Measuring glucose near the insulin delivery catheter by minimizing the adverse effects of insulin preservatives: Alternative ligands and redox mediator metals

Abstract

A device for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentrations may include a hollow tube and an amperometric glucose sensor positioned proximal to the distal end of the hollow tube. The amperometric glucose sensor may include a redox mediator and an enzyme including glucose oxidase or glucose dehydrogenase. The applied bias potential may prevent the electrode layer of the amperometric glucose sensor from substantially undergoing electropolymerization of the excipients of the insulin or insulin analog formulation during continuous operation of the amperometric glucose sensor. The sensitivity of the amperometric glucose sensor to subcutaneous glucose concentrations may be maintained in the presence of insulin or insulin analog formulations.

Description

[Technical Field]

[0001] cross reference

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 069,088, filed August 23, 2020, which is incorporated by reference in its entirety into this specification. [Background technology]

[0002]

[0002] Subjects with diabetes may be at risk of developing complications, such as kidney disease, eye disease, cardiovascular disease, and foot / nerve disease. Subjects who require insulin treatment may have more difficulty controlling their glucose levels compared to subjects who do not require insulin treatment. Subjects with type 1 diabetes (T1D) may require insulin, and many such subjects have received insulin using a continuous pump, which allows for accurate and controlled delivery of insulin 24 hours a day. Summary of the Invention

[0003]

[0003] A valuable technology in the management of T1D is continuous glucose monitoring (GCM), in which a subcutaneously inserted sensor provides the user with interstitial glucose data every few minutes. For example, a JDRF-sponsored study showed that subjects of all ages who regularly used CGMs experienced better glycemic control (e.g., as measured by hemoglobin A1C (A1C)) than non-users. However, many subjects may find CGM use intrusive, and many may only use CGMs sporadically. Not surprisingly, CGM use may not translate to better glycemic control when used sporadically or infrequently.

[0004] Daily life can be difficult for people who regularly use both an insulin pump and a CGM. Such individuals may need to carry two skin-penetrating devices, which may increase the risk of pain, infection, and other side effects compared to a single device. Individuals with T1D may carry multiple devices on their bodies, such as pumps and / or syringes, CGM receivers, vials of insulin, blood glucose monitors for calibrating the CGM, and blood glucose monitoring strips and lancets. Device multiplicity can lead to a situation known as “device burden,” which can lead to frustration, anger, and a patient choosing between devices rather than utilizing all the devices that could improve their health.

[0005]

[0005] Recognizing the challenges encountered in clinical care and management due to issues related to device burden, the present disclosure addresses the unmet need to integrate a CGM and insulin pump cannula into a single device.

[0006]

[0006] Manufacturers' instructions may state that subcutaneous glucose sensors must be placed far from the insulin pump cannula site. Supporting this statement, during porcine studies, we found that current insulin formulations significantly interfere with currently available hydrogen peroxide-measuring sensors. More specifically, we found that preservatives in the formulations, such as phenol and m-cresol, are electroactive and interfere with CGM.

[0007]

[0007] The present disclosure provides a device in which a glucose sensor can be successfully integrated with an insulin cannula, and methods for using the same. Such glucose sensors and insulin cannulas may be described, for example, by U.S. Patent No. 10,780,222, which disclosed osmium as the redox mediator element and pyridine- and imidazole-based ligands bound to osmium. The disclosed devices and methods can use alternative metals and alternative ligands, each of which can be used as a redox mediator.

[0008]

[0008] In one aspect, the present disclosure provides a device for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentrations, the device comprising: a hollow tube having a proximal end and a distal end, the proximal end being in fluid communication with a source of insulin or insulin analog formulation and the distal end being designed to deliver the insulin or insulin analog formulation subcutaneously, the insulin or insulin analog formulation comprising an excipient comprising phenol or cresol; and an amperometric glucose sensor positioned no more than a predetermined distance from the distal end, the amperometric glucose sensor comprising: an electrode layer comprising at least one indicator electrode, the electrode layer underlying a redox catalyst layer comprising (1) a redox mediator comprising a metal compound covalently bound to a ligand and (2) an enzyme comprising glucose oxidase or glucose dehydrogenase.

