface by providing analyte values, prompts, messages, warnings, alarms, etc. In such cases, the processor includes hardware to perform the processes described herein, e.g., flash memory provides permanent or semi-permanent storage of data, storage of data such as sensor ID, receiver ID, etc., as well as programming for processing the data stream (e.g., programming for performing estimation and other algorithms described elsewhere herein), and random access memory (RAM) stores cache memory for the system and aids in data processing. Alternatively, certain portions of the data processing (e.g., described with reference to the processor elsewhere herein) can be accomplished in a separate (e.g., remote) processor and may be configured for wired or wireless connection thereto.

[0098] In some embodiments, an output module integrated with or operatively connected to the processor includes programming for generating an output based on the data stream received from the sensor system, and the processing thereof occurring within the processor, hi some embodiments, the output is generated via a user interface. Interfering substances

[0099] Interferents are molecules or other species that can cause a sensor to generate false positive or false negative analyte signals (e.g., non-analyte related signals). Some interferents are reduced or oxidized at the electrochemically reactive surface of the sensor, while others interfere with the ability of the enzyme used (e.g., glucose oxidase) to react with the analyte being measured. Still other interferents react with the enzyme (e.g., glucose oxidase) to produce by-products that are electrochemically active. Interferents may exaggerate or mask the response signal, leading to false or misleading results. For example, a false positive signal may make the host's analyte concentration (e.g., glucose concentration) appear higher than the true analyte concentration. False positive signals can pose clinically significant problems in some conventional sensors. For example, in a severe hypoglycemic situation where the host has ingested an interferent (e.g., acetaminophen), the resulting artificially high glucose signal may lead the host to believe that they are euglycemic or hyperglycemic. In response, the host may make an inappropriate therapeutic decision by injecting too much insulin or by doing nothing when the appropriate course of action would be to start a meal. In turn, this inappropriate action or inaction may lead to a hypoglycemic episode that is dangerous to the host. Thus, certain embodiments contemplated herein include membrane systems that substantially reduce or eliminate the effect of interferents on analyte measurements. These membrane systems include one or more domains that can block or substantially reduce the flow of interferents to the electroactive surface of the electrode, and can reduce noise and improve the accuracy of the sensor, as described in more detail in U.S. Patent Publication No. US-2009-0247856-A1. Drift

[0100] As used herein, the term "drift" is a broad term and its ordinary and customary meaning is given to those skilled in the art (and is not limited to any special or customized meaning), and refers to, but is not limited to, a change in the sensitivity of a sensor over time. Drift can be driven by changes in the permeability of the sensor membrane system, which can be particularly evident in embodiments using polyurethane diffusion-resistant domains. Without being bound by theory, it is believed that permeability changes in such systems result from rearrangements of the diffusion-resistant domain polyurethane polymer chains that bring more hydrophilic components to the surface, or that otherwise allow better access to the hydrophilic polymer components during hydration of the membrane system. Thus, increasing the hydration rate or increasing the wettability of the membrane system reduces system drift.

[0101] Due to electrostatically induced hydration, polymers and crosslinked coatings of zwitterionic compounds have near instantaneous wettability. As discussed in more detail below, including a base polymer with a minimum glass transition temperature, measured using ASTM D3418, of greater than -50°C and a maximum tensile strength, measured by ASTM D1708, of greater than 6000 psi can result in reduced sensor drift. Drift can be characterized as less than 10% signal change at 2 hours after initiation. membrane manufacturing

[0102] The polymers of the preferred embodiments can be processed by solution-based techniques such as spraying, dipping, casting, electrospinning, deposition, spin-coating, coating, etc. Water-based polymer emulsions can be made to form films by methods similar to those used for solvent-based materials. In both cases, evaporation of the volatile liquid (e.g., organic solvent or water) leaves a film of the polymer. Crosslinking of the deposited film or layer can be done by many methods using multifunctional reactive components. Liquid systems can be cured by heat, moisture, high energy radiation, ultraviolet light, or by completing a reaction that produces the final polymer in the mold or on the substrate to be coated.

[0103] In some embodiments, the wettability of the membrane (and by extension the degree of sensor drift exhibited by the sensor) can be tuned and / or controlled by creating covalent crosslinks between surface active group-containing polymers, functional group-containing polymers, polymers with zwitterionic groups (or precursors or derivatives thereof), and combinations thereof. Crosslinking can have a substantial effect on the film structure, which in turn can affect the wettability of the film surface. Crosslinking can also affect film tensile strength, mechanical strength, water absorption rate, and other properties.

[0104] The crosslinked polymers may have different crosslink densities. In certain embodiments, crosslinking is used to promote crosslinking between layers. In other embodiments, heat is used to form crosslinks instead of (or in addition to) the crosslinking techniques described above. For example, in some embodiments, imide and amide bonds may form between two polymers as a result of high temperature. In some embodiments, photocrosslinking can be performed to form covalent bonds between the polycationic layer(s) and the polyanionic layer(s). One major advantage to photocrosslinking is that it offers the possibility of patterning. In certain embodiments, patterning using photocrosslinking is performed to modify the film structure and thus tune the wettability of the membrane.

[0105] Polymers with domains or segments functionalized to allow crosslinking can be made by methods known in the art. For example, polyurethaneurea polymers with aromatic or aliphatic segments with electrophilic functional groups (e.g., carbonyl, aldehyde, anhydride, ester, amide, isocyano, epoxy, allyl, or halo groups) can be crosslinked with crosslinkers with multiple nucleophilic groups (e.g., hydroxyl, amine, urea, urethane, or thio groups). In further embodiments, polyurethaneurea polymers with aromatic or aliphatic segments with nucleophilic functional groups can be crosslinked with crosslinkers with multiple electrophilic groups. Still further, polyurethaneurea polymers with hydrophilic segments with nucleophilic or electrophilic functional groups can be crosslinked with crosslinkers with multiple electrophilic or nucleophilic groups. Unsaturated functional groups on the polyurethaneurea can also be used for crosslinking by reacting with multivalent free radical agents. Non-limiting examples of suitable crosslinkers include isocyanates, carbodiimides, glutaraldehyde, aziridines, silanes or other aldehydes, epoxies, acrylates, free radical agents, ethylene glycol diglycidyl ether (EGDE), poly(ethylene glycol) diglycidyl ether (PEGDE), or dicumyl peroxide (DCP). In one embodiment, about 0.1 w / w% to about 15 w / w% of the crosslinker is added based on the total dry weight of the crosslinker, and the polymer is added when blending the components (in one example, about 1% to about 10%). During the curing process, substantially all of the crosslinker is believed to react, leaving substantially no detectable unreacted crosslinker in the final film.

[0106] The polymers disclosed herein can be formulated into a mixture that can be drawn into a film or applied to a surface using any method known in the art (e.g., spraying, painting, dip coating, vapor deposition, molding, 3D printing, lithographic techniques (e.g., photolithography), micro- and nano-pipetting printing techniques, silk screen printing, etc.). The mixture can then be cured at elevated temperatures (e.g., 50-150°C). Other suitable curing methods can include, for example, ultraviolet or gamma irradiation. Biointerface Domain

[0107] The biointerface layer is a domain or layer of an implantable device configured to interface (i.e., contact) with biological fluids when implanted or connected to a host (e.g., via an intravascular access device that provides intracorporeal access to blood vessels). When present on an analyte sensor, e.g., a continuous analyte sensor implanted in a host, the biointerface layer can increase the sensor's lifespan and reduce sensor inaccuracies by reducing biomaterial-associated inflammatory responses. The antifouling properties of the biointerface layer can inhibit the accumulation of cells, proteins, and other biological species on the sensor. In some embodiments, the biointerface domain can be formed of a biointerface domain described in U.S. Provisional Application No. 62 / 273,142, filed December 30, 2015, which is incorporated herein by reference in its entirety.

[0108] The biointerface layer disclosed herein is mechanically robust, preventing damage during implantation and can withstand degradation during sensor implantation. Furthermore, the disclosed biointerface layer does not affect the response time of the sensor or the properties of the diffusion resistance layer. The disclosed biointerface layer can also be hydrophilic, which can have a large amount of water absorption, fast water absorption, and rapid stabilization, thereby not adversely affecting the start-up of the sensor. The disclosed biointerface layer is also permeable to analytes (e.g., glucose) but prevents protein adsorption.

[0109] Some embodiments described herein may include a membrane that includes a biointerface layer 48 (see Figures 2A and 2B).

[0110] Additionally, the disclosed biointerface layers can be host to pharmaceutical or bioactive agents that, upon release from the biointerface layer into local tissue, can effectively reduce or delay inflammation. Anti-inflammatory agents can be steroidal or non-steroidal drugs and can be scavengers of reactive oxygen species (ROS). Suitable anti-inflammatory agents include, but are not limited to, nonsteroidal anti-inflammatory drugs (NSAIDS), such as acetomethaphine, aminosalicylic acid, aspirin, celecoxib, choline magnesium trisalicylate, diclofenac potassium, diclofenac sodium, diflunisal, etodolac, fenoprofen, flurbiprofen, ibuprofen, indomethacin, interleukin (IL)-10, IL-6 muteins, anti-IL-6 iNOS inhibitors (e.g., L-NAME or L-NMDA), interferons, ketoprofen, ketorolac, leflunomide, melenamic acid, mycophenolic acid, mizoribine, nabumetone, naproxen, naproxen sodium, oxaprozin, Piroxicam, rofecoxib, salsalate, sulindac, and trimethine; and corticosteroids such as cortisone, hydrocortisone, methylprednisolone, prednisone, prednisolone, betamethasone, beclomethasone dipropionate, budesonide, dexamethasone sodium phosphate, flunisolide, fluticasone propionate, paclitaxel, tacrolimus, tranilast, triamcinolone acetonide, betamethasone, fluocinolone, betamethasone dipropionate, betamethasone valerate, desonide, desoximethasone, fluocinolone, triamcinolone, triamcinolone acetonide, clobetasol propionate, and dexamethasone.

[0111] In some embodiments, the biointerface layer may include a polymer described as a bioprotective layer in U.S. Patent Publication No. 2014-0094671, which is incorporated by reference herein for its teachings regarding at least bioprotective layers in sensor membranes.

[0112] In other embodiments, the biointerface layer may include a biointerface polymer. The biointerface polymer is a polyzwitterion. A polyzwitterion is a polymer in which the repeat units of the polymer chain are zwitterionic moieties. As such, these polymers have an equal number of cationic and anionic groups due to each zwitterionic repeat unit having both positive and negative charges, and therefore often an overall zero charge over a wide pH range.

[0113] Polyzwitterions are distinguished from other polyampholytes in that they contain anionic and cationic groups, but the ionic groups are not correlated with each other as part of the same repeating unit. Thus, the anionic and cationic groups may be randomly spaced apart from each other, or there may be more of one ionic group than the other. Thus, it is typical for polyampholytes to have a net charge, except perhaps over a somewhat narrow pH range.

[0114] The disclosed polyzwitterions can have a variety of repeat units exemplified as i) to vii) below, where n is an integer between 2 and 1000.

[0115] [ka]

[0116] In structures i-iv), the zwitterionic units are attached to the backbone (~~~~) and the charges are on side groups suspended from the chain. In structures v)-vii), the zwitterionic units are such that one or both charges are on the chain itself.

[0117] Examples of suitable zwitterionic monomers that can be used to generate polyzwitterions of any of structures i)-vii) include: Included are ammoniophosphates (phosphobetaines or lecithin analogs), ammoniophosphonates (phosphonobetaines), or ammoniophosphinates (phosphinobetaines), each having the structure:

[0118] [ka]

[0119] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 , R 3 , and R 4 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R 3 , R 4 and one or more of Z are substituted with a polymerizable group.

[0120] "Polymerization group" means a functional group that allows the polymerization of a monomer with itself to form a homopolymer or with a different monomer to form a copolymer. Depending on the type of polymerization method used, the polymerization group may be selected from alkenes, alkanes, epoxides, lactones, amines, hydroxyls, isocyanates, carboxylic acids, anhydrides, silanes, halides, aldehydes, and carbodiimides. In step-growth polymerizations, matching pairs of functional groups may be selected to facilitate polymerization, for example, to polymerize dihydroxyl groups bearing zwitterionic monomers, and comonomers containing diisocyanate, epoxide, or dicarboxylic acid groups may be selected to provide polymers formed with urethane, ether, and ester linkages.

[0121] Further examples of suitable zwitterionic monomers that can be used to generate polyzwitterions of any of structures i)-vii) include ammoniosulfonates (sulfobetaines), ammoniosulfates, each having the following structure:

[0122] [ka]

[0123] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 and R 3 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R 3 and one or more of Z are substituted with a polymerizable group; Ammoniocarboxylates have the structure:

[0124] [ka]

[0125] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 and R 3 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R3 and one or more of Z are substituted with a polymerizable group.

[0126] In each of these monomers, Z can have a length of 1 to 12 atoms, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 atoms, and any of these values ​​can form the upper or lower endpoints of a range.

[0127] These monomers can be prepared by methods known to those of skill in the art, for example, as detailed in Laschewsky, "Structures and synthesis of zwitterionic polymers," Polymers 6:1544-1601, 2014. In certain examples, the disclosed polyzwitterions can have repeating zwitterionic units derived from any of the zwitterionic monomers disclosed above.

[0128] The biointerface polymer may also include polyurethane and / or polyurea segments. For example, the biointerface polymer may include polyurethane copolymers such as polyether-urethane-urea, polycarbonate-urethane, polyether-urethane, silicone-polyether-urethane, silicone-polycarbonate-urethane, polyester-urethane, polyurethane-urea, etc. These polyurethane and / or polyurea segments are referred to herein as "hard segments" because they contain urea and / or urethane linkages formed from polyisocyanates and short chain polyols or polyamines, moieties that are rich in hydrogen bonds. These segments may also be relatively hydrophobic.

[0129] In addition to the polyurethane and / or polyurea hard segments, the disclosed biointerface polymers may also include soft segments that have relatively poor hydrogen bonding. The soft segments are typically composed of polyols such as polycarbonates, polyesters, polyethers, polyarylenes, and polyalkylenes. The soft segments can be either hydrophobic or hydrophilic.

[0130] Biointerface polymers useful in certain embodiments may include linear or branched polymers on the backbone structure of the polymer. Thus, either the hard or soft segments may include a branched or linear backbone.

[0131] Zwitterionic monomers, as described herein, can be part of either the hard or soft segments, or both.

[0132] In some embodiments, the hard segment portion of the biointerface polymer may comprise about 5% to about 50% by weight of the polymer, sometimes about 15% to 20% by weight, and other times about 25% to 40% by weight. The hard segment may have a molecular weight of about 160 daltons to about 10,000 daltons, and sometimes about 200 daltons to about 2,000 daltons. In some embodiments, the molecular weight of the soft segment may be about 200 daltons to about 10,000,000 daltons, and sometimes about 500 daltons to about 5,000 daltons, and sometimes about 500 daltons to about 2,000 daltons.

[0133] As stated, the hard segment can be a polyurethane or a polyurea. Polyurethanes are polymers produced by the condensation reaction of diisocyanates and difunctional hydroxyl-containing materials. Polyureas are polymers produced by the condensation reaction of diisocyanates and difunctional amine-containing materials. Preferred diisocyanates include aliphatic diisocyanates containing from about 4 to about 9 methylene units. Cycloaliphatic moieties containing diisocyanates can also be useful in preparing the polymer and copolymer components of the membranes of the preferred embodiments.

[0134] The soft segments used in preparing the biointerface polymers may be polyfunctional aliphatic polyols, polyfunctional aliphatic or aromatic amines, etc., which may be useful in effecting permeability of the analyte (e.g., glucose) therethrough, and may include, for example, polyoxazolines, poly(ethylene glycol)s (PEGs), polyacrylamides, polyimines, polypropylene oxides (PPOs), PEG-co-PPO diols, silicone-co-PEG diols, silicone-co-PPO diols, polyethyl acrylates (PEAs), polyvinylpyrrolidones (PVPs), and modifications thereof (e.g., PVP vinyl acetate), where PEGs and modifications thereof may be preferred due to their hydrophilicity.

[0135] In some embodiments, the soft segment portion of the biointerface polymer may comprise about 5% to about 50%, sometimes about 15% to 20%, and other times about 25% to 40% by weight of the polymer. The soft segment may have a molecular weight of about 160 daltons to about 10,000 daltons, and sometimes about 200 daltons to about 2,000 daltons. In some embodiments, the molecular weight of the soft segment may be about 200 daltons to about 10,000,000 daltons, sometimes about 500 daltons to about 5,000 daltons, and sometimes about 500 daltons to about 2,000 daltons.

[0136] In some embodiments, a biointerface polymer comprising hard and soft segments, and zwitterionic repeat units, can have a molecular weight of from about 10 kDa to about 500,000 kDa, e.g., from about 10 kDa to about 100,000 kDa, from about 1000 kDa to about 500,000 kDa, from about 10,000 kDa to about 100,000 kDa, and from about 100,000 kDa to about 500,000 kDa.

[0137] The hard and soft segments may each be selected for their properties, such as, but not limited to, tensile strength, flex life, modulus, etc. For example, polyurethanes are relatively strong and offer many reaction pathways, properties which may be advantageous as bulk properties for the membrane domain of a continuous sensor.

[0138] As stated, the biointerface polymers contain one or more zwitterionic repeat units, and thus these groups are "internal" with respect to the polymer backbone. Such "internal" repeat units are distinguished from materials found at the ends of polymer chains, since such moieties are only attached to the polymer chain at one position. Although the disclosed biointerface polymers may, in some embodiments, have zwitterionic groups at the ends of the polymer chains, such groups are not the only zwitterionic groups in the chain, and there is at least one internal zwitterionic group in the backbone.

[0139] In some preferred embodiments, the zwitterionic moieties are selected for desirable properties, such as, for example, non-stationary noise blocking ability, intermittency (reduced), ability to repel charged species, cationic or ionic blocking, surface wettability, anti-fouling properties, etc. In some embodiments, the zwitterions or zwitterionic precursors are present as zwitterionic groups while the device is in vivo. As such, these groups present a mixed charge area of ​​the device surface to the surrounding environment, thereby increasing surface hydration of the device and potentially reducing non-specific protein adsorption and cell attachment.

[0140] In some embodiments, the biointerface polymer comprises at least about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about In some embodiments, the zwitterionic repeat units comprise about 28%, about 29%, about 30% to about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, or about 55% by weight of zwitterionic repeat units.

[0141] The zwitterionic repeat units may be betaines, precursors or derivatives thereof (e.g., alkyl or amino betaines), such as carboxyl, sulfo, or phosphobetaine compounds. These segments or moieties may be incorporated into the biointerface polymer in the hard segments, soft segments, or both, for example, up to about 55% by weight of the biointerface polymer.

[0142] In some embodiments, two or more different zwitterionic or zwitterionic precursor segments or moieties are used, while in other embodiments, a single zwitterionic or zwitterionic precursor segment or moiety may be used in the biointerface polymer.