[0009] In some embodiments, the amperometric glucose sensor is positioned not more than 15 millimeters (mm) from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 14 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 13 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 12 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 11 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 10 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 9 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 8 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 7 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 6 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 5 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 4 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 3 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 2 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 1 millimeter (mm) from the distal end.

[0010] In some embodiments, the device further comprises a housing including an upper accessible surface and a lower surface designed to be attached to a skin surface. In some embodiments, the amperometric glucose sensor is disposed on a second hollow tube including a second distal end, wherein the second distal end is designed to be inserted subcutaneously. In some embodiments, the at least one indicator electrode comprises gold, carbon, graphite, platinum, or iridium. In some embodiments, the ligand is pyridine-based. In some embodiments, the ligand is 4,4'-dimethyl-2,2'-bipyridine. In some embodiments, the ligand is imidazole-based. In some embodiments, the redox mediator is bound to poly(4-vinylpyridine). In some embodiments, the redox mediator is bound to poly(1-vinylimidazole). In some embodiments, the excipient comprises phenol. In some embodiments, the excipient comprises cresol. In some embodiments, the amperometric sensor further comprises a reference electrode. In some embodiments, the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. In some embodiments, the amperometric sensor further comprises an insulating layer and a metal layer, wherein the insulating layer is coupled to the metal layer, and wherein the metal layer is coupled to the electrode layer. In some embodiments, the insulating layer comprises a polyimide or a liquid crystal polymer. In some embodiments, the metal layer has a thickness of at least about 1 micrometer (μm), 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. In some embodiments, the metal layer has a thickness of at least about 2 μm. In some embodiments, the metal layer comprises titanium, gold, or platinum. In some embodiments, the electrode layer comprises a thin film having a thickness not exceeding about 1000 nanometers (nm), 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm. In some embodiments, the electrode layer comprises a thin film having a thickness of less than about 500 nm. In some embodiments, the metal compound comprises a metal selected from the group consisting of osmium, ruthenium, iridium, iron, cobalt, and any combination thereof.

[0011] In some embodiments, the redox mediator and enzyme enable sufficient electron transfer from subcutaneous glucose to the at least one indicator electrode to cause the amperometric glucose sensor to respond to subcutaneous glucose concentrations at an applied bias potential not exceeding about +250 millivolts (mV), +200 mV, +150 mV, +100 mV, or +50 mV relative to the reference electrode. In some embodiments, an applied bias potential not exceeding about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV relative to the reference electrode enables the electrode layer to substantially not undergo electropolymerization of the excipients during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining the sensitivity of the amperometric glucose sensor to subcutaneous glucose concentrations in the presence of insulin or insulin analog formulations.

[0012] In some embodiments, the metal compound comprises a metal selected from the group consisting of the following metals: osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. In some embodiments, the metal compound comprises a metal selected from the group consisting of the following metals: ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper.

[0013] In some embodiments, the ligand comprises a heterocyclic nitrogen compound, a pyridine ring combined with an imidazole ring, a non-nitrogen element substituted in the heterocyclic ring, or a pendant "R" group attached to the heterocyclic ring. In some embodiments, the heterocyclic nitrogen compound comprises a pyridine or imidazole having one, two, three, or four rings.

[0014] In another aspect, the present disclosure provides a method for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentrations, comprising the steps of: (a) obtaining a device for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentrations, wherein the device comprises: (i) a hollow tube comprising a proximal end and a distal end, wherein the proximal end is in fluid communication with a source of insulin or insulin analog formulation and the distal end is designed to deliver the insulin or insulin analog formulation subcutaneously, wherein the insulin or insulin analog formulation comprises an excipient comprising phenol or cresol; and (ii) providing a hollow tube from the distal end an amperometric glucose sensor positioned no greater than a predetermined distance from the subject, wherein the amperometric glucose sensor comprises: an electrode layer comprising at least one indicator electrode, wherein the electrode layer underlies a redox catalyst layer comprising (1) a redox mediator comprising a metal compound covalently bound to a ligand and (2) an enzyme comprising glucose oxidase or glucose dehydrogenase; (b) connecting the proximal end of the hollow tube to a source of insulin or an insulin analog formulation; (c) subcutaneously inserting the distal end of the hollow tube into the subject; and (d) simultaneously (1) subcutaneously delivering insulin or an insulin analog formulation to the subject and (2) measuring the subcutaneous glucose concentration of the subject.