[0143] Some examples of biointerface polymers are illustrated diagrammatically in FIG. 12. In general, biointerface polymers include one or more hard segments and one or more soft segments. The hard segments can be aliphatic or aromatic monomers. The soft segments can be hydrophilic or hydrophobic oligomers, such as polyalkylene glycols, polycarbonates, polyesters, polyethers, polyvinyl alcohols, polyvinylpyrrolidones, polyoxazolines, and the like. Zwitterionic groups (e.g., betaines) can be part of the soft segment, the hard segment, or both. As illustrated in FIG. 12, a variety of hard and soft segments can be present, which allows for tuning of the properties of the biointerface polymer by using different segments, different segment lengths, functionalization of certain segments, crosslinking of certain segments, and the like. In some embodiments, biocompatible segmented block polyurethane copolymers including hard and soft segments can be used for the biointerface layer.

[0144] Incorporation of these zwitterionic repeat units into a polymer can be accomplished by using zwitterionic monomers that have a diol or diamine (e.g., at the Z position) or R 1 ~R 4 The diol or diamine may be attached at any of R 1 ~R 4 Attachment to a diol or diamine in can be achieved by reacting the corresponding precursor with a halo-substituted diamine or diol. Examples of such monomers are shown below:

[0145] [ka]

[0146] wherein W, Y, and Z are independently branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl, any of which may be optionally substituted with O, OH, halogen, amino, or alkoxyl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 2 , R 3 , and R 4 is independently selected from alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl. In certain examples, W is C1-C4 alkyl. In certain examples, Y is C1-C4 alkyl. In other examples, Z is C1-C4 alkyl.

[0147] These compounds can be reacted with diisocyanates to form polyurethanes or polyureas. Alternatively, the carboxylate, sulfonate, phosphinate, or phosphonate moieties can be protected and then the protecting groups removed after polymerization. In another alternative, the amines can be tertiary amines and then quaternized by alkylation after polymerization.

[0148] Another method involves the radical polymerization of zwitterionic monomers having unsaturation substituted at the Z position in the monomers shown above. In another example, zwitterionic monomers in which the unsaturation is attached to an ammonium group can be used in the radical polymerization. Examples of such monomers are shown below:

[0149] [ka]

[0150] In the formula, X is O, NH, or NR 4Y and Z are independently branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl, any of which may be optionally substituted with OH, halogen, or alkoxyl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 3 and R 5 is independently selected from heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl. In certain examples, R 5 is H or CH3. In other examples, X is O. In yet other examples, X is NH or NCH3. In particular examples, Y is C1-C4 alkyl. In other examples, Z is C1-C4 alkyl.

[0151] Additional examples of suitable zwitterionic monomers include N-(2-methacryloyloxy)ethyl-N,N-dimethylammoniopropanesulfonate, N-(3-methacryloylimino)propyl-N,N-dimethylammoniopropanesulfonate, 2-(methacryloyloxy)ethylphosphatidylcholine, and 3-(2′-vinyl-pyridino)propanesulfonate.

[0152] In other embodiments, the biointerface polymer is crosslinked. For example, polyurethaneurea polymers having aromatic or aliphatic segments with electrophilic functional groups (e.g., carbonyl, aldehyde, anhydride, ester, amide, isocyanate, epoxy, allyl, or halo groups) can be crosslinked with crosslinkers having multiple nucleophilic groups (e.g., hydroxyl, amine, urea, urethane, or thio groups). In further embodiments, polyurethaneurea polymers having aromatic or aliphatic segments with nucleophilic functional groups can be crosslinked with crosslinkers having multiple electrophilic groups. Still further, polyurethaneurea polymers having hydrophilic segments with nucleophilic or electrophilic functional groups can be crosslinked with crosslinkers having multiple electrophilic or nucleophilic groups. Unsaturated functional groups on the polyurethaneurea can also be used for crosslinking by reacting with multivalent free radical agents.

[0153] Non-limiting examples of suitable crosslinkers include isocyanates, carbodiimides, glutaraldehyde or other aldehydes, aziridines, silanes, epoxies, acrylates, free radical agents, ethylene glycol diglycidyl ether (EGDE), poly(ethylene glycol) diglycidyl ether (PEGDE), or dicumyl peroxide (DCP). In one embodiment, about 0.1 w / w% to about 15 w / w% of the crosslinker is added based on the total dry weight of the crosslinker, and the polymer is added when blending the components (in one example, about 1% to about 10%). During the curing process, substantially all of the crosslinker is believed to react, leaving substantially no detectable unreacted crosslinker in the final layer.

[0154] Additionally, the disclosed biointerface layer may have zwitterions trapped or embedded within the polymer network by non-covalent interactions. Thus, in further embodiments, the disclosed biointerface layer may include a biointerface polymer and an additional betaine blended therewith. For example, the biointerface polymer may be blended with cocamidopropyl betaine, oleamidopropyl betaine, octyl sulfobetaine, caprylyl sulfobetaine, lauryl sulfobetaine, myristyl sulfobetaine, palmityl sulfobetaine, stearyl sulfobetaine, betaine (trimethylglycine), octyl betaine, phosphatidylcholine, glycine betaine, poly(carboxybetaine) (pCB), and poly(sulfobetaine) (pSB). It will be understood that many more zwitterionic compounds or precursors or derivatives thereof may be applicable, and that this list of exemplary betaines is not intended to limit the scope of the embodiments.

[0155] The biointerface layer may further include a domain comprising a surface-modifying polymer added to a base polymer, where the surface-modifying polymer comprises a polymer chain having both hydrophilic and hydrophobic regions, and where the one or more zwitterionic compounds are covalently attached to an interior region of the polymer, and the base polymer may be selected from silicones, epoxies, polyolefins, polystyrenes, polyoxymethylenes, polysiloxanes, polyethers, polyacrylics, polymethacrylics, polyesters, polycarbonates, polyamides, poly(etherketones), poly(etherimides), polyurethanes, and polyurethaneureas.

[0156] In some embodiments, the biointerface layer may comprise a combination of one or more biointerface polymer(s), e.g., polyurethane or polyurethane urea and one or more hydrophilic polymers, e.g., PVA, PEG, polyacrylamide, polyacetate, polyzwitterion, PEO, PEA, PVP, and variations thereof (e.g., PVP vinyl acetate), e.g., as a physical blend or admixture, where each polymer maintains its inherent chemical properties.

[0157] In some embodiments, the biointerface layer 48 is positioned most distal to the sensing region such that its outermost domain contacts biological fluids when inserted in vivo. In some embodiments, the biointerface layer may be constructed of a material that is resistant to cell attachment, impermeable to cells, and biostable. Without being bound by theory, if the biointerface domain 48 is resistant to cell attachment (e.g., attachment by inflammatory cells such as macrophages, and thus is kept at a sufficient distance from other domains, e.g., enzyme domains), hypochlorite and other oxidizing species are short-lived species in vivo and biodegradation generally does not occur. Furthermore, preferred materials for forming the biointerface domain 48 are referred to as biodurable because they may be resistant to the effects of these oxidizing species. In some embodiments, the biointerface domain controls the flux of oxygen and other analytes (e.g., glucose) to the underlying enzyme domain (e.g., the functionality of the diffusion resistance domain is incorporated into the biointerface domain, such that a separate diffusion resistance domain is not required).

[0158] In some embodiments, the one or more zwitterionic compounds or precursors thereof applied to the surface of the membrane system are hydrolyzable cationic esters of zwitterionic compounds. In these embodiments, the hydrolyzable cationic esters provide the added benefit that hydrolysis of the cationic ester to a non-fouling zwitterionic group may kill microorganisms (such as bacteria) or condense DNA. Furthermore, the mixed charge nature of the resulting zwitterionic group results in inhibition of non-specific protein adsorption on the surface of the sensor. In these embodiments, cationic betaine esters, such as cationic pCB esters, are preferred.

[0159] In certain embodiments, the biointerface polymer may include reactive groups that may be available for further functionalization. For example, unsaturated functional groups such as alkynes may be used to attach various moieties attached to dipolar groups such as azides to various moieties to form covalent bonds. Such Huisgen cycloaddition chemistry is often referred to as click chemistry. Thus, in certain embodiments herein, the biointerface layer may include alkyne functional groups pendant to the polymer backbone. Antiseptics, cytokines, anti-inflammatory agents, steroids, and other bioactive agents disclosed herein, such as proteins, attached to dipolar groups such as azides, may be conveniently attached to the polymer, resulting in triazole groups. Thus, biointerface layers, sensors including such layers that include alkynes, triazoles, or both, are disclosed herein. These reactive groups may be present in the zwitterionic repeat unit (e.g., as substituents on Z or Y).

[0160] Incorporating zwitterion or zwitterion precursor segments or moieties into the polymer backbone can be difficult due to solubility issues associated with the zwitterion or zwitterion precursor monomers. Such groups can typically only be dissolved in highly polar solvents such as methanol and water, which are unfavorable for the synthesis of some biointerface polymers (e.g., polyurethanes). Thus, the available functional groups that can be chemically incorporated into the backbone of biointerface polymers and used by solution-based polycondensation synthesis are limited. As an alternative method of incorporating zwitterion or zwitterion precursor segments or moieties into the backbone of a base polymer, precursors or derivatives of the zwitterion or zwitterion precursor can be used. For example, zwitterion precursors and / or zwitterion derivatives with more desirable solubility characteristics in low polarity organic solvents can be used as monomers. Biointerface polymers (e.g., polyurethaneureas) can be synthesized by polycondensation reactions to form well-defined polymers with high molecular weights and low polydispersity indexes. These polymers can then be converted into zwitterionic group containing polymers via chemical reactions (hydrolysis, deprotection, thermally induced rearrangement, and UV induced degradation) or biologically induced reactions after in vivo implantation of the device.

[0161] In certain embodiments, the thickness of the biointerface domain can be about 0.1, about 0.5, about 1, about 2, about 4, about 6, about 8 μm or less to about 10, about 15, about 20, about 30, about 40, about 50, about 75, about 100, about 125, about 150, about 175, about 200, or about 250 μm or more. In some of these embodiments, the thickness of the biointerface domain can sometimes be about 1 to about 5 μm, and sometimes about 2 to about 7 μm. In other embodiments, the biointerface domain can be about 20 or about 25 μm to about 50, about 55, or about 60 μm thick. In some embodiments, the glucose sensor can be configured for transdermal or short-term subcutaneous implantation and can have a thickness of about 0.5 μm to about 8 μm, and sometimes about 4 μm to about 6 μm. In one glucose sensor configured for fluid communication with the host's circulatory system, the thickness can be from about 1.5 μm to about 25 μm, and sometimes from about 3 to about 15 μm. In some embodiments, the biointerface layer or any other layer of the electrode can have a consistent thickness, while in other embodiments, it is contemplated that the thickness can vary. For example, in some embodiments, the thickness of the biointerface layer can vary along the longitudinal axis of the electrode end.

[0162] The biointerface layer can be hydrophilic as measured by contact angle, for example, the biointerface layer can have a contact angle of about 20° to about 90°, about 60° to about 90°, about 70° to about 90°, about 80° to about 90°, about 60° to about 80°, at least about 50°, at least about 60°, or at least about 70°.

[0163] The biointerface layer may also have a low polydispersity index, for example, the polymer may have a polydispersity index of about 1.4 to about 3.5, about 1.75 to about 2.25, about 1.75 to about 2.5, or about 2.

[0164] The biointerface layer also cannot substantially affect the T95 response time of the sensor. The T95 response time is the amount of time required for the electrical response to reach 95% difference between the response of the first glucose step and the response of the second glucose step. For example, a sensor having a biointerface layer disclosed herein may have a T95 response time that is the same as or within 5% of the T95 response time of an otherwise identical sensor without the biointerface layer.

[0165] Diffusion Resistance Domain One drawback of some current diffusion-resistant layers is that they tend to cause significant sensor drift within a few days of sensor use, as shown by both in vitro testing and in vivo data. Without wishing to be bound by theory, sensitivity is in part related to the hydrophilic polymer in the diffusion-resistant layer. If the hydrophilic polymer leaches out of the layer over time under hydrated conditions, changes in sensitivity and reduced accuracy and lifetime can result.

[0166] Furthermore, non-equilibrium phase separation between these two polymers can lead to unpredictable sensitivity changes over time, requiring additional calibration during sensor use. Calibrated, reproducible phase separation between hydrophilic and hydrophobic polymers improves sensor accuracy, consistency and reproducibility, as well as sensor lifetime.

[0167] The diffusion-resistant membrane also requires strong mechanical stability to resist friction against tissue in vivo and keep the phase-separated microstructure intact. A strong mechanically resistant layer can also minimize membrane rearrangement, improve sublayer stability (by increasing hoop strength), and reduce tip rupture failure (by improving puncture resistance).

[0168] A stable semi-permeable diffusion-resistant layer is disclosed herein. The disclosed diffusion-resistant layer includes a base polymer that can provide a structurally stable matrix. The disclosed diffusion-resistant layer also includes a hydrophilic analyte-permeable phase present throughout the layer. The layer has a microphase-separated morphology in which the analyte-permeable phase is permeated throughout the primary hydrophobic polymer matrix. The primary matrix polymer provides the structural support required by the membrane application, as well as the influence on the size and distribution of the analyte-permeable phase separation, its microstructure. It is the size and distribution of the analyte-permeable phase that determines the permeability, and therefore the sensitivity, of a given electrochemical sensor. Therefore, it is understandable and desirable to maintain the size and distribution of the analyte-permeable phase during initial deployment to minimize sensitivity changes over time of use and to resist temperature and mechanical stress variations.

[0169] In certain embodiments, the disclosed diffusion resistant layer comprises a polymer blend consisting of a base polymer that is a hydrophobic segmented block copolymer and a hydrophilic polymer. The hydrophobic segmented block copolymer has a high glass transition temperature (T g ) High T g By using a polymer having a .mu.m or less hydrophilic .alpha.-hydroxypropyltrimethoxysilane, a more rigid matrix can be formed, limiting hydration-induced swelling and maintaining the size and distribution of the hydrophilic analyte-permeable microphases.

[0170] At low temperatures, polymers are in a brittle glassy state because there is not enough energy to drive local or segmental motion of the chains. As the temperature is increased, at some point, enough energy becomes available to allow some chain movement. For polymers that contain both amorphous and crystalline phases, or are exclusively amorphous, this segmental movement of chains relative to the amorphous segments occurs at a temperature called the glass transition temperature (T g). The presence of unoccupied volume in the amorphous polymer phase results in some degree of segmental chain motion. This segmental motion of the chains is sometimes described as a snake sliding "in place" within the glass. Localized motion of the chains causes a further increase in the unoccupied volume, and larger segments can eventually move, allowing further motion of the snake within the glass. A further increase in temperature can provide enough energy to disrupt the crystalline phase, which is often referred to as the melting transition temperature (T m In gas and liquid separation membranes, mass transfer occurs within the amorphous phase.

[0171] The flexibility of amorphous polymers is determined by their characteristic transition temperature (T g ) is significantly reduced. g At temperatures below 100° C., there is no ready segmental motion, and therefore polymers with desirable glass transition temperatures are selected for applications that limit segmental motion and provide structural and dimensional stability. g The value of T is best associated with the onset of segmental motion in the principle polymer backbone; the stiffer and bulkier the polymer segments are, the higher the T g In multiblock urethane copolymers, multiple T g , e.g., a very low T of -120°C g This can occur when silicone is used as the co-soft segment. Similarly, a relatively high T of -50°C or higher can be present. g may be related to the stiffer polycarbonate co-soft segments.

[0172] The glass transition temperature of the hydrophobic segmented block copolymer component of the diffusion resistant layer may be measured using ASTM D3418. In certain examples, the minimum glass transition temperature of the hydrophobic segmented block copolymer may be greater than -50°C, e.g., greater than -40°C, greater than -30°C, greater than -20°C, greater than -10°C, or greater than 0°C. In other examples, the minimum hydrophobic segmented block copolymer may have a glass transition temperature of 0°C to -50°C, -10°C to -50°C, -20°C to -50°C, 0°C to -40°C, -10°C to -40°C, -20°C to -40°C, 0°C to -30°C, -10°C to -30°C, or 0°C to -30°C. The ... -10°C to -40°C, -20°C to -40°C, 0°C to -30°C, -10°C to -30°C, or 0°C to -30°C. g Therefore, multiple T g When present, the T g is the minimum T g As illustrated in FIG. 5, the T g can be modified by varying the amount and type of soft segment incorporated into the polyurethane block copolymer synthesis. Silicone-containing polyurethanes have a low T of about -120°C associated with silicones. g and is absent in the silicone-free polycarbonate urethane. g can be further increased by incorporating stiffer soft segments such as polycarbonate diols.

[0173] The disclosed hydrophobic segmented block copolymers may also have an ultimate tensile strength as measured by ASTM D1708 of greater than 6000 psi, e.g., greater than 8000 psi, greater than 8250 psi, greater than 8500 psi, or greater than 8750 psi. For example, the hydrophobic segmented block copolymers may have an ultimate tensile strength of 7900-8750 psi, 8250-8750 psi, 8500-8700 psi, or 7900 psi-8250 psi.

[0174] In some embodiments, the base polymer can be synthesized to include a polyurethane membrane having both hydrophilic and hydrophobic regions to control the diffusion of glucose and oxygen to the analyte sensor. A suitable hydrophobic polymer component can be a polyurethane or a polyether urethane urea. Polyurethanes are polymers produced by the condensation reaction of diisocyanates and difunctional hydroxyl-containing materials. Polyureas are polymers produced by the condensation reaction of diisocyanates and difunctional amine-containing materials. Preferred diisocyanates include aliphatic diisocyanates containing about 4 to about 8 methylene units. Cycloaliphatic moieties containing diisocyanates can also be useful in preparing the polymer and copolymer components of the membranes of the preferred embodiments. Examples of materials that can be used to make non-polyurethane type membranes include vinyl polymers, polyethers, polyesters, polyamides, inorganic polymers (such as polysiloxanes and polycarbosiloxanes), natural polymers (such as cellulose and protein-based materials), and copolymers, mixtures, or combinations thereof.

[0175] In certain embodiments, the base polymer may be substantially free of silicone (e.g., less than 1% by weight). In another embodiment of a suitable base polymer, the hydrophilic soft segment polymer component may be polyethylene oxide. For example, one useful hydrophilic copolymer component is a polyurethane polymer containing about 20% hydrophilic polyethylene oxide. The polyethylene oxide portion of the copolymer is thermodynamically driven to separate from the hydrophobic portion of the copolymer and the hydrophobic polymer component. The 20% polyethylene oxide-based soft segment portion of the copolymer used to form the final blend affects water uptake and subsequent glucose permeability of the membrane. In this case, the minimum T of the polymer domain formed by the hydrophobic soft segment of the hard segment is the minimum T of the hydrophobic soft segment of the hard segment. g is above -50°C.

[0176] Having a homogeneous segmented block copolymer can help ensure that the hydrophilic segments are more evenly distributed throughout the diffusion resistance layer. The phase separation characteristics of the membrane (or controlled location of hydrophilic / hydrophobic regions for the creation of membrane permeation channels) can be further controlled by altering the size and length of the monomers / oligomers involved in the membrane synthesis. In this embodiment, only one polymer is used in the resistance layer, minimizing the sensitivity change of the leaching hydrophilic polymer.

[0177] Alternatively, in some embodiments, the diffusion-resistant layer may include a combination or blend of a base polymer (e.g., a segmented polyurethane block copolymer disclosed herein) with one or more hydrophilic polymers (e.g., PVA, PEG, polyacrylamide, acetate, PEO, PEA, PVP, POX, and copolymers, blends, and / or variations thereof). Any of a variety of polymer combinations may be used to provide the desired blend of glucose, oxygen, and interference permeability properties. The hydrophilic polymer may be blended with the base polymer or covalently bonded to the base polymer.

[0178] When a hydrophilic polymer is covalently bonded to the base polymer, one way to make an aqueous dispersion is to dissolve the polymer in acetone and add this solution dropwise to an aqueous solvent and mix at high shear rates. The aqueous solvent can be distilled water, or water with water soluble stabilizing additives such as PVP, salts, or SDS. Although either variant can be used, one example of a diffusion resistant layer uses an aqueous dispersion with either an aqueous solvent of PVP in water (0-50% PVP) at the PVP concentration that results in the desired sensor sensitivity, or a pure water solvent to which a concentrated PVP solution can be added after the dispersion is made.

[0179] In some specific embodiments, a triblock polymer of PVP can be used as the hydrophobic polymer in the diffusion-resistant layer. In yet another example, the hydrophilic polymer can be PVP functionalized with silane, alcohol, fluorine, or acrylate. In yet another example, silica or similar nanocomposite material can be used in the blend instead of or in addition to the hydrophilic polymer. Thus, for example, the diffusion-resistant layer can be formed from a blend of a hydrophobic block copolymer, such as the polycarbonate-urethane-based polymer disclosed herein, with silica or a nanocomposite.

[0180] In yet a further example, the hydrophilic polymer can be crosslinked, for example, with a vinyl lactam. In one particular example, a crosslinked polyvinylpyrrolidone (PVP) polymer can be made by reaction of an epoxide-containing PVP copolymer with a tertiary amine-containing PVP copolymer in solution at a given temperature. (a) 80-99 wt% vinylpyrrolidone (VP) and 1-20 wt% tertiary amine-containing polymerizable monomer, such as vinylimidazole (VI) or 4-vinylpyridine (VPy), and (b) a crosslinkable copolymer of 80-99 wt% VP and 1-20 wt% epoxide-containing polymerizable monomer, such as allyl glycidyl ether (AGE) or glycidyl acrylate (GA), reacted in solution, such as water, alcohol, or mixtures thereof, at a temperature, such as 50° C. to 70° C., in an (a):(b) weight ratio (solids basis) of about 2:1 to 1:2, preferably about 1:1 (each at about 10-30% solution concentration), to provide a crosslinked PVP product. In another example, the diffusion-resistant layer can be formed from a blend of a hydrophobic block copolymer, such as a polycarbonate-urethane-based polymer disclosed herein, with crosslinked PVP and / or PVP functionalized with silane, alcohol, or fluorine.

[0181] In some embodiments, the diffusion-resistant layer may be formed from a blend of a polycarbonate-urethane-based polymer and a PVP hydrophilic polymer as disclosed herein. In some of the embodiments involving the use of PVP, the PVP portion of the polymer blend may comprise about 5% to about 50%, sometimes about 15% to about 20%, and other times about 25% to about 40% by weight of the polymer blend. It is contemplated that PVP of various molecular weights may be used. For example, in some embodiments, the molecular weight of the PVP used may be about 25,000 Daltons to about 5,000,000 Daltons, sometimes about 50,000 Daltons to about 2,000,000 Daltons, and other times about 6,000,000 Daltons to about 10,000,000 Daltons. The same percentages may apply when using POX instead of PVP.

[0182] In some other embodiments, the base polymer can be end-capped with groups that can be used to link polymers together (so-called networking moieties) and groups that can bloom to surfaces and affect surface properties (so-called blooming moieties). These are shown in the schematic diagrams below, where Figure 1 is the blooming moiety and Figure 2 is the networking moiety.

[0183] [ka]

[0184] It is also contemplated that the blooming moiety and the networking moiety can be the same, as shown in Scheme 2, where the blooming moiety and the networking moiety are siloxanes.

[0185] [ka]

[0186] In other examples, the networking moiety and the blooming moiety are different, as shown below in Scheme 3, where the blooming moiety is a tris(trimethylsilyl)siloxane and the networking moiety is a methacrylamide, or in Scheme 4, where the blooming moiety is a tris(trimethylsilyl)siloxane and the networking moiety is a carboxylic acid.

[0187] [ka]

[0188] [ka]

[0189] Further examples of blooming moieties are fluorocarbons. Further examples of networking moieties are vinyl groups (e.g., vinyl alcohol, vinylbenzyl), isocyanates, amines, amides, alcohols, azides, thiols, alkenes, alkynes, esters, etc. In some other embodiments, the networking moiety can be a group that complexes with iron (Fe(II) or Fe(III)).

[0190] Furthermore, the disclosed diffusion-resistant layer may have zwitterions trapped or embedded in the polymer network by non-covalent interactions. Thus, in further embodiments, the disclosed diffusion-resistant layer may include a base polymer and a hydrophilic polymer and an additional betaine blended therewith. For example, the diffusion-resistant layer may be blended with cocamidopropyl betaine, oleamidopropyl betaine, octyl sulfobetaine, caprylyl sulfobetaine, lauryl sulfobetaine, myristyl sulfobetaine, palmityl sulfobetaine, stearyl sulfobetaine, betaine (trimethylglycine), octyl betaine, phosphatidylcholine, glycine betaine, poly(carboxybetaine) (pCB), and poly(sulfobetaine) (pSB). It will be understood that many more zwitterionic compounds or precursors or derivatives thereof may be applicable, and that this list of exemplary betaines is not intended to limit the scope of the embodiments.

[0191] Sensors including the disclosed diffusion resistance layers can have minimal drift (e.g., 10% or less) over time. For example, sensors are disclosed herein that have less than 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, or 1% drift over a 10 day period.

[0192] The sensor with the diffusion resistance layer is shown as 46 in Figures 2A and 2B and is located closer to the implantable device than the biointerface layer. In some embodiments, the functionality of the diffusion resistance domain may be incorporated into the biointerface layer. Therefore, it should be noted that the description herein of the diffusion resistance domain may also apply to the biointerface layer. The diffusion resistance domain functions to control the flux of oxygen and other analytes (e.g., glucose) to the underlying enzyme domain.

[0193] The diffusion resistance domain 46 includes a semi-permeable membrane that controls the flux of oxygen and glucose to the underlying enzyme domain 42, preferably with a non-rate-limiting excess of oxygen. As a result, the upper limit of linearity of glucose measurement is extended to values ​​much higher than would be achieved without the diffusion resistance domain. In some embodiments, the diffusion resistance domain exhibits an oxygen-to-glucose permeability ratio of approximately 200:1, while in other embodiments the oxygen-to-glucose permeability ratio may be approximately 100:1, 125:1, 130:1, 135:1, 150:1, 175:1, 225:1, 250:1, 275:1, 300:1, or 500:1. As a result of the high oxygen-to-glucose permeability ratio, one-dimensional reactant diffusion can provide sufficient excess oxygen at all reasonable glucose and oxygen concentrations found in the subcutaneous matrix (see Rhodes et al., Anal. Chem., 66:1520-1529 (1994)). In some embodiments, a lower oxygen to glucose ratio may be sufficient to provide excess oxygen by using a high oxygen solubility domain (e.g., silicone material) to enhance oxygen supply / transport to the enzyme membrane or electroactive surface. By using a silicone composition to enhance oxygen supply, for example, glucose concentration is less of a limiting factor. In other words, if more oxygen is supplied to the enzyme or electroactive surface, then more glucose can also be supplied to the enzyme without resulting in an excess of oxygen rate limitation.

[0194] In some embodiments, the diffusion resistance layer 46 may be formed as a unitary structure with the biointerface domain 48, i.e., the inherent properties of the diffusion resistance domain 46 are incorporated into the biointerface domain 48 such that the biointerface domain 48 functions as the diffusion resistance domain 46.

[0195] In certain embodiments, the thickness of the diffusion resistance domain can be about 0.05 μm or less to about 200 μm or more. In some of these embodiments, the thickness of the diffusion resistance domain can be about 0.05, about 0.1, about 0.15, about 0.2, about 0.25, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 1, about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 6, about 8 μm to about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 19.5, about 20, about 30, about 40, about 50, about 60, about 70, about 75, about 80, about 85, about 90, about 95, or about 100 μm. In some embodiments, the thickness of the diffusion resistance domain is from about 2, about 2.5, or about 3 μm to about 3.5, about 4, about 4.5, or about 5 μm for percutaneously implanted sensors, or from about 20 or about 25 μm to about 40 or about 50 μm for fully implanted sensors.

[0196] In some embodiments, the diffusion resistance layer may be deposited by spraying or dip coating. In one exemplary embodiment, the diffusion resistance layer is formed by dip coating the sensor in the diffusion resistance layer solution using an insertion speed of about 0.5 in / min to about 60 in / min, sometimes about 1 in / min, a residence time of about 0.01 minutes to about 2 minutes, sometimes about 1 minute, and a withdrawal speed of about 0.5 in / min to about 60 in / min, sometimes about 1 in / min, and curing (drying) the domain for about 1 minute to about 14 hours, sometimes about 3 minutes to about 15 minutes (which may be accomplished at room temperature or under vacuum, e.g., about 20 to about 30 mmHg). In one exemplary embodiment, a 3 minute curing (i.e., drying) time is used between the application of each layer.

[0197] In some embodiments, the dipping process can be repeated at least once up to 10 times or more. In other embodiments, only one dipping is preferred. The preferred number of repeated dipping processes may depend on the polymers used, their concentrations, the conditions during deposition (e.g., dipping), and the desired thickness, etc. In one embodiment, after the sensor is coated with the diffusion-resistant layer, the sensor is contacted with an aqueous solution (e.g., water or a buffer solution) to accelerate polymer rearrangement, reduce drift, and reduce sensor variability. The layer may then harden during hydration.

[0198] Curing of the deposited polymer layer by solvent evaporation sometimes helps prevent sensor drift by allowing the polymer chains and hydrophilic and hydrophobic components to rearrange to a lower energy state that remains stable over time. The final polymer microstructure determines the analyte and oxygen permeability characteristics and the final sensor performance. Thus, the analyte sensor can be cured such that all rearrangements occur before the sensor is calibrated and the sensor sensitivity does not change before or during use. The rate, type of rearrangement, and polymer layer microstructure can be controlled and induced by exposure to different conditions, typically humidity, temperature, and time. Aqueous solvent curing can be used to accelerate the polymer rearrangement with hydrophilic and hydrophobic domains within the polymer layer to result in a sensor with desirable stability, analyte permeability, and oxygen performance. Benefits over current humidity and temperature curing processes include reduced drift, reduced curing time, and reduced sensor-to-sensor variability.

[0199] The curing aqueous solvent contains water-miscible solvents, salts, stabilizers, plasticizers, or other components to modify rearrangements. The solvent temperature can range from 0°C to 100°C, more preferably from 20°C to 70°C. The miscible solvent can be an alcohol or a polar organic solvent, such as ethanol or THF. The salt can be of any type, such as PBS, and can include modifying components such as biocides and interfering species. The process involves multiple immersion steps in different aqueous formulations at different temperatures to selectively induce specific sequential rearrangements or extract specific compounds.

[0200] Enzyme domain The enzyme layer, also referred to as the enzyme domain, is a domain or layer of the implantable device configured to immobilize an active enzyme, which reacts with an analyte when implanted in or connected to a host (e.g., via an intravascular access device that provides extracorporeal access to blood vessels). In one embodiment, the enzyme domain comprises glucose oxidase. In other embodiments, the enzyme domain can be impregnated with other oxidases, such as galactose oxidase, cholesterol oxidase, amino acid oxidase, alcohol oxidase, lactate oxidase, or uricase. For example, for an enzyme-based electrochemical glucose sensor to work well, the sensor response should not be limited by enzyme activity or cofactor concentration. In some embodiments, the enzyme domain can be formed of the enzyme domain described in U.S. Provisional Application No. 62 / 273,155, filed December 30, 2015, which is incorporated herein by reference in its entirety.

[0201] The enzyme layer disclosed herein is mechanically robust, prevents physiochemical degradation upon implantation, and can withstand adhesive degradation during sensor implantation. Furthermore, the disclosed enzyme layer does not affect the response time of the sensor, which is permeable to analytes, and does not alter the glucose rate limiting control by the resistive layer. The disclosed enzyme layer can have hydrophilic properties with water absorption of more than 10% by dry weight, as well as fast water absorption and rapid stabilization, so that sensor start-up is not negatively affected.

[0202] The enzyme layer disclosed herein may include an enzyme layer polymer. The enzyme layer polymer may be a polyzwitterion. A polyzwitterion is a polymer in which the repeat units of the polymer chain are zwitterionic moieties. As such, these polymers have equal numbers of cationic and anionic groups due to each zwitterionic repeat unit having both positive and negative charges, and therefore often have an overall zero charge throughout a wide pH range. Without being bound by theory, it is believed that the zwitterionic groups in the enzyme layer polymer provide charge centers for strong charge-charge interactions with the ionic groups in the enzyme, which may aid in immobilizing the enzyme in the enzyme layer and reducing leakage of the enzyme from the enzyme layer (and sometimes into the host). Additionally, the zwitterionic groups are highly hydrophilic and retain water, helping to prevent denaturation of the enzyme.

[0203] The enzyme layer polymers are polyzwitterionic, which is distinguished from other polyampholytes in that polyampholytes contain anionic and cationic groups, but the ionic groups are not correlated with each other as part of the same repeating unit. Thus, the anionic and cationic groups may be randomly spaced apart from each other, or there may be more of one ionic group than the other. Thus, it is typical for polyampholytes to have a net charge, except perhaps over a somewhat narrow pH range.

[0204] The disclosed polyzwitterions can have a variety of repeat units exemplified as i) to vii) below, where n is an integer between 2 and 1000.

[0205] [ka]

[0206] In structures i-iv), the zwitterionic units are attached to the backbone (~~~~) and the charges are on side groups suspended from the chain. In structures v)-vii), the zwitterionic units are such that one or both charges are on the chain itself.

[0207] Examples of suitable zwitterionic monomers that can be used to generate polyzwitterions of any of structures i)-vii) include: Included are ammoniophosphates (phosphobetaines or lecithin analogs), ammoniophosphonates (phosphonobetaines), or ammoniophosphinates (phosphinobetaines), each having the structure:

[0208] [ka]

[0209] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 , R 3 , and R 4 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R 3 , R 4 and one or more of Z are substituted with a polymerizable group.

[0210] Further examples of suitable zwitterionic monomers that can be used to generate polyzwitterions of any of structures i)-vii) include ammoniosulfonates (sulfobetaines), ammoniosulfates, each having the following structure:

[0211] [ka]

[0212] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 and R 3 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R 3 and one or more of Z are substituted with a polymerizable group; Ammoniocarboxylates have the structure:

[0213] [ka]

[0214] wherein Z is a branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 2 and R 3 is independently selected from alkyl, heteroalkyl, cycloalkyl, heterocycloalkyl, aryl, or heteroaryl; R 1 , R 2 , R 3 and one or more of Z are substituted with a polymerizable group.

[0215] In each of these monomers, Z can have a length of 1 to 12 atoms, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 atoms, and any of these values ​​can form the upper or lower endpoints of a range.

[0216] These monomers can be prepared by methods known to those of skill in the art, for example, as detailed in Laschewsky, “Structures and synthesis of zwitterionic polymers,” Polymers 6:1544-1601, 2014. In certain examples, the disclosed polyzwitterions can have repeating zwitterionic units derived from any of the zwitterionic monomers disclosed above.

[0217] The enzyme layer polymer may also include polyurethane and / or polyurea segments. For example, the enzyme layer polymer may include polyurethane copolymers such as polyether-urethane-urea, polycarbonate-urethane, polyether-urethane, silicone-polyether-urethane, silicone-polycarbonate-urethane, polyester-urethane, polyurethane-urea, etc. These polyurethane and / or polyurea segments are referred to herein as "hard segments" because they contain urea and / or urethane linkages formed from polyisocyanates and short chain polyols or polyamines, moieties that are rich in hydrogen bonds. These segments may also be relatively hydrophobic.

[0218] In addition to the polyurethane and / or polyurea hard segments, the disclosed enzyme layer polymers may also contain soft segments that have relatively poor hydrogen bonding. The soft segments are typically composed of polyols such as polycarbonates, polyesters, polyethers, polyarylenes, and polyalkylenes. The soft segments can be either hydrophobic or hydrophilic.

[0219] The enzyme layer polymers useful in certain embodiments may comprise linear or branched polymers on the backbone structure of the polymer. Thus, either the hard or soft segments may comprise a branched or linear backbone.

[0220] Zwitterionic monomers, as described herein, can be part of either the hard or soft segments, or both.

[0221] In some embodiments, the hard segment portion of the enzyme layer polymer may comprise about 5% to about 50% by weight of the polymer, sometimes about 15% to 20% by weight, and other times about 25% to 40% by weight. The hard segment may have a molecular weight of about 160 daltons to about 10,000 daltons, and sometimes about 200 daltons to about 2,000 daltons. In some embodiments, the molecular weight of the soft segment may be about 200 daltons to about 10,000,000 daltons, sometimes about 500 daltons to about 5,000 daltons, and sometimes about 500 daltons to about 2,000 daltons.

[0222] As stated, the hard segment can be a polyurethane or a polyurea. Polyurethanes are polymers produced by the condensation reaction of diisocyanates and difunctional hydroxyl-containing materials. Polyureas are polymers produced by the condensation reaction of diisocyanates and difunctional amine-containing materials. Preferred diisocyanates include aliphatic diisocyanates containing from about 4 to about 9 methylene units. Cycloaliphatic moieties containing diisocyanates can also be useful in preparing the polymer and copolymer components of the membranes of the preferred embodiments.

[0223] The soft segments used in preparing the enzyme layer polymer may be polyfunctional aliphatic polyols, polyfunctional aliphatic or aromatic amines, etc., which may be useful in effecting permeability of the analyte (e.g., glucose) therethrough, and may include, for example, polyoxazolines, poly(ethylene glycol)s (PEGs), polyacrylamides, polyimines, polypropylene oxides (PPOs), PEG-co-PPO diols, silicone-co-PEG diols, silicone-co-PPO diols, polyethyl acrylates (PEAs), polyvinylpyrrolidones (PVPs), and modifications thereof (e.g., PVP vinyl acetate), where PEGs and modifications thereof may be preferred due to their hydrophilicity.

[0224] In some embodiments, the soft segment portion of the enzyme layer polymer may comprise about 5% to about 70% by weight of the polymer, sometimes about 15% to 20% by weight, and other times about 25% to 40% by weight. The soft segment may have a molecular weight of about 160 daltons to about 10,000 daltons, and sometimes about 200 daltons to about 2,000 daltons. In some embodiments, the molecular weight of the soft segment may be about 200 daltons to about 10,000,000 daltons, sometimes about 500 daltons to about 5,000 daltons, and sometimes about 500 daltons to about 2,000 daltons.

[0225] In some embodiments, the enzyme layer polymer comprising hard and soft segments, and zwitterionic repeat units, can have a molecular weight of from about 10 kDa to about 500,000 kDa, e.g., from about 10 kDa to about 100,000 kDa, from about 1000 kDa to about 500,000 kDa, from about 10,000 kDa to about 100,000 kDa, and from about 100,000 kDa to about 500,000 kDa.