[0015] In some embodiments, the amperometric glucose sensor is positioned not more than 15 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 14 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 13 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 12 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 11 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 10 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 9 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 8 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 7 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 6 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned not more than 5 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 4 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 3 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 2 mm from the distal end. In some embodiments, the amperometric glucose sensor is positioned no more than 1 millimeter (mm) from the distal end.

[0016] In some embodiments, the device further comprises a housing comprising an upper accessible surface and a lower surface, and the method further comprises attaching the lower surface to the skin surface of the subject. In some embodiments, the amperometric glucose sensor is disposed on a second hollow tube comprising a second distal end, wherein the second distal end is designed to be inserted subcutaneously. In some embodiments, the at least one indicator electrode comprises gold, carbon, graphite, platinum, or iridium. In some embodiments, the ligand is pyridine-based. In some embodiments, the ligand is 4,4'-dimethyl-2,2'-bipyridine. In some embodiments, the ligand is imidazole-based. In some embodiments, the redox mediator is bound to poly(4-vinylpyridine). In some embodiments, the redox mediator is bound to poly(1-vinylimidazole). In some embodiments, the excipient comprises phenol. In some embodiments, the excipient comprises cresol. In some embodiments, the amperometric sensor further comprises a reference electrode. In some embodiments, the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. In some embodiments, the amperometric sensor further comprises an insulating layer and a metal layer, wherein the insulating layer is bonded to the metal layer, and wherein the metal layer is bonded to the electrode layer. In some embodiments, the insulating layer comprises a polyimide or a liquid crystal polymer. In some embodiments, the metal layer has a thickness of at least about 1 micrometer (μm), 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. In some embodiments, the metal layer has a thickness of at least about 2 μm. In some embodiments, the metal layer comprises titanium, gold, or platinum. In some embodiments, the electrode layer comprises a thin film having a thickness not exceeding about 1000 nanometers (nm), 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm. In some embodiments, the electrode layer comprises a thin film having a thickness of less than about 500 nm. In some embodiments, the metal compound comprises a metal selected from the group consisting of osmium, ruthenium, iridium, iron, cobalt, and any combination thereof.

[0017] In some embodiments, the method further comprises applying a bias potential not exceeding about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV relative to a reference electrode, wherein the redox mediator and enzyme enable sufficient electron transfer from subcutaneous glucose to the at least one indicator electrode to cause a response of the amperometric glucose sensor to subcutaneous glucose concentrations at the applied bias potential. In some embodiments, the applied bias potential enables the electrode layer to substantially not undergo electropolymerization of the excipients during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining the sensitivity of the amperometric glucose sensor to subcutaneous glucose concentrations in the presence of insulin or insulin analog formulations.

[0018] In some embodiments, the metal compound comprises a metal selected from the group consisting of the following metals: osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. In some embodiments, the metal compound comprises a metal selected from the group consisting of the following metals: ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper.

[0019] In some embodiments, the ligand comprises a heterocyclic nitrogen compound, a pyridine ring combined with an imidazole ring, a non-nitrogen element substituted in the heterocyclic ring, or a pendant "R" group attached to the heterocyclic ring. In some embodiments, the heterocyclic nitrogen compound comprises a pyridine or imidazole having one, two, three, or four rings.

[0020] In some embodiments, the subject has type 1 diabetes.

[0021] Additional aspects and advantages of the present disclosure will become readily apparent to those skilled in the art from the following detailed description, wherein only illustrative embodiments of the present disclosure are shown and described. As will be realized, the present disclosure is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present disclosure. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

[0021] Incorporation by Reference

[0022] All publications, patents, and patent applications mentioned herein are incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. To the extent that the 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.