[0226] The hard and soft segments may each be selected for their properties, such as, but not limited to, tensile strength, flex life, modulus, etc. For example, polyurethanes are relatively strong and offer many reaction pathways, properties that may be advantageous for the membrane domain of a continuous sensor.

[0227] As stated, the enzyme layer polymers contain one or more zwitterionic repeat units, and thus these groups are "internal" with respect to the polymer backbone. Such "internal" repeat units are distinct from materials found at the ends of polymer chains, since such moieties are only attached to the polymer chain at one position. The disclosed enzyme layer polymers may, in some embodiments, have one or more zwitterionic groups at the ends of the polymer chain, but such groups are not the only zwitterionic groups in the chain, and there is at least one internal zwitterionic group in the backbone.

[0228] In some embodiments, the enzyme layer polymer comprises at least about 1%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30% to about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, or about 55% by weight of zwitterionic repeat units. In a preferred embodiment, the enzyme layer polymer comprises at least about 20% zwitterionic repeat units by weight of the polymer.

[0229] The zwitterionic repeat units may be betaines, precursors or derivatives thereof (e.g., alkyl betaines or amino betaines), such as carboxyl, sulfo, or phospho betaine compounds. These segments or moieties may be incorporated into the enzyme layer polymer, whether in the hard segments, soft segments, or both, for example, up to about 55% by weight of the enzyme layer polymer.

[0230] In some embodiments, two or more different zwitterions or zwitterion precursor segments or moieties are used, while in other embodiments, a single zwitterion or zwitterion precursor segment or moiety may be used in the enzyme layer polymer.

[0231] Some examples of enzyme layer polymers are illustrated diagrammatically in FIG. 12. In general, enzyme layer polymers include one or more hard segments and one or more soft segments. The hard segments can be aliphatic or aromatic monomers. The soft segments can be hydrophilic or hydrophobic oligomers, such as polyalkylene glycols, polycarbonates, polyesters, polyethers, polyvinyl alcohols, polyvinylpyrrolidones, polyoxazolines, and the like. Zwitterionic groups (e.g., betaines) can be part of the soft segment, the hard segment, or both. As illustrated in FIG. 12, a variety of hard and soft segments can be present, which allows for tuning of the properties of the enzyme layer polymer by using different segments, different segment lengths, functionalization of certain segments, crosslinking of certain segments, and the like. In some embodiments, biocompatible segmented block polyurethane copolymers including hard and soft segments can be used in the enzyme layer.

[0232] Incorporation of these zwitterionic repeat units into a polymer can be accomplished by using zwitterionic monomers that have a diol or diamine (e.g., at the Z position) or R 1 ~R 4 The diol or diamine may be attached at any of R 1 ~R 4 Attachment to a diol or diamine in can be achieved by reacting the corresponding precursor with a halo-substituted diamine or diol. Examples of such monomers are shown below:

[0233] [ka]

[0234] wherein W, Y, and Z are independently branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl, any of which may be optionally substituted with O, OH, halogen, amino, or alkoxyl; R1 is H, alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 2 , R 3 , and R 4 is independently selected from alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl. In certain examples, W is C1-C4 alkyl. In certain examples, Y is C1-C4 alkyl. In other examples, Z is C1-C4 alkyl.

[0235] These compounds can be reacted with diisocyanates to form polyurethanes or polyureas. Alternatively, the carboxylate, sulfonate, phosphinate, or phosphonate moieties can be protected and then the protecting groups removed after polymerization. In another alternative, the amines can be tertiary amines and then quaternized by alkylation after polymerization.

[0236] Another method involves the radical polymerization of zwitterionic monomers having unsaturation substituted at the Z position in the monomers shown above. In another example, zwitterionic monomers in which the unsaturation is attached to an ammonium group can be used in the radical polymerization. Examples of such monomers are shown below:

[0237] [ka]

[0238] In the formula, X is O, NH, or NR 4 Y and Z are independently branched or straight chain alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl, any of which may be optionally substituted with OH, halogen, or alkoxyl; R 1 is H, alkyl, heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl; R 3 and R 5is independently selected from heteroalkyl, cycloalkyl, cycloheteroalkyl, aryl, or heteroaryl. In certain examples, R 5 is H or CH3. In other examples, X is O. In yet other examples, X is NH or NCH3. In particular examples, Y is C1-C4 alkyl. In other examples, Z is C1-C4 alkyl.

[0239] Additional examples of suitable zwitterionic monomers include N-(2-methacryloyloxy)ethyl-N,N-dimethylammoniopropanesulfonate, N-(3-methacryloylimino)propyl-N,N-dimethylammoniopropanesulfonate, 2-(methacryloyloxy)ethylphosphatidylcholine, and 3-(2′-vinyl-pyridino)propanesulfonate.

[0240] In other embodiments, the enzyme layer polymers can be crosslinked. For example, polyurethaneurea polymers having aromatic or aliphatic segments with electrophilic functional groups (e.g., carbonyl, aldehyde, anhydride, ester, amide, isocyanate, epoxy, allyl, or halo groups) can be crosslinked with crosslinkers having multiple nucleophilic groups (e.g., hydroxyl, amine, urea, urethane, or thio groups). In further embodiments, polyurethaneurea polymers having aromatic or aliphatic segments with nucleophilic functional groups can be crosslinked with crosslinkers having multiple electrophilic groups. Still further, polyurethaneurea polymers having hydrophilic segments with nucleophilic or electrophilic functional groups can be crosslinked with crosslinkers having multiple electrophilic or nucleophilic groups. Unsaturated functional groups on the polyurethaneurea can also be used for crosslinking by reacting with multivalent free radical agents.

[0241] Non-limiting examples of suitable crosslinkers include isocyanates, carbodiimides, glutaraldehyde or other aldehydes, aziridines, silanes, epoxies, acrylates, free radical agents, ethylene glycol diglycidyl ether (EGDE), poly(ethylene glycol) diglycidyl ether (PEGDE), or dicumyl peroxide (DCP). In one embodiment, about 0.1 w / w% to about 15 w / w% of the crosslinker is added based on the total dry weight of the crosslinker, and the polymer is added when blending the components (in one example, about 1% to about 10%). During the curing process, substantially all of the crosslinker is believed to react, leaving substantially no detectable unreacted crosslinker in the final layer.

[0242] Furthermore, the disclosed enzyme layer may have zwitterions trapped or embedded in the polymer network by non-covalent interactions. Thus, in further embodiments, the disclosed enzyme layer may include an enzyme layer polymer and an additional betaine blended therewith. For example, the enzyme layer polymer may be blended with cocamidopropyl betaine, oleamidopropyl betaine, octyl sulfobetaine, caprylyl sulfobetaine, lauryl sulfobetaine, myristyl sulfobetaine, palmityl sulfobetaine, stearyl sulfobetaine, betaine (trimethylglycine), octyl betaine, phosphatidylcholine, glycine betaine, poly(carboxybetaine) (pCB), and poly(sulfobetaine) (pSB). It will be understood that many more zwitterionic compounds or precursors or derivatives thereof may be applicable, and that this list of exemplary betaines is not intended to limit the scope of the embodiments.

[0243] In certain embodiments, the enzyme layer may include a polyzwitterionic enzyme layer polymer and an enzyme. In other embodiments, the enzyme layer may include a polyzwitterionic enzyme layer polymer blended with a base polymer and an enzyme. Suitable base polymers may include, but are not limited to, silicone, epoxy, polyolefin, polystyrene, polyoxymethylene, polysiloxane, polyether, polyacrylic, polymethacrylic, polyester, polycarbonate, polyamide, poly(etherketone), poly(etherimide), polyurethane, and polyurethaneurea, where polyurethane and polyurethaneurea may include polyurethane copolymers such as polyether-urethane-urea, polycarbonate-urethane, polyether-urethane, silicone-polyether-urethane, silicone-polycarbonate-urethane, polyester-urethane, and the like. In some embodiments, the base polymers may be selected for their bulk properties, such as, but not limited to, tensile strength, flex life, modulus, and the like. For example, polyurethanes are known to be relatively strong and provide many reaction pathways, properties that may be advantageous as bulk properties for the membrane domain of a continuous sensor.

[0244] In some embodiments, a base polymer may be used that includes a biocompatible segmented block polyurethane copolymer that includes hard and soft segments. In some embodiments, the hard segment of the copolymer may have a molecular weight of about 160 Daltons to about 10,000 Daltons, and sometimes about 200 Daltons to about 2,000 Daltons. In some embodiments, the molecular weight of the soft segment may be about 200 Daltons to about 10,000,000 Daltons, and sometimes about 500 Daltons to about 5,000,000 Daltons, and sometimes about 500,000 Daltons to about 2,000,000 Daltons. It is contemplated that the polyisocyanate used for the preparation of the hard segment of the copolymer may be an aromatic or aliphatic diisocyanate. The soft segments used in preparing the polyurethanes may be polyfunctional aliphatic polyols, polyfunctional aliphatic or aromatic amines, and the like, which may be useful in effecting permeability of an analyte (e.g., glucose) therethrough, and may include, for example, polyvinyl acetate (PVA), poly(ethylene glycol) (PEG), polyacrylamide, acetate, polyethylene oxide (PEO), polyethyl acrylate (PEA), polyvinylpyrrolidone (PVP), poly(2-oxazoline (POX), and variants thereof (e.g., PVP vinyl acetate), where PVP, POX, and variants thereof may be preferred in some embodiments due to their hydrolytic stability.

[0245] In some embodiments, the one or more zwitterionic compounds or precursors thereof applied to the surface of the membrane system are hydrolyzable cationic esters of zwitterionic compounds. In these embodiments, the hydrolyzable cationic esters provide the added benefit that hydrolysis of the cationic ester to a non-fouling zwitterionic group may kill microorganisms (such as bacteria) or condense DNA. Furthermore, the mixed charge nature of the resulting zwitterionic group results in inhibition of non-specific protein adsorption on the surface of the sensor. In these embodiments, cationic betaine esters, such as cationic pCB esters, are preferred.

[0246] Incorporating zwitterion or zwitterion precursor segments or moieties into the polymer backbone can be difficult due to solubility issues associated with the zwitterion or zwitterion precursor monomers. Such groups can typically only be dissolved in highly polar solvents such as methanol and water, which are unfavorable for the synthesis of some enzyme layer polymers (e.g., polyurethanes). Thus, the available functional groups that can be chemically incorporated into and used in the backbone of the enzyme layer polymer by solution-based polycondensation synthesis are limited. As an alternative method of incorporating zwitterion or zwitterion precursor segments or moieties into the backbone of the base polymer, precursors or derivatives of the zwitterion or zwitterion precursor can be used. For example, zwitterion precursors and / or zwitterion derivatives with more desirable solubility characteristics in low polarity organic solvents can be used as monomers. Enzyme layer polymers (e.g., polyurethane ureas) can be synthesized by polycondensation reactions to form well-defined polymers with high molecular weights and low polydispersity indexes. These polymers can then be converted into zwitterionic group containing polymers via chemical reactions (hydrolysis, deprotection, thermally induced rearrangement, and UV induced degradation) or biologically induced reactions after in vivo implantation of the device.

[0247] In some embodiments, the enzymes contained in the enzyme layer are susceptible to heat or pH induced degradation. In some related embodiments, the enzyme layer may also include one or more enzyme stabilizers. Such agents improve the ability of the enzyme to withstand heat or pH induced denaturation. Thus, the inclusion of enzyme stabilizers facilitates device manufacturing by allowing the use of manufacturing processes that would otherwise reduce the activity of the enzyme. The inclusion of these agents has the added benefit of extending the usable shelf life of the sensor. Any material that improves the thermal and / or pH stability of the enzyme without affecting the oxygen permeability of the analyte or the enzyme layer until the enzyme layer is no longer suitable for use in the sensor may be used as an enzyme stabilizer. In some embodiments, the enzyme stabilizer may be bipolar. Without being bound by theory, it is believed that bipolar enzyme stabilizers stabilize the enzyme by orienting around the enzyme in such a way as to provide a charge local environment that stabilizes the tertiary structure of the enzyme.

[0248] Zwitterionic enzyme stabilizers can be zwitterionic or non-zwitterionic. That is, zwitterionic enzyme stabilizers are neutral molecules with positive and negative charges at different positions. In some embodiments, the positive and negative charges are full unit charges (i.e., the molecule is zwitterionic). In other embodiments, the positive and negative charges are less than full unit charges (i.e., the molecule is zwitterionic but non-zwitterionic).

[0249] In some embodiments, the zwitterionic enzyme stabilizer can be a betaine, such as glycine betaine, poly(carboxybetaine) (pCB), or poly(sulfobetaine) (pSB), or some other zwitterion, such as cocamidopropyl betaine, oleamidopropyl betaine, octyl sulfobetaine, caprylyl sulfobetaine, lauryl sulfobetaine, myristyl sulfobetaine, palmityl sulfobetaine, stearyl sulfobetaine, betaine (trimethylglycine), octyl betaine, phosphatidylcholine, ectoine, or hydroxyectoine. In a preferred embodiment, the zwitterionic enzyme stabilizer is glycine betaine. In some embodiments, the non-zwitterionic enzyme stabilizing reagent can be an amine oxide.

[0250] When used, the enzyme stabilizing reagent may be present at up to about 0.1, about 0.2, about 0.5, about 1, about 2, or about 5% by weight of the enzyme layer. It will be understood that many more zwitterionic groups, or precursors or derivatives thereof, may be applicable, and that this exemplary list of betaines is not intended to limit the scope of the embodiments. In some embodiments, hydrolyzable cationic esters of zwitterionic groups (discussed elsewhere) may be used at similar concentrations for incorporation into the enzyme layer.

[0251] In embodiments where the enzyme layer includes an enzyme stabilizing reagent, the amount of enzyme stabilizing reagent present in the enzyme domain is sufficient to provide improved thermal and / or pH stability of the enzyme, but does not interfere with the permeability characteristics of the enzyme layer, such that the sensor retains high glucose sensitivity. The identity and amount of enzyme stabilizing reagent used in the enzyme layer may vary based on the particular enzyme used in the sensor, but the amount of enzyme stabilizing reagent is generally less than about 50% by weight, such as less than about 25% by weight, such as less than about 10% by weight, of the amount of enzyme. In a preferred embodiment, the enzyme is glucose oxidase and the enzyme stabilizing reagent is a betaine, such as glycine betaine. In other embodiments, other enzymes (e.g., glucose dehydrogenase) and other stabilizers may be used.

[0252] In some embodiments, the enzyme and enzyme layer polymer, as well as any enzyme stabilizing agents, may be impregnated or otherwise immobilized in the biointerface layer or diffusion resistant domain, such that a separate enzyme layer is not required (e.g., now providing an integral domain that includes the functionality of the biointerface layer, the diffusion resistant domain, the interference domain, and the enzyme layer). In some embodiments, the enzyme layer is formed from an aqueous dispersion of polyurethane, e.g., a colloidal polyurethane polymer that includes the enzyme and the enzyme stabilizing reagent. Again, it is contemplated that in some embodiments, the polymer system of the enzyme layer may not be crosslinked, while in other embodiments crosslinking may be used and may be achieved by any of a variety of methods, e.g., by adding a crosslinking agent.

[0253] In some other embodiments, the blend of polymers containing two or more surface-active groups comprises one negatively charged surface-active group and one positively charged surface-active group. In some embodiments, the number of negatively and positively charged surface-active groups is such that the enzyme domain formed from the blend carries approximately a net neutral charge. In other embodiments, the number of positively and negatively charged surface-active groups may not be equal, and there are more of either the positively or negatively charged surface-active groups.

[0254] In some embodiments, a membrane is disclosed that includes an enzyme layer 44 (see Figures 2A-2C). The enzyme layer disclosed herein may include an enzyme layer polymer and an enzyme, or in alternative embodiments, the enzyme layer may include an enzyme layer polymer and one or more other polymers that form a polymer blend, and an enzyme.

[0255] In some embodiments, an enzyme layer 44 may be used, located closer to the electrochemical reaction surface than the diffusion resistance domain 46. The enzyme layer includes an enzyme configured to react with the analyte. In one embodiment, the membrane includes an immobilized enzyme layer 44 that includes glucose oxidase. In other embodiments, the enzyme layer 44 may be impregnated with other oxidases, such as galactose oxidase, cholesterol oxidase, amino acid oxidase, alcohol oxidase, lactate oxidase, or uricase. For example, for an enzyme-based electrochemical glucose sensor to work well, the sensor response should not be limited by enzyme activity or cofactor concentration.

[0256] In some embodiments, the enzyme can be impregnated or otherwise immobilized with the biointerface or diffusion resistance domain, such that a separate enzyme domain 44 is not required (e.g., where an integral domain is provided that includes the functionality of a biointerface domain, a diffusion resistance domain, and an enzyme domain). In some embodiments, the enzyme domain 44 is formed from a polyurethane, e.g., an aqueous dispersion of a colloidal polyurethane polymer that includes the enzyme.

[0257] In certain embodiments, the thickness of the enzyme layer can be about 0.01, about 0.05, about 0.1, about 0.5, about 1, about 2, about 4, about 6, about 8 μm to about 10, about 15, about 20, about 30, about 40, about 50, about 75, about 100, about 125, about 150, about 175, about 200, or about 250 μm. In some of these embodiments, the thickness of the enzyme layer can sometimes be about 1 to about 5 μm, and sometimes about 2 to about 7 μm. In other embodiments, the enzyme layer can be about 20 or about 25 μm to about 50, about 55, or about 60 μm thick. In some embodiments, the glucose sensor can be configured for transdermal or short-term subcutaneous implantation and can have a thickness of about 0.5 μm to about 8 μm, and sometimes about 4 μm to about 6 μm. In one glucose sensor configured for fluid communication with the host's circulatory system, the thickness can be from about 1.5 μm to about 25 μm, and sometimes from about 3 to about 15 μm. In some embodiments, the enzyme layer or any other layer of the electrode can have a consistent thickness, while in other embodiments, it is contemplated that the thickness can vary. For example, in some embodiments, the thickness of the enzyme layer can vary along the longitudinal axis of the electrode end. Interference Domain

[0258] In some embodiments, it is contemplated that an interference domain 43, also referred to as an interference layer, may be provided in addition to (or instead of) the biointerface layer, for example in the sensor configuration illustrated in FIG. 2B. The interference domain 43 may substantially reduce the permeation of one or more interferents to the electrochemical reaction surface. The interference domain 43 may be configured to be much less permeable to one or more of the interferents than the measured species. In some embodiments, where an interference barrier may be provided by the biointerface layer (e.g., via a surface-active group-containing polymer in the biointerface layer), there is no separate interference domain. In other embodiments, the membrane includes both an interference domain and a biointerface layer, and both domains are configured to reduce the permeation of one or more interferents. In further embodiments, the interference domain and the biointerface layer are each configured to reduce the permeation of a different interfering species. For example, the interference domain may have greater specificity than the biointerface layer for reducing the permeation of one type of interfering species, while the biointerface layer may have greater specificity than the interference domain for reducing the permeation of another type of interfering species. In some embodiments, both the interference domain and the biointerface layer are configured to target a particular interfering species for permeation reduction.