[0022]

[0023] The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings (also referred to herein as "Figures" and "FIGs"), in which: [Brief explanation of the drawings]

[0023] [Figure 1]

[0024] Figure 1 (graph) shows the current obtained from a platinum electrode polarized at 600 mV. The initial response to hydrogen peroxide is normal and stable. Subsequent responses to increasing amounts of insulin formulations containing phenolic preservatives initially show a positive (oxidative) response followed by a continuous decrease in current, typical of electrode poisoning caused by electropolymerization. [Figure 2]

[0025] Figure 2 (bar graph) shows the electrochemical behavior of phenol and m-cresol at bare electrodes polarized at many different bias potentials. Very high oxidation currents are observed, especially at the highly positive potentials typical of those used for peroxide detection. For both phenol and cresol, the oxidation current decreases significantly as the bias potential is lowered. The appearance of such data obtained at platinum and gold electrodes is very similar. The data shown here are for a gold electrode. [Figure 3]

[0026] Figure 3 shows the structural formula of a polymer repeat unit (poly(l-vinylimidazole)) 1 (abbreviated PVI-MRMMG-DiMeBPY) bound to a member of the redox mediator metal group (defined below) 4, bearing two 4,4'-dimethyl,2,2'-bipyridine moieties 2 and 3. [Figure 4]

[0027] Figure 4 (graph) compares the incremental change in current density of two types of glucose oxidase-based sensors after exposure to a high dose of mixed phenols (total concentration 180 μg / mL, consisting of equal parts by weight of phenol and m-cresol) for 20 minutes in the presence of 5 mM glucose. Over this period, there was a significant decrease in current density 5 for each of the three platinum sensors. The bias potential for these sensors was 600 mV. In contrast, there was only a very small change in current density 6 for each of the three gold sensors coated with glucose oxidase and a redox mediator bound to a ligand and a polymer and biased at 180 mV. [Figure 5]

[0028] Figure 5 (graph) shows a series of amperometric responses of a gold sensor coated with glucose oxidase and a redox mediator bound to a ligand and a polymer to successively increasing glucose concentrations in a stirred phosphate buffer solution sparged with argon. The response to glucose over this concentration range is largely linear. [Figure 6]

[0029] Figure 6 (graph) shows the amperometric signal 7 (small closed symbols) and glucose level 8 (large open symbols) obtained from a glucose oxidase-based hydrogen platinum sensor biased at 600 mV in pigs. When lispro insulin was given at 105 minutes (indicated by the arrow), the preservative in this formulation led to an immediate and very high oxidation reaction, followed by electropolymerization poisoning of the electrode. The poisoning is evident toward the end of the experiment, where the amperometric signal is minimal despite very high glucose levels. [Figure 7]

[0030] Figure 7 (graph) shows the amperometric signal 9 and glucose level 10 obtained in pigs from a gold-based sensor coated with glucose oxidase cross-linked with glutaraldehyde and biased at 180 mV, and a redox mediator bound to the ligand and to the polymer. Lispro insulin was given at 105 min (indicated by the arrow), and there was no change in the amperometric signal 9, despite the high level of preservatives in this formulation. Of note, the current 9 rose vigorously in response to significant hyperglycemia over the last hour of the experiment, verifying the absence of electrode poisoning. [Figure 8]

[0031] Figure 8 is a diagram of an in-line filter that removes phenols from an insulin infusion line. A proximal supply insulin line 11 brings the insulin formulation from an insulin pump and connects to the proximal end of a filter 12. A protective membrane 13 prevents ingress of filter material into an insulin outlet line 14 located at the distal end of the filter. The close-up view in the right panel also shows a cylindrical retainer 15 that holds the protective membrane 13 and outlet line 14 securely to the distal end of the filter 12 without impeding the passage of insulin. [Figure 9]

[0032] Figure 9 (graph) demonstrates the effectiveness of the filter in removing phenols. Aspart insulin was placed at the proximal end of the filter. Multiple samples (0.25 mL each) were then collected (in 0.25 mL increments) during delivery of phosphate buffer. Assay results for insulin 16 (estimated by measuring total protein using a bicinchoninic acid [BCA] assay) are quantified on the left axis, and assay results for phenols 17 (using a nitroprusside-based assay) are quantified on the right axis. The filter material is Sephadex G10 (medium). Insulin passes through the filter very quickly after delivery, while phenols pass through very slowly, only after 3 mL has passed through the filter. [Figure 10]

[0033] Figure 10 shows the process in which microfabrication is used to create patterns for the electrodes and interconnect traces. After laminating titanium foil to polyimide, a layer of silver is sputtered onto the titanium, followed by a layer of photoresist. Portions of the photoresist are selectively removed to make the unwanted silver available for removal by an etchant 18. When the remainder of the photoresist is removed, the silver electrode pattern is revealed 19. A second coating of photoresist is applied, followed by platinum sputtering 20. When the photoresist is removed, the unwanted platinum is lifted, revealing the platinum electrode pattern 21. A next layer of photoresist is applied and selectively removed 22. In the absence of photoresist, the unwanted titanium can be etched away. Once the photoresist is removed 23, the correct titanium pattern is revealed 23. DETAILED DESCRIPTION OF THE INVENTION

[0024]

[0034] While various aspects of the present invention have been shown and described herein, it will be apparent to those skilled in the art that such aspects are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the aspects of the invention described herein may be employed.

[0025]

[0035] Whenever the term "at least," "greater than," or "greater than or equal to" appears before the first number in a series of two or more numbers, the term "at least," "greater than," or "greater than or equal to" applies to each of the numbers in that series. For example, 1, 2, or 3 or more is equivalent to 1 or more, 2 or more, or 3 or more.

[0026]

[0036] Whenever the term "not greater than," "less than," or "less than or equal to" appears before the first number in a series of two or more numbers, the term "not greater than," "less than," or "less than or equal to" applies to each of the numbers in the series. For example, 3, 2, or 1 or less is equivalent to 3 or less, 2 or less, or 1 or less.

[0027]

[0037] As used herein, the term "subject" generally refers to a person, individual, or patient. A subject may be a vertebrate, such as a mammal. Non-limiting examples of mammals include humans, apes, farm animals, sport animals, rodents, and pets. A subject may be a diabetic or a patient suspected of having diabetes. A subject may exhibit a symptom or symptoms indicative of a health or physiological condition or physical condition of the subject, such as diabetes. Alternatively, a subject may be asymptomatic with respect to such a health or physiological condition or physical condition.

[0028]

[0038] A valuable technology in the management of T1D is continuous glucose monitoring (GCM), in which a subcutaneously inserted sensor provides interstitial glucose data to the user every few minutes. For example, a JDRF-sponsored study may show that subjects of all ages who regularly use CGMs experience better glycemic control than non-users (e.g., as measured by hemoglobin A1C (A1C)). However, many subjects may find CGM use intrusive, and many may only use CGMs sporadically. Not surprisingly, CGM use may not translate to better glycemic control when used sporadically or infrequently.

[0029]

[0039] Daily life can be difficult for people who regularly use both an insulin pump and a CGM. Such individuals may need to carry two skin-penetrating devices, which may increase the risk of pain, infection, and other side effects compared to a single device. Individuals with T1D may carry multiple devices on their bodies, such as pumps and / or syringes, CGM receivers, vials of insulin, blood glucose monitors for calibrating the CGM, and blood glucose monitoring strips and lancets. Device multiplicity can lead to a situation known as "device burden," which can lead to frustration, anger, and a patient choosing between devices rather than utilizing all the devices that could improve their health.

[0030]

[0040] Recognizing the challenges encountered in clinical care and management due to issues related to device burden, the present disclosure addresses the unmet need for integrating a CGM and insulin pump cannula into a single device.

[0031]

[0041] Manufacturers' instructions may state that subcutaneous glucose sensors must be placed far from the insulin pump cannula site. Supporting this statement, during porcine studies, we found that current insulin formulations significantly interfere with currently available hydrogen peroxide-measuring sensors. More specifically, we found that preservatives in formulations, such as phenol and m-cresol, are electroactive and interfere with CGM.