[0259] In certain embodiments, the implantable sensor employs a membrane system that includes a resistance domain, an enzyme domain, and an interference domain. The interference domain can be proximal to the sensor, and the resistance domain can be distal to the sensor, with the enzyme domain in between. The interference domain can consist of a single layer or multiple layers of the same material. However, in some embodiments, the interference domain includes layers of two or more different species in an alternating configuration. For example, a layer of a first type can be represented by X, a layer of a second type can be represented by Y, and a layer of a third type can be represented by Z. An interference domain including alternating layers can have the following exemplary configurations: XY YX XYX XYXYX XYXYXY XXYYXYXXYY XXXYYYXXXYYYXXX XYXYXYXYXYXYX XYZXYZXYZX XYXZXYXZXYXZ ZYYXZZZXYYYXZ

[0260] The above configurations, which are merely exemplary, illustrate various embodiments. In certain embodiments, the first and last layers are the same (e.g., X and X), while in other embodiments, the first and last layers are different (e.g., X and Y). A domain may include one or more layers and may be integral (i.e., a single layer is deposited, e.g., X) or composite (e.g., a first layer of material is deposited, followed by second and third, etc. layers of the same material deposited on the first layer, e.g., XXX). The pattern of alternating layers may be regular (e.g., XYXYXYXYXY) or irregular (e.g., ZYXZXYZYZ).

[0261] In some embodiments, the alternating layers include polyanion layers and polycation layers. The following are exemplary interference domain configurations, where the polyanion layers (unitary, multiple, and / or consecutive with the same or different polyanions) are represented by A, and the polycation layers (unitary, multiple, and / or consecutive with the same or different polyanions) are represented by C: CA CAC CACA CACAC CACACA CACACAC CACACACA CACACACAC CACACACACA CACACACACAC CACACACACA CACACACACACAC CACACACACACA CACACACACACACAC CAKECAKECAKECAKE CRAP CRAP CRAP CRAP CACACACACACACACACACA CACACACACACACACACACA CRAP CRAP CRAP CRAP CRAP CACACACACACACACACACACACA CRAP CRAP CRAP CRAP CRAP CRAP CACACACACACACACACACACACA CACACACACACACACACACACACACACA CACACACACACACACACACACACACACA CACACACACACACACACACACACACACACA CACACACACACACACACACACACACACACACA CACACACACACACACACACACACACACACACACA CACACACACACACACACACACACACACACACACACACA NEEDLE ACA acacia acacia ACACAC ACACACA ACACACAC ACAC ACACACACAC ACAC ACACACACACAC ACACACACACACA ACACACACACACACA ACAC ACACACACACACACACA ACAC ACACACACACACACACAC ACACACACACACACACACACA ACACACACACACACACACACACA ACAC ACACACACACACACACACACAC ACACACACACACACACACACACAC ACACACACACACACACACACACAC ACACACACACACACACACACACACAC ACACACACACACACACACACACACACACAC ACACACACACACACACACACACACACACACAC ACACACACACACACACACACACACACACA ACACACACACACACACACACACACACACACACA

[0262] Other configurations (e.g., those including additional layers and / or additional materials) are also contemplated for some embodiments. In some embodiments, each A layer is a monolithic or composite layer of the same polyanion, and each C layer is a monolithic or composite layer of the same polycation. Both of the outermost layers of the interference domain may be polycation layers, with the polyanion layer being present only as an internal layer. Any suitable number of alternate layers may be used in the interference domain, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or more bilayers (defined as a polycation layer adjacent to a polyanion layer). In some embodiments, a final polycation layer is added to provide an interference domain with a polycation layer as the outermost layer. In other embodiments, a final anion layer is added to provide an interference domain with a polyanion layer as the outermost layer.

[0263] Polyanions and polycations belong to a class of polymers commonly referred to as polyelectrolyte-polymers, where at least some of the repeating units (or monomers) contain one or more ionic moieties. Polyelectrolytes that carry both cationic and anionic moieties are commonly referred to as polyampholytes. Certain polyelectrolytes form self-assembled monolayers, where one end of the molecule exhibits a specific reversible affinity for a substrate, whereby an organized close-packed monolayer of polyelectrolytes can be deposited.

[0264] The polycation can be any biocompatible polycationic polymer. In some embodiments, the polycation is a biocompatible water-soluble polycationic polymer. In certain embodiments, water solubility can be enhanced by grafting the polycationic polymer with a water-soluble polynonionic material such as polyethylene glycol. Representative polycationic materials can include, for example, natural and non-natural polyamino acids, positively charged polysaccharides, and positively charged synthetic polymers that have a net positive charge at neutral pH. Additional examples of suitable polycationic materials include polyamines having amine groups either in the polymer backbone or in the polymer side chains, such as poly-L-lysine and other positively charged polyamino acids of natural or synthetic amino acids or mixtures of amino acids, including poly(D-lysine), poly(ornithine), poly(arginine), and poly(histidine), as well as non-peptide polyamines, such as poly(aminostyrene), poly(aminoacrylate), poly(N-methylaminoacrylate), poly(N-ethylaminoacrylate), poly(N,N-dimethylaminoacrylate), poly(N,N-diethylaminoacrylate), poly(diallyldimethylammonium chloride), poly(amino methacrylate), poly(N-methylamino- ... Poly(N-ethylamino methacrylate), poly(N,N-dimethylamino methacrylate), poly(N,N-diethylamino methacrylate), poly(ethyleneimine), polymers of quaternary amines such as poly(N,N,N-trimethylamino acrylate chloride), poly(methylacrylamidopropyl trimethylammonium chloride), and natural or synthetic polysaccharides such as chitosan, poly(allylamine hydrochloride), poly(diallyldimethylammonium chloride), poly(vinylbenzyltrimethylamine), polyaniline or polyaniline sulfonate, (p-doped), polypyrrole (p-doped), polyallylamine gluconolactone, and poly(pyridinium acetylene).

[0265] The polyanionic material can be any biocompatible polyanionic polymer, for example, any polymer with carboxylic acid groups attached as pendant groups. The polyionic layer can be hydrophilic (e.g., a material or portion thereof that will more readily associate with water than with lipids). In some embodiments, the polyanionic polymer is a biocompatible water-soluble polyanionic polymer. Suitable materials include, but are not limited to, alginate, carrageenan, furcellaran, pectin, xanthan, hyaluronic acid, heparin, heparan sulfate, chondroitin sulfate, dermatan sulfate, dextran sulfate, polymethacrylic acid, polyacrylic acid, poly(vinyl sulfate), poly(thiophene-3-acetic acid), poly(4-styrenesulfonate), poly(styrenesulfonate), (Poly[1-[4-(3-carboxy-4-hydroxy-phenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]), poly(4-[4-({4-[3-amino-2-(4-hydroxy-phenyl)propylcarbamoyl]-5-oxo-pentyl-}-methyl-amino)-phenylazo]-benzenesulfonic acid), oxidized cellulose, carboxymethylcellulose, and crosmarmelose, synthetic polymers, and copolymers containing pendant carboxyl groups, such as those containing maleic or fumaric acid in the backbone. Predominantly negatively charged polyamino acids are also suitable. Examples of these materials include polyaspartic acid, polyglutamic acid, and their copolymers with other natural and unnatural amino acids. Polyphenolic materials such as tannins and lignins may be used if they are sufficiently biocompatible.

[0266] The molecular weight of the polyionic material can be varied to change coating characteristics such as coating thickness. As the molecular weight is increased, the coating thickness generally increases. However, increasing the molecular weight can make handling more difficult. To achieve a balance between coating thickness, material handling, and other design considerations, the polyionic material can have a specific average molecular weight Mn. In some embodiments, the average molecular weight of the polyionic material used is about 1,000, 10,000, or 20,000 to about 25,000, 50,000, 100,000, or 150,000 g / mol.

[0267] In some embodiments, interference domains can be prepared using a layer-by-layer method, in which a substrate (e.g., a sensor or a membrane layer on a sensor, such as a resistive layer or an enzyme layer) is first immersed in one polyelectrolyte bath and then in a bath of an oppositely charged polyelectrolyte. Optionally, the substrate can be immersed in a wash bath before or after it is immersed in the polyelectrolyte bath. During each immersion, a small amount of polyelectrolyte is adsorbed and the surface charge is reversed, thereby allowing for a stepwise and controlled construction of an electrostatically crosslinked (or hydrogen-bonded) film of alternating polycation-polyanion layers. This method provides a technique for controlling functionality, as well as film thickness and functionality. For example, it can be used to deposit films as thin as one monolayer, or for thicker layers. Figure 11B illustrates one embodiment of the layer-by-layer method, which uses the alternating adsorption of polycations and polyanions to create the structure shown in Figure 11A. Operationally, the embodiment illustrated in FIG. 11B occurs through sequential exposure of substrate 938 to polycation and polyanion solutions, washing to remove unadsorbed polymer after each deposition step. In a first step, polycation 942 is deposited on substrate 938 (e.g., a wire or flat wafer substrate with an electroactive surface) to form polycation layer 942. As described in more detail elsewhere herein, deposition of the layer may be performed using any of a variety of techniques, such as, for example, dipping and / or spraying. In a second step, deposition of polycation layer 942 is followed by washing to remove unadsorbed polymer. Then, in a third step, polyanion 944 is deposited on polycation layer 942. Then, in a fourth step, deposition of polyanion layer 944 is followed by washing to remove unadsorbed polymer. These steps can be repeated until the desired interference domain configuration and / or structure is achieved. In an alternative embodiment, instead of depositing a polycation layer on substrate 938 as the first layer, a polyanion layer is deposited instead. A second layer formed of a polycation is then deposited on top of the first, i.e., polyanion layer. This process is continued until a particular desired interference domain configuration and / or structure is achieved.

[0268] In some embodiments, the method may also use other interactions such as hydrogen bonds or covalent bonds. Depending on the nature of the polyelectrolyte, polyelectrolyte cross-linking may occur, where a single polyelectrolyte chain adsorbs to two (or more) oppositely charged macroions, thereby establishing molecular bridges. If only a monolayer of each polyelectrolyte is adsorbed at each deposition step, electrostatically cross-linked hydrogel-type materials can be built up on the surface a few microns at a time. If the substrate is not thoroughly washed between applications of the polyion films, thicker hydrogel-like structures may be deposited.

[0269] In some embodiments, the interference-blocking ability provided by the alternating polycation layer(s) and polyanion layer(s) can be adjusted and / or controlled by creating covalent bonds between the polycation layer(s) and the polyanion layer(s). Crosslinking can have a substantial effect on the mechanical properties and structure of the film, which in turn can affect the interference-blocking ability of the film. Crosslinked polymers can have different crosslinking densities. In certain embodiments, crosslinking is used to promote crosslinking between layers. In other embodiments, instead of (or in addition to) the crosslinking techniques described above, heat is used to form crosslinks. For example, in some embodiments, imide and amide bonds can be formed between the polycation layer and the polyanion layer as a result of high temperature. In some embodiments, photocrosslinking is performed to form covalent bonds between the polycation layer(s) and the polyanion layer(s). One major advantage over photocrosslinking is that it offers the possibility of patterning. In certain embodiments, patterning using photocrosslinking is performed to modify the film structure and thus tune the interference-blocking ability of the interference domains. The blocking ability may correspond to, but is not limited to, the ability to reduce the transport of certain interfering species, or the selectivity of the transport of a desired species (e.g., H2O2) over an interfering species. Post-deposition reactions, such as cross-linking and reduction of metal ions to form nanoparticles, provide additional methods for modifying film properties. In some embodiments, cross-linking can be performed during the deposition of adjacent polycation or polyanion layers instead of (or in addition to) a post-deposition cross-linking process.

[0270] The total thickness of the interference layer may affect its permeability to interferents. The total thickness of the interference domain may be controlled by adjusting the number of layers and / or the degree of washing between layers. By layer deposition by spraying, control of droplet size and density may provide a coating of a desired selected thickness without necessarily requiring washing between layers. Furthermore, excess (unbound) material may be removed via other means, for example by air jets. If residual polyelectrolytes from the previous layer are substantially removed before adding the subsequent layer, the thickness per layer is reduced. Thus, in one embodiment, the surface is first coated with polycations, then excess polycations are removed by washing the surface, after which polyanions are added, then excess is removed, and the process is repeated as necessary. In some embodiments, polycations or polyanions from different adjacent layers may be intertwined. In further embodiments, they may be intertwined over several layers.

[0271] In some embodiments, the level of ionization of the polyions can be controlled, for example, by controlling the pH in the immersion solution containing the polycations or polyanions. By changing the level of ionization of these polyions, the interference blocking ability of a certain layer may be changed and / or controlled. For example, a first polycation layer with a higher level of ionization than a second polycation layer may interact better with a first interfering species and reduce its transport, while the second polycation layer may interact better with a second interfering species and reduce its transport. Changes in the level of ionization of the charge groups of the polyions can also affect the mechanical, structural, and certain other properties (e.g., diffusion properties) that can affect the ability of the interference domain to reduce (or totally block) the transport of the interfering species. For example, an alternating bilayer containing a polycation and a polyanion, both with a high level of ionization, may bind more tightly than a corresponding bilayer with a low level of ionization. Thus, structural differences between these two membranes, which may be in the form of mechanical or other properties (e.g., thickness of the domain), can affect the performance of the interference domain.

[0272] In some embodiments, the linear charge density of the polyelectrolyte can be controlled at least in part by the average charge spacing along the polyion chain. The spacing between the charge groups on the polycationic and / or polyanionic polymers that form the interference domain can be controlled by polyelectrolyte polymer selection or polymer synthesis. How far apart the charge groups are spaced can greatly affect the structural properties of the interference domain. For example, polyions with charge groups spaced close to each other can result in small pores in the interference domain, thereby resulting in a structure that excludes the passage of medium and large interfering species through it, but allows the passage of small pores through it. Conversely, polyions with charge groups spaced at a moderate distance from each other can result in medium pores that exclude large interfering species and allow the passage of medium and small interfering species through it. In certain embodiments, the linear charge density of the polyanionic polymer is about 1-50 e / Å, sometimes about 10-25 e / Å, sometimes about 2-10 e / Å, and sometimes 2-3 e / Å, where e is the elementary charge of an electron / proton and Å is the distance in angstroms. In some embodiments, the linear charge density of the polycationic polymer is about 1-50 e / Å, sometimes about 10-15 e / Å, sometimes about 2-10 e / Å, and sometimes 2-3 e / Å.

[0273] In some embodiments, the linear charge density of the polyanion polymer is substantially similar to the linear charge density of the polycation polymer. For example, in one embodiment, the polyanion layer is formed of (i) poly(acrylic acid) having an average linear charge density of about 2.5 e / Å, and (ii) poly(allylamine hydrochloride), also having an average linear charge density of about 2.5 e / Å. In certain embodiments, the polycation layer and the polyanion layer can have average linear charge densities substantially equal to each other, between about 1-50 e / Å, sometimes between about 2-25 e / Å, sometimes between about 5-10 e / Å, other times between about 10-15 e / Å, and other times between about 15-25 e / Å.

[0274] By providing interference domains with different linear charge densities, interference domains can be formed that contain different polycation / polyanion bilayers specifically designed to exclude different interfering species based on certain characteristics (e.g., molecular diameter) of the targeted interfering species. For example, in one embodiment, the outermost bilayer of the interference domain is designed to have an intermediate average charge spacing, resulting in a bilayer that excludes only large molecular diameter species but allows the passage of medium and small molecular diameter species therethrough. Conversely, the innermost bilayer of the interference domain may be designed to have a low average charge spacing, resulting in a bilayer that excludes all molecules except those with very small molecular diameters, e.g., H2O2.

[0275] In some embodiments, the polycation layers may be formed of the same or substantially the same material (e.g., poly(allylamine hydrochloride) (PAH) in the case of polycations, or poly(acrylic acid) (PAA) in the case of polyanions), but have different levels of ionization. For example, in one embodiment, the interference domain comprises seven alternating polyelectrolyte layers, the first, third, fifth, and seventh layers being polycation layers and the second, fourth, and sixth layers being polyanion layers, where the first and seventh layers form the outer layers of the interference domain. In one embodiment, each or some of the polycation layers may have different levels of ionization. For example, in one embodiment, the first, third, fifth, and seventh layers may each have different levels of ionization, with the first layer having the highest level of ionization and the seventh layer having the lowest level of ionization, or vice versa. In alternative embodiments, some of the polycation layers may share substantially the same level of ionization. For example, in one embodiment, the first and seventh layers may have substantially the same level of ionization, while the third and fifth layers may have a different level of ionization than the others. As described elsewhere herein, the ionization level of the polyions may be controlled by controlling the pH in the immersion solution containing the polycations or polyanions. By varying the level of ionization of these polyions, the interference blocking ability of a particular layer may be altered and / or controlled.

[0276] The design of interference domains with layers having levels of ionization can be applied to polyanion layers as well. For example, in one embodiment with seven alternating polyelectrolyte layers, the second, fourth, and sixth layers can each be polyanion layers and each have a different level of ionization, with the second layer having the highest level of ionization and the sixth layer having the lowest level of ionization, or vice versa. In alternative embodiments, some of the polyanion layers can share substantially the same level of ionization. For example, in one embodiment, the second and fourth layers can have substantially the same level of ionization, while the sixth layer can have a substantially different level of ionization from the others.

[0277] In certain embodiments, the particular polycation layer(s) and / or polyanion layer(s) selected to form the interference layer may depend at least in part on their ability to block, reduce, or impede the passage of one or more interferents therethrough. For example, a polyanion layer may be selected for its ability to block, reduce, or impede the passage of a first interferent, while a polycation layer may be selected for its ability to block, reduce, or impede the passage of a second interferent. A layer may be designed to slow down but not block the passage of interferents therethrough, or may be designed to substantially block (e.g., capture) the interferent therein. Additional polyion layers may be included in interference domains that still have specific selectivity for different interferents. Depending on the location of the interference domain in the membrane system relative to the electrode or electroactive surface of the sensor, the permeability of the layer to substances other than the interferents may be important. In a sensor system in which H2O2 (hydrogen peroxide) is produced by an enzyme-catalyzed reaction of the analyte to be detected, the interference domain should be designed to allow H2O2 to pass with minimal impedance when it is positioned between the electroactive surface and the enzyme layer. On the other hand, in a different membrane design, when the interference domain is positioned distal to the enzyme layer (with respect to the electroactive surface), in some embodiments, the interference domain can be designed to block H2O2 not produced by the enzyme-catalyzed reaction from passing through it. Furthermore, with this particular membrane design, the interference domain can be configured to allow the analyte and oxygen to pass with minimal impedance.

[0278] The application of layers in forming interference domains can be accomplished by various methods known in the art. One coating process embodiment simply involves dip-coating and dip-washing steps. Another coating process embodiment simply involves spray-coating and spray-washing steps. However, many alternative embodiments involve various uses of combinations of spray-coating, dip-coating, and / or washing steps. For example, one dip-coating method involves applying a coating of a first polyionic material to a substrate (e.g., a sensor or a membrane layer on a sensor, e.g., a resistance layer or an enzyme layer) by immersing the substrate in a first solution of the first polyionic material), washing the substrate by immersing the substrate in a washing solution, and optionally drying the substrate. This procedure is then repeated using a second polyionic material, the second polyionic material having an opposite charge to that of the first polyionic material, to form a polyionic bilayer. This bilayer formation process can be repeated multiple times to generate interference domains. In some embodiments, the number of bilayers can be from 1 to about 16 bilayers, sometimes from 1 to about 10 bilayers, and sometimes from about 3 to about 7 bilayers. In certain embodiments, a final layer of oppositely charged polyionic material can be deposited, whereby the first and final layers have the same charge (both positive or both negative). The immersion time for each of the coating and washing steps can vary depending on many factors. For example, immersion of the substrate in the polyionic solution can occur for a period of about 1 to 30 minutes, or about 2 to 20 minutes, or about 1 to 5 minutes. Washing can be accomplished in one step, although multiple washing steps can also be used. A series of about 2 to 5 washing steps can be used, with each immersion in the washing solution taking, for example, about 1 to about 3 minutes. In some embodiments, several polycation solutions and / or several polyanion solutions can be used.For example, in certain embodiments, a dip-coating sequence may entail applying a coating of a first polycationic material to a substrate to form a first layer, then applying a first anionic material to the first layer to form a second layer, then applying a second polycationic material to the second layer to form a third layer, then applying a second polyanionic material to form a fourth layer, then applying either the first or second polycationic material to the fourth layer to form a fifth layer. In some of these embodiments, the dip-coating sequence may be interspersed with washing steps performed between coating steps. Any of a variety of permutations involving the steps and materials described may be used. In alternative embodiments, the materials used to form the polycationic and / or polyanionic layers may be substantially the same. However, an individual polycationic layer may have a different level of ionization than one or more other polycationic layers in interference domains, and an individual polyanionic layer may also have a different level of ionization than one or more other polyanionic layers. For example, in one embodiment, the dip-coating sequence method involves the use of a first solution at a first pH containing a polycationic material, a second solution at a second pH containing a polyanionic material, a third solution at a third pH containing said polycationic material, a fourth solution at a fourth pH containing said polyanionic material, and a fifth solution at a fifth pH containing said polycationic material. Even if the same polycationic material is used to form the first, third, and fifth layers, the ionization levels of the first, third, and fifth layers will be different because the solutions used to form the first, third, and fifth layers have different pHs. Similarly, even if the same polyanionic material is used to form the second and fourth layers, the ionization levels of the second and fourth layers will be different because the solutions used to form the second and fifth layers have different pHs. This difference in ionization levels can affect, among other things, the mechanical properties of the film, the structural properties of the film (e.g., porosity, roughness), the diffusion properties of the film, and the selectivity of a particular polyelectrolyte layer for one particular interfering species over another.All of these effects affect the ability of each polyelectrolyte layer and interference domain to reduce the transport of various interfering species. In certain embodiments, at least two polycation layers and / or two polyanion layers of an interference domain are formed from the same polycationic / polyanionic material, but using solutions at different pH. In some of these embodiments, the first polycation layer has a higher selectivity for a particular interfering species than other interfering species, while the second polycation layer has a higher selectivity for a different interfering species than other interfering species.

[0279] Alternatively, or in addition, spray coating techniques may be used. In one embodiment, the coating process generally includes applying a coating of a first polyionic material to a substrate by contacting the substrate with a first solution of the first polyionic material, washing the substrate by spraying the substrate with a washing solution, and (optionally) drying the substrate. Similar to the dip coating process, the spray coating process can then be repeated with a second polyionic material, the second polyionic material having an opposite charge to that of the first polyionic material. Contact of the substrate with either the polyionic material or the washing solution can occur by various methods. For example, the substrate may be immersed in both solutions. One alternative is to apply the solution in a spray or mist form. Of course, various combinations are possible and within the scope of the contemplated embodiments, for example, spraying the substrate with a washing solution after immersing it in the polyionic material. Spray coating application can be achieved through a number of methods known in the art. For example, a conventional spray coating arrangement may be used, i.e., the liquid material is sprayed by applying the fluid through a small diameter nozzle, which may or may not be at elevated or reduced pressure, directed towards a deposition target. Another spray coating technique involves the use of ultrasonic energy, whereby the liquid is atomized by ultrasonic vibrations of a spray-forming tip, thereby turning it into a spray.

[0280] Yet another technique involves electrostatic spray coating, where an electric charge is carried into the fluid or droplets, increasing the efficiency of the coating. Further methods of atomizing liquids for spray coating require pure mechanical energy, for example, by contacting the liquid with a high-speed reciprocating member or a high-speed rotating disk. Yet another method of generating microdroplets for spray coating involves the use of piezoelectric elements to atomize the liquid. These techniques can be used with air assist or with elevated solution pressure. Furthermore, a combination of two or more techniques can prove more useful in certain materials and conditions. A method of spray application involves dispensing a polyanion or polycation solution into an ultrasonic dispensing head using a metering pump. The polyion layer is sprayed to allow the surface droplets to coalesce across the material surface. The resulting layer can then be allowed to interact for a period of time or can be immediately washed with water or saline solution (or other solutions that do not contain polyanions or polycations).

[0281] In some embodiments, the layers of the interference domain may include a polymer having a conjugated π system. The polymer having a conjugated π system may contain a delocalized electron system and may be conductive. The layers of the polymer having a conjugated π system may interact with each other through intermolecular forces, such as electrostatic π-π interactions (i.e., π-stacking). The conjugated polymer may provide beneficial properties of the interference domain, such as increasing the rigidity, integrity, and / or reproducibility of the domain. In some embodiments, the polymer having a conjugated π system may be polyacetylene, polypyrrole, polythiophene, poly(p-phenylene), poly(p-phenylenevinylene), or poly(carbazole). The interference domain may include alternating layers of any of the conjugated polymers described above. In some embodiments, the number of layers of the conjugated polymer may be from 1 to about 20 layers, sometimes from about 3 to about 10 layers.

[0282] In some embodiments, the thickness of the interference domain can be from about 0.01 microns or less to about 20 microns or more. In some of these embodiments, the thickness of the interference domain can be from about 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 1, 1.5, 2, 2.5, 3, or 3.5 microns to about 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 19.5 microns. In some of these embodiments, the thickness of the interference domain can be from about 0.2, 0.4, 0.5, or 0.6 microns to about 0.8, 0.9, 1, 1.5, 2, 3, or 4 microns. Polyimine Film

[0283] In some embodiments, certain polymer films can be used to form interference domains. For example, certain polyimides prepared from 2,2′-dimethyl-4,4′-diaminobiphenyl and the corresponding dianhydrides can be cast into films that can be used as hydrogen peroxide selective membranes. See, for example, Ekinci et al., Turk. J. Chem. 30 (2006), 277-285. In one embodiment, the films are prepared using the following steps: First, n-methyl-2-pyrrolidone (NMP) is distilled under reduced pressure onto CaH2 and stored over about 4 Å molecular sieves. Reagent grade pyromellitic dianhydride (PMDA) is sublimated under reduced pressure at about 250° C. and dried under vacuum at about 120° C. before use. The diamine is purified via recrystallization from ethanol to obtain shiny crystals. Next, 2,20-dimethyl-4,40-diaminobiphenyl (about 1.06 g, about 5 mmol) is dissolved in NMP (about 15 mL) in a 50 mL Schlenk tube equipped with a nitrogen line, an overhead stirrer, a xylene-filled Dean-Stark trap, and a condenser. PMDA (about 1.09 g, about 5 mmol) is then added to the amine solution, followed by stirring overnight to obtain a viscous solution. After stirring for about 3 hours, the solution is heated to reflux at about 200 °C for about 15 hours. During the polymerization process, water produced from the imidization is distilled from the reaction mixture along with about 1-2 mL of xylene. After cooling to ambient temperature, the solution is diluted with NMP and then slowly added to a vigorously stirred solution of 95% ethanol. The precipitated polymer is collected by filtration, washed with ethanol, and dried under reduced pressure at 150 °C. Before coating, the substrate (e.g., Pt electrode) is cleaned and optionally polished with an aqueous alumina slurry to about 0.05 μm. Then, about 20 μL of a polymer solution prepared by dissolving about 70 mg of polyimide in about 2 mL of NMP is dropped onto the surface of the Pt electrode and dried at room temperature for about 3 days. self-assembly techniques

[0284] Self-assembly processes can be used to build ultrathin multilayer films that contain alternating anionic and cationic polyelectrolytes on charged surfaces in succession. See, for example, Decher et al., Thin Solid Films, 210-211 (1992) 831-835. Ionic attraction between opposite charges is the driving force for multilayer construction. Contrary to chemisorption techniques that require approximately 100% reaction yield to maintain surface functional density in each layer, covalent bonds do not need to be formed in the self-assembly process. Furthermore, an advantage over classical Langmuir-Blodgett techniques is that solution processes are independent of the size and topology of the substrate. Exemplary polyelectrolytes for use in such processes include, but are not limited to, polystyrene sulfonate sodium salt, polyvinyl sulfonate potassium salt, poly-4-vinylbenzyl-(N,N-diethyl-N-methyl-)-ammonium iodide, and poly(allylamine hydrochloride). Construction of the multilayer film can be carried out as follows: A solid substrate with a positively charged planar surface is immersed in a solution containing an anionic polyelectrolyte and a monolayer of polyanions is adsorbed. Since the adsorption is carried out at a relatively high polyelectrolyte concentration, many ionic groups remain exposed at the interface with the solution, and thus the surface charge is reversed. After washing with pure water, the substrate is immersed in a solution containing a cationic polyelectrolyte. Again, a monolayer is adsorbed, but now the original surface charge is restored. By repeating both steps in a cyclic manner, an alternating multilayer assembly of both polymers is obtained. This process of multilayer formation is based on the attraction of opposite charges and therefore requires a minimum of two oppositely charged molecules. As a result, more than two molecules can be incorporated into the multilayer by simply immersing the substrate in as many polyelectrolyte solutions as desired, as long as the charges are reversed from layer to layer. Microoscillating multilayer assemblies can also be easily prepared. In this respect, the technique is more versatile than the Langmuir-Blodgett technique, which is rather limited to periodically alternating layer systems. Another advantage is that the immersion procedure does not impose major limitations with regard to substrate size or automation in a continuous process.

[0285] Specific examples of the preparation of such films are as follows: Polystyrene sulfonate (sodium salt, Mr=100,000) and polyvinyl sulfonate (potassium salt, Mr=245,000), and poly(allylamine hydrochloride), Mw=50,000-65,000) are obtained from commercial sources and used without further purification. Poly-4-vinylbenzyl-(N,N-diethyl-N-methyl-)-ammonium iodide can be synthesized as described in Decher et al., Ber. Bunsenges. Phys. Chem., 95 (1992) 1430. The alternating multilayer assemblies of all materials can be characterized by UV / visible spectroscopy and small angle X-ray scattering (SAXS) using techniques known in the art. Direct light microscopy and SAXS measurements can be performed with the multilayer assemblies on suitable substrates. The multilayer films can be deposited, for example, on platinum or other metal electrodes, or suitable intervening layers can be deposited on the electrodes. For the adsorption of the first layer, an aqueous acidic solution of polystyrene sulfonate or polyvinyl sulfonate can be used. The substrate is then washed with water. After adsorption of the first layer, the substrate can be stored for several weeks without significant deterioration of the surface. The cationic polyelectrolyte polyallylamine is then adsorbed from an aqueous solution. In the case of non-quaternized polyallylamine, the polycation is adsorbed from an acidic solution. All subsequent layers of anionic polyelectrolyte (odd layer numbers) are adsorbed from aqueous solutions. In the case of samples containing polyallylamine as a previously adsorbed layer, the polystyrene sulfonate layer can be adsorbed from an acidic solution. An adsorption time of about 20 minutes at ambient temperature can be used, although in certain embodiments, longer or shorter adsorption times can be acceptable. A range of polymer concentrations (e.g., 20-30 mg / about 10 mL of water) can provide acceptable results.

[0286] Multilayer molecular films of polyelectrolyte:calixarene and polyelectrolyte:cyclodextrin hosts can be fabricated by alternating adsorption of charged species in aqueous solution onto suitable substrates. See, for example, X. Yang, Sensors and Actuators B 45 (1997) 87-92. Using such layer-by-layer molecular deposition approach, molecular recognition reagents can be incorporated into polymer films. The deposition process is highly reproducible and the resulting films are uniform and stable. By substituting polyanions, highly negatively charged molecular species can be used in film fabrication. These molecular reagents can bind organic species and can be deposited into thin films as functional components. This approach results in films that incorporate polymer and molecular elements into the film, thus having the physical properties of polymers and the selectivity of molecular films. The films can be prepared as follows: The substrate (e.g., Pt electrode) can be first treated with aminopropyltrimethoxysilane in chloroform, followed by deposition of PSS and then PDDA polyelectrolyte by immersion in aqueous solutions of the respective polyelectrolytes. This can be followed by alternating depositions of a negatively charged molecular host species (e.g., calix[6]arene or pt-butylcalix[4]arene) and PDDA until the desired number of bilayers is reached. Between each deposition, the substrate is thoroughly washed with deionized water. Polyelectrolyte and molecular ion assembly can be monitored by UV-visible absorption spectroscopy, and mass loading can be measured with a surface acoustic wave (SAW) device.

[0287] In some embodiments, the interference domain is formed from one or more cellulose derivatives. Generally, cellulose derivatives can include polymers such as cellulose acetate, cellulose acetate butyrate, 2-hydroxyethyl cellulose, cellulose acetate phthalate, cellulose acetate propionate, cellulose acetate trimellitate, or blends and combinations thereof.

[0288] In some alternative embodiments, other polymeric types that may be utilized as the base material for the interference domain include polyurethanes and / or polymers with controlled pore sizes. In one such alternative embodiment, the interference domain includes a non-swelling, thin, hydrophobic membrane that limits the diffusion of low molecular weight species. The interference domain is permeable to relatively low molecular weight substances, such as hydrogen peroxide, but limits the passage of higher molecular weight substances, including glucose and ascorbic acid. Other systems and methods for reducing or eliminating interference species that may be applied to the membrane system of the preferred embodiments are described in U.S. Pat. No. 7,074,307, U.S. Patent Publication No. US-2005-0176136-A1, U.S. Pat. No. 7,081,195, and U.S. Patent Publication No. US-2005-0143635-A1, each of which is incorporated herein by reference in its entirety.

[0289] In some embodiments, it is contemplated that the thickness of the interference domain can be about 0.01 μm or less to about 20 μm or more. In some of these embodiments, the thickness of the interference domain can be about 0.01, about 0.05, about 0.1, about 0.15, about 0.2, about 0.25, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, about 1, about 1.5, about 2, about 2.5, about 3, or about 3.5 μm to about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, or about 19.5 μm. In some of these embodiments, the thickness of the interference domain can be from about 0.2, about 0.4, about 0.5, or about 0.6 microns to about 0.8, about 0.9, about 1, about 1.5, about 2, about 3, or about 4 microns.

[0290] Generally, the membrane systems described herein can be formed or deposited on exposed electroactive surfaces (e.g., one or more of the working and reference electrodes) using known thin film techniques (e.g., casting, spray coating, stretching, electrodeposition, dip coating, etc.), although casting or other known application techniques can also be utilized. In some embodiments, the interference domain can be deposited by spraying or dip coating. In one exemplary embodiment, the interference domain is formed by dip coating the sensor into the interference domain solution using an insertion rate of about 0.5 in / min to about 60 in / min, sometimes about 1 in / min, a residence time of about 0.01 min to about 2 min, sometimes about 1 min, and a withdrawal rate of about 0.5 in / min to about 60 in / min, sometimes about 1 in / min, and curing (drying) the domain for about 1 min to about 14 hours, sometimes about 3 min to about 15 min (which can also be accomplished at room temperature or under vacuum, e.g., about 20 to about 30 mmHg). In one exemplary embodiment including a cellulose acetate butyrate interference domain, a 3 minute cure (i.e., drying) time is used between each layer applied. In another exemplary embodiment using a cellulose acetate interference domain, a 15 minute cure time is used between each layer applied.

[0291] In some embodiments, the dipping process can be repeated at least once up to 10 times or more. In other embodiments, only one dipping is preferred. The preferred number of repeated dipping processes may depend on the cellulose derivative(s) used, their concentration, conditions during deposition (e.g., dipping), and the desired thickness (e.g., a thickness sufficient to provide functional blocking of a particular interferent), etc. In one embodiment, the interference domain is formed from three layers of cellulose acetate butyrate. In another embodiment, the interference domain is formed from ten layers of cellulose acetate. In yet another embodiment, the interference domain is formed from one layer of a blend of cellulose acetate and cellulose acetate butyrate. In alternative embodiments, the interference domain can be formed using any known method and combination of cellulose acetate and cellulose acetate butyrate, as will be appreciated by those skilled in the art. Electrode Domain

[0292] In some embodiments, such as the embodiment illustrated in FIG. 2A, an optional electrode domain 42, also referred to as an electrode layer, may be provided in addition to the biointerface domain, the diffusion resistance domain, and the enzyme domain, while in other embodiments it is contemplated that the functionality of the electrode domain may be incorporated into the biointerface domain to provide an integral domain that includes the functionality of the biointerface domain, the diffusion resistance domain, the enzyme domain, and the electrode domain.

[0293] In some embodiments, the electrode domain is located proximal to the electrochemically reactive surface. To facilitate the electrochemical reaction, the electrode domain may include a semi-permeable coating that maintains hydrophilicity at the electrochemically reactive surface of the sensor interface. The electrode domain may enhance the stability of adjacent domains by protecting and supporting the materials that form the adjacent domains. The electrode domain may also help stabilize the operation of the device by overcoming electrode starting and drift problems caused by inadequate electrolytes. The buffered electrolyte solution contained in the electrode domain may also protect against pH-mediated damage that may result from the formation of a large pH gradient between the electrode and a substantially hydrophobic interference domain due to the electrochemical activity of the electrode.

[0294] In some embodiments, the electrode domains are between about 0.05 μm and about 100 μm, sometimes between about 0.05, about 0.1, about 0.15, about 0.2, about 0.25, about 0.3, about 0.35, about 0.4, about 0.45, about 0.5, or about 1 μm to about 1.5, about 2, about 2.5, about 3, about 3.5, about 4, about 4.5, about 5, about 6, about 6.5, about 7, about 7.5, about 8, about 8.5, about 9 , about 9.5, about 10, about 10.5, about 11, about 11.5, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 19.5, about 20, about 30, about 40, about 50, about 60, about 70, about 80, about 90, or about 100 μm. In some embodiments, the thickness of the electrode domain can be from about 2, about 2.5, or about 3 μm to about 3.5, about 4, about 4.5, or about 5 μm for transdermally implanted sensors, or from about 6, about 7, or about 8 μm to about 9, about 10, about 11, or about 12 μm for entirely implanted sensors. As used herein, the term "dry film thickness" is a broad term given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, the thickness of a cured film cast from a coating formulation on the surface of a membrane by standard coating techniques. The coating formulation may include a premix of a film-forming polymer and a crosslinker, and may be curable upon application of moderate heat.

[0295] In certain embodiments, the electrode domains may be formed of a curable mixture of a urethane polymer and a hydrophilic polymer. In some of these embodiments, the coating is formed of a polyurethane polymer having anionic carboxylate functional groups and nonionic hydrophilic polyether segments, which is crosslinked in the presence of polyvinylpyrrolidone and cured at moderate temperatures of about 50° C.