[0032]

[0042] The present disclosure provides a device in which a glucose sensor can be successfully integrated with an insulin cannula, and methods for using the same. Such glucose sensors and insulin cannulas may be described, for example, by U.S. Patent No. 10,780,222, which disclosed osmium as a redox mediator element and pyridine- and imidazole-based ligands bound to osmium. The disclosed devices and methods can use alternative metals and alternative ligands, each of which can be used as a redox mediator.

[0033]

[0043] Rather than using separate insulin infusion catheters and CGM sensors, it may be desirable to create a single combined device. There are many different glucose sensing strategies that can be considered for such a combined sensing catheter. For example, optical sensing technology can be used for glucose. Optical glucose sensors can be constructed based on optical waveguides. Optical sensing methods can be based on glucose-binding fusion proteins. Fiber-optic sensors can have hollow fibers filled with glucose-binding assays. Porous hollow sensors can contain porous beads for optical determination of analyte concentration. Alternative sensing strategies, such as viscometry, can be used. However, all of these can face challenges when attempting to pair CGM with drug infusion (e.g., in a single device or in close proximity in a subcutaneous environment).

[0034]

[0044] A typical analyte sensor design may be based on amperometric principles, where an analyte is detected by generating an electrochemical signal related to the analyte of interest. Sensing electrodes may be fabricated through the use of sputtered or vapor-deposited thin films deposited on the surface of a support. In some embodiments, the indicator electrode (also called the working electrode) is made of platinum, gold, or carbon. When a positively biased indicator electrode is paired with a reference electrode, such as silver / silver chloride, redox-active analytes can be detected amperometrically. Adding an enzyme layer, such as glucose oxidase, can create a sensor specific for the analyte glucose. Glucose oxidase can convert glucose, which may not be easily detected amperometrically, to hydrogen peroxide, which can be easily detected (e.g., using a sensor). When a thin film of metal electrodes is deposited on an appropriate polymer thin film, such as polyimide, the resulting sensor may have the added advantage of flexibility. For example, users may find stiff catheters or needles uncomfortable or painful.

[0035]

[0045] A problem with electrodes made from thin metal films can be their brittleness; layers can delaminate when exposed to physical trauma such as impact, bending, shear stress, and tensile stress. For example, the durability of thin film electrodes can be limited.

[0036]

[0046] More specifically, numerous flexing cycles can lead to material failure (a phenomenon called cyclic fatigue). While the durability of thin films may be sufficient for short-term applications, longer-term indwelling sensing applications may require a much greater ability to withstand trauma. In the case of indwelling subcutaneous sensors, the sensor may be required to withstand repeated impacts and / or repeated flexing for periods lasting 3-7 days or longer. Metal thin films can crack, which can be exacerbated by immersion in moist, high-salinity environments such as those provided by mammalian blood or subcutaneous interstitial fluid. As a result, electrodes in commercially available CGM sensors (e.g., manufactured by Dexcom, Inc.) may be constructed from durable solid wires rather than thin films. Examples may include wire-based variable stiffness transdermal medical devices, wire-based transdermally implantable continuous analyte sensors with silicone-based membranes, biointerfaces for wire-based sensing electrodes, transdermal analyte sensor assemblies, flexible solid-state wire-based glucose sensors, multi-electrode wire-based sensors, and multilayer sensors with solid cores. However, wires or rods have a solid core and therefore may not be compatible with the delivery of drugs such as insulin, which may require a hollow lumen. These devices may face challenges in combined analyte sensing and drug delivery applications due to their lack of a hollow lumen.

[0037]

[0047] Other devices may use sensors coupled to hollow catheters (e.g., glucose sensors disposed within hollow catheters). More specifically, sensors may be placed inside larger diameter catheters placed within blood vessels. While such devices may be suitable for measuring fluid (e.g., blood) present within the catheter, such designs may not be suitable for sensing catheters for measuring glucose in subcutaneous adipose tissue. For use in subcutaneous tissue, the sensing element may need to be on the outer wall of the hollow catheter. In general, a "wire sensor within a tube" or "tube within a tube" design may not allow for proper function in subcutaneous tissue. For drug delivery, the lumen may need to be hollow. For example, consider a device designed to measure an analyte in the lumen, with a sensing element located inside the hollow portion. For an effective subcutaneous sensing catheter, it may be necessary to have an open interior (lumen) to enable drug delivery into the body. In one embodiment of the device of the present disclosure, the outer wall, which is not in contact with the drug and is bathed in glucose-containing subcutaneous interstitial fluid, is an appropriate location for the sensing element.

[0038]

[0048] Other sensor designs may require the withdrawal of a fluid sample from the body for sensing to occur. For example, hollow fiber-based glucose sensors may involve dialysis with a test fluid. As another example, hollow probes can be used to withdraw interstitial fluid. As another example, hollow electrochemical cells with internal sensing elements may require the withdrawal of a fluid sample. As another example, glucose dehydrogenase-based sensors may incorporate an interstitial fluid sampling device. As another example, a method for determining glucose concentration may require the use of a device with an external sensor coupled to a fluid sampling pump. As another example, a sensor may incorporate a hollow member and a lancet for interstitial fluid sampling. As another example, a system may incorporate a microdialysis-based sensor. As another example, a sampling device incorporates a vacuum to withdraw a blood sample from the skin surface. These devices may face challenges in applications that allow for ongoing drug delivery and simultaneous exposure of the sensor to interstitial fluid. As a result, these systems may not be compatible with continuous subcutaneous drug infusion.

[0039]

[0049] Other sensor designs can utilize microneedles to reduce the invasiveness of measurement techniques. However, microneedle arrays can face the challenge of keeping all of the microneedles in place in mammalian tissue during body movement. Because the microneedles are short in length, many of the needles may tend to come out of the tissue if a person makes a sudden or forceful movement. This problem of unintentional explantation may make them unsuitable for long-term use in outpatient settings.

[0040]

[0050] For example, a unified hollow structure can be used for analyte sensing and drug delivery. While insulin can be used, such a device may not be able to avoid oxidative interference from preservatives and the fragility of thin metal electrodes laminated to the hollow structure. Similarly, the device may not allow for glucose measurement in the presence of insulin preservatives and / or may not avoid the fragility of thin metal electrodes.

[0041]

[0051] To fabricate a combined sensor / catheter, biosensing elements can be incorporated into the wall of a hollow needle or catheter. For example, fabrication can involve depositing a metal (e.g., platinum, gold) thin-film indicator electrode and a thin-film silver (Ag / AgCl) reference electrode directly onto an underlying polymer layer, such as polyimide or polyester. One such design can incorporate printed electrode films. However, in vivo studies in animals have demonstrated significant problems with sensing catheters made with thin-film metal electrodes deposited onto a polymer layer. In particular, these sensors have exhibited frequent delamination and a general lack of durability.

[0042]

[0052] At many bias potentials, insulin preservatives (phenol and m-cresol) in the vicinity of a glucose-sensing indicator electrode create a large current (electron flow) that may not be easily distinguishable from high glucose levels. More specifically, when an indicator electrode in the presence of preservatives is polarized at a high bias potential, a large current may be present even in the absence of glucose. For this reason, a way to reduce or eliminate the glucose-like current is to use a much lower bias potential. When a hydrogen peroxide sensing system is utilized, it can be difficult to achieve a sufficient glucose current from peroxide oxidation while simultaneously minimizing interference from insulin preservatives.

[0043]

[0053] In contrast, when using certain systems, such as redox mediators (e.g., based on metals such as osmium, ruthenium, iridium, iron, and cobalt) that operate at low bias potentials, electrons can be transferred from glucose to the indicator electrode without interference from insulin preservatives. Examples of metal choices that can be used as mediators are disclosed herein. The mediator may be bound to a ligand, several options for which are disclosed herein. The mediator-ligand complex can be bound to a polymer, such as polyvinylpyridine or polyvinylimidazole, which can be further crosslinked with a bifunctional crosslinker and immobilized on the sensor surface.