[0296] Aqueous dispersions of fully reacted colloidal polyurethane polymers with crosslinkable carboxyl functionality (e.g., BAYBOND™, Mobay Corporation) are particularly suitable for this purpose. These polymers are supplied in dispersion grades with a polycarbonate-polyurethane backbone containing carboxylate groups identified as XW-121 and XW-123, and a polyester-polyurethane backbone containing carboxylate groups identified as XW-110-2. In some embodiments, BAYBOND™ 123, an aqueous anionic dispersion of an aliphatic polycarbonate urethane polymer sold as a 35% by weight solution in water and the cosolvent N-methyl-2-pyrrolidone, may be used.

[0297] In some embodiments, the electrode domain is formed from a hydrophilic polymer that renders the electrode domain equal to or more hydrophilic than the overlying domain (e.g., interference domain, enzyme domain). Such hydrophilic polymers can include, for example, polyamides, polylactones, polyimides, polylactams, functionalized polyamides, functionalized polylactones, functionalized polyimides, functionalized polylactams, or combinations thereof.

[0298] In some embodiments, the electrode domain is formed primarily from a hydrophilic polymer, and in some of these embodiments, the electrode domain is formed substantially from PVP. PVP is a hydrophilic water-soluble polymer, commercially available as the PVP K™ homopolymer series by BASF Wyandotte and GAF ​​Corporation, in a range of viscosity grades and average molecular weights ranging from about 18,000 to about 500,000. In certain embodiments, a PVP homopolymer having an average molecular weight of about 360,000, identified as PVP-K90 (BASF Wyandotte), can be used to form the electrode domain. Hydrophilic film-forming copolymers of N-vinylpyrrolidone are also suitable, such as copolymers of N-vinylpyrrolidone and vinyl acetate, copolymers of N-vinylpyrrolidone, ethyl methacrylate, and methacrylic acid monomers, and the like.

[0299] In certain embodiments, the electrode domain is entirely formed from a hydrophilic polymer. Useful hydrophilic polymers contemplated include, but are not limited to, poly-N-vinylpyrrolidone, poly-N-vinyl-2-piperidone, poly-N-vinyl-2-caprolactam, poly-N-vinyl-3-methyl-2-caprolactam, poly-N-vinyl-3-methyl-2-piperidone, poly-N-vinyl-4-methyl-2-piperidone, poly-N-vinyl-4-methyl-2-caprolactam, poly-N-vinyl-3-ethyl-2-pyrrolidone, poly-N-vinyl-4,5-dimethyl-2-pyrrolidone, polyvinyl imidazole, poly-N,N-dimethylacrylamide, polyvinyl alcohol, polyacrylic acid, polyethylene oxide, poly-2-ethyl-oxazoline, copolymers thereof, and mixtures thereof. Blends of two or more hydrophilic polymers may be suitable in some embodiments.

[0300] In certain embodiments, the hydrophilic polymer used may not be crosslinked, while in other embodiments, crosslinking is used and may be achieved by any of a variety of methods, for example, by adding a crosslinking agent. In some embodiments, the polyurethane polymer may be crosslinked in the presence of PVP by preparing a premix of the polymers and adding the crosslinking agent immediately prior to the formation of the membrane. Suitable crosslinking agents contemplated include, but are not limited to, carbodiimides (e.g., 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride, and UCARLNK™ XL-25 (Union Carbide)), epoxides, and melamine / formaldehyde resins. Alternatively, it is contemplated that crosslinking may be achieved by irradiation at a wavelength sufficient to promote crosslinking between hydrophilic polymer molecules, which is believed to create a more tortuous diffusion path through the domains.

[0301] The flexibility and rigidity of the coating can be varied as desired by varying the dry weight solids of the components in the coating formulation. As used herein, the term "dry weight solids" is a broad term, given its ordinary and customary meaning to those skilled in the art (and is not limited to any special or customized meaning), and refers to, but is not limited to, the dry weight percentage based on the total coating composition after the crosslinker is included. In one embodiment, the coating formulation can include, for example, about 6 to about 20 dry weight %, preferably about 8 dry weight %, PVP, about 3 to about 10 dry weight %, sometimes about 5 dry weight % crosslinker, and about 70 to about 91 wt %, sometimes about 87 wt % polyurethane polymer, e.g., polycarbonate-polyurethane polymer. The reaction product of such a coating formulation is referred to herein as a water-swellable crosslinked matrix of polyurethane and PVP.

[0302] In some embodiments, below the electrode domain is an electrolyte phase, which is a free liquid phase that contains a solution containing at least one compound, typically a soluble chloride salt that conducts electric current when hydrated. In one embodiment where the membrane system is used with a glucose sensor as described herein, the electrolyte phase flows over the electrode and contacts the electrode domain. It is contemplated that certain embodiments can use any suitable electrolyte solution, including standard commercially available solutions. In general, the electrolyte phase can have the same osmolality as the sample to be analyzed or a lower osmolality. In a preferred embodiment, the electrolyte phase comprises normal saline. Bioactive Agents

[0303] It is contemplated that any of a variety of bioactive (therapeutic) agents may be used with the analyte sensor systems described herein, such as the analyte sensor system shown in FIG. 1. In certain embodiments, the bioactive agent may be in the biointerface layer of the disclosed device. In some embodiments, the bioactive agent is an anticoagulant. As used herein, the term "anticoagulant" is a broad term and is given its ordinary and customary meaning to those of skill in the art (and is not limited to any special or customized meaning) and refers to, but is not limited to, a substance that prevents clotting (e.g., minimizes, reduces, or stops embolism of blood). In these embodiments, the anticoagulant included in the analyte sensor system may prevent clotting in or on the sensor.Anticoagulants suitable for incorporation into the sensor system include, but are not limited to, vitamin K antagonists (e.g., acenocoumarol, chlorindione, dicoumarol, diphenadione, ethyl viscoum acetate, phenprocoumon, phenindione, thiochromarol, or warfarin), heparin-based anticoagulants (e.g., platelet aggregation inhibitors: antithrombin III, bemiparin, dalteparin, danaparoid, enoxaparin, heparin, nadroparin, parnaparin, reviparin, sordexide, tinzaparin), other platelet aggregation inhibitors (e.g., abciximab, acetylsalicylic acid (aspirin), aloxiprine, beraprost, ditazol, carbasalar, etc.), and the like. thrombin inhibitors (e.g., argatroban, bivalirudin, desirudin, lepirudin, melagatran, ximelagatran), other antithrombotic agents (e.g., dabigatran, defibrotide, dermatan sulfate, fondaparinux, rivaroxaban), and the like.

[0304] In one embodiment, heparin is incorporated into the analyte sensor system, for example, by dipping or spraying. Without being bound by theory, heparin coated on the catheter or sensor can prevent blood from clumping and embolizing on the analyte sensor system, thereby preventing thromboembolization (e.g., prevention of blood flow by clots or clotting) or subsequent complications. In some embodiments, heparin is admixed with one or more zwitterionic compounds or derivatives thereof, such as hydrolyzable cationic esters thereof (described above), prior to dipping or spraying, thus providing a mixed coating of heparin and one or more zwitterionic compounds or derivatives thereof on the sensor system.

[0305] In some embodiments, an antimicrobial agent is coated on the catheter (inner or outer diameter) or on the sensor. In some embodiments, an antimicrobial agent may be incorporated into the analyte sensor system. Antimicrobial agents contemplated may include, but are not limited to, antibiotics, antiseptics, bactericides, and synthetic moieties, as well as combinations thereof, and other agents that are soluble in organic solvents, such as alcohols, ketones, ethers, aldehydes, acetonitrile, acetic acid, methylene chloride, and chloroform. The amount of each antimicrobial agent used to impregnate the medical device will vary to some extent, but will at least be a concentration effective to inhibit the growth of bacterial and fungal organisms, such as Staphylococcus aureus, Gram-positive bacteria, Gram-negative bacteria, and Candida.

[0306] In some embodiments, antibiotics may be incorporated into the analyte sensor system. Classes of antibiotics that may be used may include tetracyclines (e.g., minocycline), rifamycins (e.g., rifampin), macrolides (e.g., erythromycin), penicillins (e.g., napheline), cephalosporins (e.g., cefazolin), other β-lactam antibiotics (e.g., imipenem, aztreonam), aminoglycosides (e.g., gentamicin), chloramphenicol, sulfonamides (e.g., sulfamethoxazole), glycopeptides (e.g., vancomycin), quinolones (e.g., ciprofloxacin), fusidic acid, trimethoprim, metronidazole, clindamycin, mupirocin, polyenes (e.g., amphotericin B), azoles (e.g., fluconazole), and β-lactam inhibitors (e.g., sulbactam).

[0307] Examples of specific antibiotics that may be used include minocycline, rifampin, erythromycin, nafcillin, cefazolin, imipenem, aztreonam, gentamicin, sulfamethoxazole, vancomycin, ciprofloxacin, trimethoprim, metronidazole, clindamycin, teicoplanin, mupirocin, azithromycin, clarithromycin, ofloxacin, lomefloxacin, norfloxacin, nalidixic acid, sparfloxacin, pefloxacin, amifloxacin, enoxacin, fleroxacin, temafloxacin, tosufloxacin, clinafloxacin, sulbactam, clavulanic acid, amphotericin B, fluconazole, itraconazole, ketoconazole, and nystatin.

[0308] In some embodiments, preservatives or bactericides may be incorporated into the analyte sensor system. Examples of preservatives and bactericides are hexachlorophene, cationic bis-iguanides (e.g., chlorhexidine, cyclohexidine), iodines and iodophors (e.g., povidone-iodine), para-chloro-meta-xylenol, triclosan, furan medical preparations (e.g., nitrofurantoin, nitrofurazone), methenamine, aldehydes (glutaraldehyde, formaldehyde), and alcohol. Other examples of preservatives and bactericides will be readily suggested by those skilled in the art.

[0309] In some embodiments, anti-barrier cell agents may be incorporated into the analyte sensor system. Anti-barrier cell agents may include compounds that are effective against macrophages and foreign body giant cells (FBGCs). It is believed that anti-barrier cell agents prevent the closure of the barrier to lysate transport presented by macrophages and FBGCs at the device-tissue interface during FBC maturation. Anti-barrier cell agents may provide an anti-inflammatory or immunosuppressive mechanism that affects the wound healing process, for example, the healing of wounds created by incisions into which implantable devices are inserted. Cyclosporine, which stimulates very high levels of vascularization around biomaterials, may be incorporated into the biointerface membrane of preferred embodiments (see U.S. Patent No. 5,569,462 to Martinson et al.). Alternatively, dexamethasone, which attenuates the strength of the FBC response at the tissue-device interface, may be incorporated into the biointerface membrane of preferred embodiments. Alternatively, rapamycin, a potent specific inhibitor of some macrophage inflammatory functions, may be incorporated into the biointerface membrane of preferred embodiments.

[0310] In some embodiments, anti-inflammatory agents may be incorporated into the analyte sensor system to reduce acute or chronic inflammation adjacent to the implant or to reduce the formation of FBC capsules, for example, to reduce the formation of a barrier cell layer. Suitable anti-inflammatory agents include, but are not limited to, nonsteroidal anti-inflammatory drugs (NSAIDS), such as acetomethaphen, aminosalicylic acid, aspirin, celecoxib, choline magnesium trisalicylate, diclofenac potassium, diclofenac sodium, diflunisal, etodolac, fenoprofen, flurbiprofen, ibuprofen, indomethacin, interleukin (IL)-10, IL-6 muteins, anti-IL-6 iNOS inhibitors (e.g., L-NAME or L-NMDA), interferons, ketoprofen, ketorolac, leflunomide, melenamic acid, mycophenolic acid, mizoribine, nabumetone, naproxen, naproxen sodium, oxaprozin, Piroxicam, rofecoxib, salsalate, sulindac, and trimethine; and corticosteroids such as cortisone, hydrocortisone, methylprednisolone, prednisone, prednisolone, betamethasone, beclomethasone dipropionate, budesonide, dexamethasone sodium phosphate, flunisolide, fluticasone propionate, paclitaxel, tacrolimus, tranilast, triamcinolone acetonide, betamethasone, fluocinolone, betamethasone dipropionate, betamethasone valerate, desonide, desoximethasone, fluocinolone, triamcinolone, triamcinolone acetonide, clobetasol propionate, and dexamethasone.

[0311] In some embodiments, immunosuppressants or immunomodulators can be incorporated into the analyte sensor system to directly interfere with some important mechanisms essential for the involvement of different cellular elements in the inflammatory response. Suitable immunosuppressants and immunomodulators include, but are not limited to, antiproliferative cell cycle inhibitors (e.g., paclitaxel, cytochalasin D, infiximab), taxol, actinomycin, mitomycin, thospromote VEGF, estradiol, NO donors, QP-2, tacrolimus, tranilast, actinomycin, everolimus, methotrexate, mycophenolic acid, angiopeptin, vincristine, mitomycin, statins, C These include MYC antisense, sirolimus (and analogs), RestenASE, 2-chloro-deoxyadenosine, PCNA ribozyme, batimustat, prolyl hydroxylase inhibitors, PPARγ ligands (e.g., troglitazone, rosiglitazone, pioglitazone), halofuginone, C-proteinase inhibitors, probucol, BCP671, EPC antibodies, catchin, glycating agents, endothelin inhibitors (e.g., ambrisentan, tesosentan, bosentan), statins (e.g., cerivastine), E. coli heat labile enteroloxin, and advanced coatings.

[0312] In some embodiments, an anti-infective agent may be incorporated into the analyte sensor system. In general, an anti-infective agent is a substance that can act against infection by inhibiting the spread of infectious agents or by immediately killing infectious agents, and may function, for example, to reduce an immune response without an inflammatory response at the implantation site. Anti-infective agents include, but are not limited to, anthelmintics (e.g., mebendazole), antibiotics (e.g., aminoglycosides, gentamicin, neomycin, tobramycin), antifungal antibiotics (e.g., amphotericin b, fluconazole, glycerofulvin, itraconazole, ketoconazole, nystatin, micatin, tolnaftate), cephalosporins (e.g., cefaclor, cefazolin, cefotaxime, ceftazidime, ceftriaxone, cefuroxime, cephalexin), β-lactam antibiotics (e.g., cefotetan, meropenem), chloramphenicol, macrolides (e.g., azithromycin, clarithromycin, erythromycin), penicillins (e.g., penicillin G sodium salt, amoxicillin, ampicillin, dicloxacillin, nafcillin, pipera, cyclin, ticarcillin), tetracyclines (e.g., doxycycline, minocycline, tetracycline), bacitracin, clindamycin, colistin metasodium, polymyxin b sulfate, vancomycin, antivirals (e.g., acyclovir, amantadine, didanosine, efavirenz, foscarnet, ganciclovir, indinavir, lamivudine, nelfinavir, ritonavir, saquinavir, silver, stavudine, valacyclovir, valganciclovir, zidovudine), quinolones (e.g., ciprofloxacin, levofloxacin), sulfonamides (e.g., sulfadiazine, sulfisoxazole), sulfones (e.g., dapsone), furazolidone, metronidazole, pentamidine, sulfanilamidum crystallinum crystallinum, gatifloxacin, and sulfamethoxazole / trimethoprim.

[0313] In some embodiments, angiogenic agents may be incorporated into the analyte sensor system. Angiogenic agents may generally include substances with direct or indirect angiogenic properties. In some cases, angiogenic agents may additionally affect the formation of barrier cells in vivo. Indirect angiogenesis means that angiogenesis may be mediated through inflammatory or immune stimulatory pathways. It is not entirely known how agents that induce local angiogenesis inhibit barrier cell formation, but without being bound by theory, it is believed that some barrier cell stiffening may result indirectly from the effects of angiogenic agents.

[0314] Angiogenic agents may promote angiogenesis and accelerate wound healing around the membrane or provide a mechanism to minimize ischemic periods by increasing angiogenesis near the tissue-device interface. Sphingosine-1-phosphate (S1P), a phospholipid with potent angiogenic activity, may be incorporated into the biointerface membrane. Monobutyrin, a vasodilatory and angiogenic lipid product of adipocytes, may also be incorporated into the biointerface membrane. In another embodiment, an antisense molecule (e.g., thrombospondin-2 antisense) capable of increasing angiogenesis is incorporated into the biointerface membrane.

[0315] Angiogenic agents may provide a mechanism for promoting inflammation, which is believed to accelerate angiogenesis and wound healing in vivo. In one embodiment, a xenogeneic carrier, such as bovine collagen, whose foreign nature induces an immune response, stimulates angiogenesis and is incorporated into the biointerface membrane of some embodiments. In another embodiment, lipopolysaccharide, an immune stimulant, may be incorporated into the biointerface membrane. In another embodiment, proteins, such as bone morphogenetic proteins (BMPs), which regulate bone healing in tissues, may be incorporated into the biointerface membrane.

[0316] In some embodiments, angiogenic agents may be incorporated into the analyte sensor system. Angiogenic agents are substances that can stimulate angiogenesis, for example, accelerating and sustaining the development of a vascularized tissue bed at the tissue-device interface. Angiogenic agents include, but are not limited to, basic fibroblast growth factor (bFGF) (also known as heparin-binding growth factor-II and fibroblast growth factor II), acidic fibroblast growth factor (aFGF) (also known as heparin-binding growth factor-I and fibroblast growth factor-I), vascular endothelial growth factor (VEGF), platelet-derived endothelial growth factor BB (PDEGF-BB), angiopoietin-1, transforming growth factor beta (TGF-β), transforming growth factor alpha (TGFα), hepatocyte growth factor, tumor necrosis factor-alpha (TNFα), placental growth factor (PLGF), angiogenin, interleukin-8 (IL-8), hypoxia inducible factor-I (HIF-1), angiotensin-converting enzyme (ACE) inhibitor quinaprilat, angiotropin, thrombospondin, peptide KGHK, low oxygen tension, lactate, insulin, copper sulfate, estradiol, prostaglandins, cyclooxygenase inhibitors, endothelial cell binding agents (e.g., decorin or vimentin), glenipin, hydrogen peroxide, nicotine, and growth hormone.

[0317] In some embodiments, pro-inflammatory agents may be incorporated into the analyte sensor system. Pro-inflammatory agents are generally substances that can stimulate an immune response in the host tissue and can accelerate or sustain the formation of a mature vascularized tissue bed. For example, pro-inflammatory agents are generally irritants or other substances that induce chronic inflammation and chronic granular responses at the wound site. Without being bound by theory, it is believed that the formation of high tissue granularity induces blood vessels that provide adequate or abundant supply of analytes to the device-tissue interface. Pro-inflammatory agents include, but are not limited to, xenogeneic carriers, lipopolysaccharides, S. aureus peptidoglycan, and proteins.

[0318] These bioactive agents may be used alone or in combination. The bioactive agent may be dispersed throughout the material of the sensor, for example, incorporated into at least a portion of the membrane system or incorporated into the device (e.g., housing) and adapted to diffuse through the membrane.

[0319] There are various systems and methods by which a bioactive agent may be incorporated into the sensor membrane. In some embodiments, the bioactive agent may be incorporated during the manufacture of the membrane system. For example, the bioactive agent may be blended prior to curing the membrane system or following membrane system manufacture, for example, by coating, imbibing, solvent casting, or absorbing the bioactive agent into the membrane system. In some embodiments, the bioactive agent is incorporated into the membrane system, while in other embodiments, the bioactive agent may be administered simultaneously with, before, or after insertion of the device in vivo, for example, by oral administration or locally by subcutaneous injection near the implantation site. A combination of a bioactive agent incorporated into the membrane system and local or systemic bioactive agent administration may be preferred in certain embodiments.

[0320] In general, bioactive agents can be incorporated into the membrane system or can be adapted to diffuse out of the device to modify the host's in vivo response to the membrane. In some embodiments, the bioactive agent can be incorporated into only a portion of the membrane system adjacent to the sensing region of the device, over the entire surface of the device except on the sensing region, or any combination thereof, which can help control different mechanisms or stages of the in vivo response (e.g., embolization). However, in some alternative embodiments, the bioactive agent can be incorporated into the device proximal to the membrane system, whereby the bioactive agent diffuses through the membrane system into the host's circulatory system.

[0321] The bioactive agent includes a carrier matrix, where the matrix includes one or more of collagen, a particle matrix, an absorbent or non-absorbent matrix, a controlled release matrix, or a gel. In some embodiments, the carrier matrix includes a receptor, where the bioactive agent is encapsulated in a microcapsule. The carrier matrix may include a system in which the bioactive agent is physically entrapped within a polymer network. In some embodiments, the bioactive agent is crosslinked with the membrane system, while in other embodiments, the bioactive agent is absorbed into the membrane system, for example, by adsorption, absorption, or imbibition. The bioactive agent may be deposited in or on the membrane system, for example, by coating, filling, or solvent casting. In certain embodiments, the bioactive agent is incorporated into the membrane system using ionic and non-ionic surfactants, detergents, micelles, emulsifiers, demulsifiers, stabilizers, aqueous and oily carriers, solvents, preservatives, antioxidants, or buffers.

[0322] In some embodiments, the surface of the membrane system comprises a tie layer found on the outermost surface of the sensor membrane to which the bioactive agent reversibly binds. In some embodiments, the tie layer comprises one or more zwitterionic compounds, or precursors or derivatives thereof, which are bound to surface active groups of the polymer comprising the outermost domain of the membrane system. In some embodiments, the zwitterionic compound, or precursors or derivatives thereof, comprises one or more zwitterionic betaines, as described above. In some embodiments, the zwitterionic compound, or precursors or derivatives thereof, comprises a hydrolyzable cation ester of a zwitterionic compound, as described above. In a preferred embodiment, the tie layer comprises one or more hydrolyzable cation betaine esters, such as hydrolyzable cation pCB esters.

[0323] Bioactive agents can also be incorporated into a polymer using techniques such as those described above, and the polymer can be used to form a membrane system, a coating on a membrane system, part of a membrane system, or any part of a sensor system.

[0324] The membrane system can be manufactured using techniques known in the art. The bioactive agent can be absorbed into the membrane system, for example, by soaking the membrane system for a length of time (e.g., from about 1 hour or less to about 1 week, or more preferably from about 4, about 8, about 12, about 16, or about 20 hours to about 1, about 2, about 3, about 4, about 5, or about 7 days).

[0325] The bioactive agent may be blended into the uncured polymer prior to forming the membrane system, which is then cured, whereby the bioactive agent becomes crosslinked or encapsulated within the polymer that forms the membrane system.

[0326] In yet another embodiment, microspheres are used to encapsulate bioactive agents. The microspheres may be formed of biodegradable polymers, most preferably synthetic or natural polymers, such as proteins and polysaccharides. As used herein, the term polymer is used to refer to both synthetic polymers and proteins. U.S. Pat. No. 6,281,015 discloses several systems and methods that may be used with the preferred embodiments. In general, the bioactive agent may be incorporated into (1) the polymer matrix that forms the microsphere, (2) the microparticle(s) surrounded by the polymer that forms the microsphere, (3) the polymer core within the protein microsphere, (4) the polymer coating around the polymer microsphere, (5) mixed with the microspheres that are aggregated into a larger form, or (6) a combination thereof. The bioactive agent may be incorporated as a particle or by co-dissolving the factor with the polymer. Stabilizing agents may be incorporated by addition of the stabilizing agent to the factor solution prior to the formation of the microspheres.

[0327] The bioactive agent may be incorporated into, coated on, or otherwise deposited within or on the membrane system. Some hydrogels suitable for use in preferred embodiments contain a crosslinked, hydrophilic, three-dimensional polymer network that is highly permeable to the bioactive agent and can be triggered to release the bioactive agent upon a stimulus.

[0328] The bioactive agent can be incorporated into the membrane system by solvent casting, where a solution containing the dissolved bioactive agent is deposited onto the surface of the membrane system, and the solvent is then removed to form a coating on the membrane surface.

[0329] The bioactive agent may be complexed to a plug of material located within the device, such as those described in U.S. Patent No. 4,506,680 and U.S. Patent No. 5,282,844. In some embodiments, it is preferred to place this plug beneath the membrane system, thus allowing the bioactive agent to be controlled by diffusion through the membrane, providing a mechanism for sustained release of the bioactive agent in the host. Bioactive Agent Release

[0330] Many variables can affect the pharmacokinetics of bioactive agent release. The bioactive agents of the preferred embodiments may be optimized for short-term or long-term release. In some embodiments, the bioactive agents of the preferred embodiments are designed to aid or overcome factors associated with short-term effects of sensor insertion (e.g., acute inflammation or embolism). In some embodiments, the bioactive agents of the preferred embodiments are designed to aid or overcome factors associated with long-term effects, such as chronic inflammation or the build-up of fibrotic tissue or plaque material. In some embodiments, the bioactive agents of the preferred embodiments combine short-term and long-term release to take advantage of the benefits of both.

[0331] As used herein, "controlled," "sustained," or "prolonged" release of a factor can be continuous or intermittent, linear or non-linear. This can be achieved using one or more polymer compositions, drug loading, selection of excipients or degradation enhancing agents, or other modifications, and can be administered alone, in combination, or sequentially to produce the desired effect.

[0332] Short term release of a bioactive agent in preferred embodiments generally refers to release over a period of about a few minutes or hours to about 2, about 3, about 4, about 5, about 6, or about 7 days or more. Bioactive agent loading

[0333] The amount of bioactive agent loading into the membrane system may depend on several factors. For example, the dosage and duration of the bioactive agent may vary depending on the intended use of the membrane system, such as the intended duration of device use, differences in effective doses of the bioactive agent between patients, the location and method of loading the bioactive agent, and the release rates associated with the bioactive agents and, optionally, their carrier matrix. Thus, one of ordinary skill in the art will appreciate the variability in loading levels of bioactive agents for the reasons stated above.

[0334] In some embodiments in which the bioactive agent is incorporated into the membrane system without a carrier matrix, the preferred level of loading of the bioactive agent into the membrane system may vary depending on the nature of the bioactive agent. The loading level of the bioactive agent is preferably high enough for a biological effect (e.g., embolic protection) to be observed. Above this threshold, the bioactive agent may be loaded into the membrane system to assimilate up to 100% of the solid portion, coat all accessible surfaces of the membrane, or fill up to 100% of the accessible cavity space. Typically, the loading level is about 1 ppm or less to about 1000 ppm or more, preferably about 2, about 3, about 4, or about 5 ppm to up to about 10, about 25, about 50, about 75, about 100, about 200, about 300, about 400, about 500, about 600, about 700, about 800, or about 900 ppm (based on the weight of the bioactive agent(s), membrane system, and other materials present). In certain embodiments, loading levels can be from about 1% or less up to about 50% or more by weight, preferably from about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 15, or about 20% by weight up to about 25, about 30, about 35, about 40, or about 45% by weight.

[0335] When the bioactive agent is incorporated into the membrane system with a carrier matrix such as a gel, the gel concentration can be optimized, for example, loaded with one or more test loads of bioactive agent. It is generally preferred that the gel contains about 0.1 or less to about 50% or more by weight of bioactive agent(s), preferably about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, or about 0.9% by weight to about 6, about 7, about 8, about 9, about 10, about 15, about 20, about 25, about 30, about 35, about 40, or about 45% by weight or more of bioactive agent(s), more preferably about 1, about 2, or about 3% by weight to about 4 or about 5% by weight of bioactive agent(s). Non-biologically active substances can also be incorporated into the matrix.

[0336] Referring now to microencapsulated bioactive agents, release of the agent from these polymer systems generally occurs by two different mechanisms. The bioactive agent can be released by diffusion through aqueous fill channels created in the dosage form by dissolution of the agent, or by voids created by removal of the polymer solvent or pore former during the original microencapsulation. Alternatively, release can be enhanced due to degradation of the encapsulating polymer. Over time, the polymer erodes, creating more porosity and microstructure within the device. This creates additional pathways for release of the bioactive agent.

[0337] In some embodiments, the sensor is designed to be bioinert, for example, by using a bioinert material. The bioinert material does not substantially provoke any response from the host. As a result, cells may live adjacent to the material but do not form bonds with it. Bioinert materials include, but are not limited to, alumina, zirconia, titanium oxide, or other bioinert materials commonly used in the "catheter / catheterization" art. Without wishing to be bound by theory, it is believed that the inclusion of a bioinert material in or on the sensor may reduce adhesion of blood cells or proteins to the sensor, embolization, or other host responses to the sensor. EXAMPLES

[0338] Example 1: Sensors were prepared that contained a diffusion-resistant layer comprising a blend of PVP and a polyurethaneurea-polycarbonate block copolymer with or without silicone. The block copolymer with silicone exhibited the T g The tensile strength of the two block copolymers is shown in Figure 6A, and the puncture resistance is shown in Figure 6B. The sensitivity of the sensor was measured over 200 hours in an in vitro model, and the results are shown in Figure 4. The high T g The sensors with the polymer without the high tensile strength silicone had minimal drift (less than 10%) over the course of this experiment compared to the sensors with the lower Tg and tensile strength and silicone.

[0339] Additionally, the sensor noise was determined and the data are shown in Figures 9A and 9B. g And the sensors with the polymer without the high tensile strength silicone exhibited less in vivo noise in this 14-day study.

[0340] Example 2: Sensors were prepared that contained a diffusion-resistant layer comprising a blend of PVP and polyurethaneurea-polycarbonate block copolymer with or without silicone. The sensitivity of the sensors was tested in an in vivo pig model. At 7 and 14 days, the sensors were removed and analyzed to determine the percent rupture. The data is shown in Figure 7. Regarding the resistance layer mechanical properties of the sensors, in vivo stability testing demonstrated a mechanically robust high T g 4 shows that the polymer-based resistive layer has a lower rupture rate.

[0341] Example 3: Sensors were prepared with a diffusion-resistant layer comprising a blend of PVP and polyurethaneurea-polycarbonate block copolymer without silicone. In one sample, the sensor was immersed in distilled water at 50°C for various time intervals and then cured. In another sample, the sensor was cured without immersion. The results are shown in Figure 10. Immersion curing eliminated drift from the CalCheck. Figure 10 shows the results of a control sensor prepared from a RL with silicone and the high T shown in Figure 5. g 10. Comparison of sensor sensitivity drift between test sensors made of polycarbonate urethane-1, RL of 1000 and 10000 μg / dL. The sensors were exposed to a buffer solution with a constant glucose concentration (300 mg / dL) and their sensitivity was measured after subtracting the background signal and monitored for up to 14 days. The sensitivity change over the 2-hour time point was calculated and plotted in FIG. 10. As can be seen, the high T g Sensors prepared from RLs with silicone experienced a much smaller magnitude drift compared to sensors prepared from RLs with silicone.

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[0344] Methods and devices suitable for use in conjunction with aspects of the preferred embodiments are disclosed in U.S. application Ser. No. 09 / 447,227, filed Nov. 22, 1999, entitled "DEVICE AND METHOD FOR DETERMINING ANALYTE LEVELS," and U.S. application Ser. No. 13 / 461,625, filed May 1, 2012, entitled "DUAL ELECTRODE SYSTEM FOR A CONTINUOUS ANALYTE SENSOR."

[0345] For ease of explanation and illustration, in some instances, the detailed description describes the exemplary systems and methods in the context of a continuous glucose monitoring environment, but it should be understood that the scope of the invention is not limited to that particular environment, and that those skilled in the art will appreciate that the systems and methods described herein may be embodied in a variety of forms. Thus, any structural and / or functional details disclosed herein should not be construed as limiting the systems and methods, but rather are provided as attributes of representative embodiments and / or arrangements that may be advantageous in other settings to teach those skilled in the art one or more ways to implement the systems and methods.

[0346] For example, but not limited to, the described monitoring systems and methods may include sensors that measure concentrations of one or more analytes (e.g., glucose, lactate, potassium, pH, cholesterol, isoprene, and / or hemoglobin) and / or other blood or bodily fluid constituents in or relating to a host and / or another individual.

[0347] By way of example, and without limitation, embodiments of the monitoring systems and methods described herein may include fingerstick blood sampling, blood analyte test strips, non-invasive sensors, wearable monitors (e.g., smart bracelets, smart watches, smart rings, smart necklaces or pendants, workout monitors, fitness monitors, health and / or medical monitors, clip-on monitors, etc.), adhesive sensors, smart textiles and / or clothing integrated sensors, shoe inserts and / or insoles containing sensors, transdermal (i.e., transcutaneous) sensors, and / or swallowed, inhaled, or implantable sensors.

[0348] In some embodiments, without limitation, the monitoring systems and methods may include, instead of or in addition to the sensors described herein, inertial measurement units including accelerometers, gyroscopes, magnetometers, and / or barometers; movement, altitude, position, and / or location sensors; biometric sensors; optical sensors including, for example, optical heart rate monitors, photoplethysmogram (PPG) / pulse oximeters, fluorescence monitors, and cameras; wearable electrodes; electrocardiogram (EKG or ECG), electroencephalography (EEG), and / or electromyography (EMG) sensors; chemical sensors; flexible sensors, for example, for measuring extension, movement, pressure, weight, or impact; other sensors such as galvanometric sensors, capacitive sensors, electromagnetic field sensors, temperature / heat sensors, microphones, vibration sensors, ultrasonic sensors, piezoelectric / piezoresistive sensors, and / or transducers for measuring or information about the host and / or another individual.

[0349] While the present disclosure has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description should be considered as illustrative or exemplary and not restrictive. The present disclosure is not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art from a study of the drawings, the disclosure, and the appended claims in practicing the claimed disclosure.

[0350] All references cited herein are incorporated herein by reference in their entirety. To the extent that publications and patents or patent applications incorporated by reference conflict with the disclosure contained herein, the present specification is intended to supersede and / or take precedence over any such conflicting material.

[0351] Unless otherwise defined, all terms (including technical and scientific terms) shall have their ordinary and customary meanings as indicated to those skilled in the art, and shall not be limited to any special or customized meanings unless expressly defined as such herein. It should be noted that the use of a particular term when describing a particular feature or embodiment of the present disclosure should not be interpreted as implying that the term is redefined herein to include any particular characteristic of the feature or embodiment of the present disclosure to which it pertains. Particularly in the appended claims, the terms and phrases used in this application, and variations thereof, should be interpreted as open-ended as opposed to limiting, unless expressly stated otherwise. As examples of the above, the term "including" should be interpreted to mean "including without limitation," "including but not limited to," etc.; the term "comprising," as used herein, is synonymous with "including," "containing," or "featuring," is inclusive or open-ended, and does not exclude additional, unrecited elements or method steps; the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," the term "example" is used to provide illustrative examples of the items under discussion rather than an exhaustive or exclusive list of those items, and should not be construed as including "known," "conventional," "ordinary," or "common"; Adjectives such as "," "standard," and terms of similar import should not be construed to limit the subject matter described to that available in a given period or at a given time, but rather should be construed to encompass known, conventional, or standard technology that may be available or known at any time now or in the future, and the use of terms such as "preferably," "preferred," "desired," or "desirable" and terms of similar import should not be understood to imply that a particular feature is critical, essential, or even important to the structure or function of the invention, but rather should be intended merely to highlight alternative or additional features that may or may not be utilized in a particular embodiment of the invention.Similarly, groups of items joined by the conjunction "and" should not be construed as requiring the presence of every single one of those items in the group, but rather, unless otherwise stated, should be construed as "and / or." Similarly, groups of items joined by the conjunction "or" should not be construed as requiring mutual exclusivity between the groups, but rather, unless otherwise stated, should be construed as "and / or."

[0352] When a range of values ​​is provided, it is understood that the upper and lower limits, and each intervening value between the upper and lower limits of that range, are included within an embodiment.

[0353] With respect to virtually any plural and / or singular term herein, one skilled in the art can convert from plural to singular and / or from singular to plural as appropriate to the context and / or application. Various singular / plural permutations may be expressly set forth herein for clarity. The indefinite articles "a" or "an" do not exclude plurals. A single processor or other unit may accomplish the functions of several items recited in the claims. The mere fact that certain criteria are recited in mutually distinct independent claims does not indicate that a combination of these criteria cannot be used to advantage. Reference signs in the claims should not be construed as limiting the scope.

[0354] It will be further understood by those skilled in the art that, when a specific number is intended in an introduced claim recitation, such intent shall be clearly stated in the claim, and that in the absence of such a statement, no such intent exists. For example, to aid in understanding, the following appended claims may include the use of the introductory phrases "at least one" and "one or more" to introduce the claim recitation. However, the use of such phrases should not be construed as implying that the introduction of a claim recitation with the indefinite article "a" or "an" limits a particular claim that includes such an introduced claim recitation to an embodiment that includes only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and an indefinite article such as "a" or "an" (e.g., "a" and / or "an" should typically be construed to mean "at least one" or "one or more"), which also applies to the use of definite articles used to introduce claim recitations. In addition, even if a specific number of recitations of an introduced claim is explicitly recited, a person skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., a mere recitation of "two recitations" without other modifiers typically means at least two recitations, or more than two recitations). Furthermore, when a conventional expression similar to "at least one of A, B, or C, etc." is used, such a structure is generally intended in the sense that a person skilled in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.). When a conventional expression similar to "at least one of A, B, or C, etc." is used, such a structure is generally intended in the sense that one of ordinary skill in the art would understand the conventional expression (e.g., "a system having at least one of A, B, or C" includes, but is not limited to, systems having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, and C, etc.).It will be further understood by those skilled in the art that virtually any disjunction and / or phrase indicating two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" is understood to include the possibilities of "A" or "B" or "A and B."

[0355] It is to be understood that all numbers expressing quantities of ingredients, reaction conditions, and the like used herein are in all instances modified by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of any claims in any application claiming priority to this application, each numerical parameter should be construed in light of the number of significant digits and ordinary rounding approaches.

[0356] Moreover, while the foregoing has been described in some detail by way of illustration and example for purposes of clarity and understanding, it will be apparent to those skilled in the art that certain changes and modifications may be practiced. Thus, the description and examples should not be construed as limiting the scope of the invention to the specific embodiments and examples described herein, but rather as embracing all modifications and alternatives that fall within the true scope and spirit of the invention.

Claims

[Claim 1] 1. A device for the measurement of an analyte concentration, said device comprising: a sensor configured to generate a signal related to the concentration of an analyte; a sensing membrane located over the sensor, the sensing membrane comprising a diffusion resistant layer comprising a base polymer having a minimum glass transition temperature measured using ASTM D3418 of greater than -50°C.

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