[0044]

[0054] Instead of, or in conjunction with, the use of redox mediator chemistries, specialized filters can be used to capture phenol and m-cresol before delivery to a subject, thus preventing these compounds from reaching the subcutaneous space and causing interfering currents. Because these filters prevent phenol and m-cresol from reaching the subcutaneous space and reaching the amperometric sensor, such filters can be used in conjunction with sensors employing traditional hydrogen peroxide detection, such as platinum-based sensors that do not contain redox mediators.

[0045]

[0055] Regardless of whether a redox mediator or filter is utilized, if the layers of the sensing catheter are not durable, the device may not function properly. For example, if the thin metal films that make up the indicator electrodes are deposited directly on a polymer support, the thin electrode films may not be robust or durable. Instead, they may disintegrate and / or peel off from the polymer during use.

[0046]

[0056] To avoid this brittleness and at the same time minimize costs, it may be necessary to laminate the thin metal electrode film to an underlying metal such as titanium, which may need to be substantially thicker than the electrode film to be sufficiently robust.

[0047]

[0057] To reduce device burden, it may be desirable to be able to continuously measure glucose at the direct site of insulin delivery, particularly in subcutaneous interstitial fluid. In an attempt to better understand electrode or sensor response in the presence of insulin formulations, the experiment shown in Figure 1 was conducted. This figure shows the response of a platinum electrode (polarized at 600 mV versus an Ag / AgCl reference electrode) probed in phosphate-buffered saline (PBS). (For definition purposes, the term reference electrode in this disclosure refers to the reference electrode in a three-electrode system, or the combined reference + counter electrode or reference + auxiliary electrode in a two-electrode system.) The electrode was bare, i.e., not coated with an enzyme or outer membrane. Early in the experiment, hydrogen peroxide (HO) was added, and the electrode responded vigorously and maintained a steady current. At 13 minutes, a standard commercially available insulin formulation (Aspart Insulin, Novo Nordisk) was added to achieve a combined phenol and m-cresol (phenolic) concentration equal to 45 μg / mL. It is clear that a vigorous oxidative (rising) current was present immediately after the insulin formulation was administered. However, the increase in current was transient, and after a few minutes, it began to decrease despite the continued presence of phenols. At the 23 and 33 minute time points, more aspart insulin was administered, resulting in much higher concentrations of phenols, as shown. It is important to note that no increase in current was observed after these later additions; instead, the current continued to decrease, such that the final current was significantly lower than the original current obtained from HO (which also remained in solution). This progressive loss of current is due to poisoning of the electrode. More specifically, phenols and cresols undergo a process of electropolymerization, in which a thin layer of insulating polymer forms on the electrode surface. This layer is nearly impermeable to several analytes, including HO, and for this reason, after exposure to phenols, such electrodes are useless for measuring glucose or other analytes.

[0048]

[0058] Another experiment (not shown) was performed using preservative-free insulin (this preparation was purchased from Thermo Fisher Life Technologies under the brand name Gibco). This insulin did not undergo any electrochemical reaction and did not poison the electrode. This experiment demonstrates that the interference noted in Figure 1 is due to the preservative and not the insulin itself.

[0049]

[0059] We next investigated the effect of bias potential magnitude on the electrochemical response to phenol and cresol, as shown in Figure 2. In this experiment, a bare gold electrode was polarized at different potentials and sequentially exposed to phenol (10 mM) and m-cresol (10 mM). The electrode was exposed to the phenols for very short periods and washed between tests to remove any electropolymerized polymer. The results showed that the response to phenols was highly dependent on the bias potential magnitude. In particular, when the potential was increased to high potentials, e.g., above 350 mV, there was a very large oxidative reaction. In contrast, when the bias was decreased, the response was extremely low, especially below 250 mV.

[0050]

[0060] In an attempt to minimize interference by reducing the bias potential, we performed experiments using a redox-mediated chemical scheme. Similar results can be obtained by substituting other metals (e.g., ruthenium, iridium, iron, or cobalt) for osmium.

[0051]

[0061] Redox mediator complexes (e.g., based on metals such as osmium, ruthenium, iridium, iron, and cobalt) can be compounds suitable for accepting electrons from glucose oxidase, more specifically from the prosthetic group of glucose oxidase known as flavin adenine dinucleotide (FAD). The metal utilized as the redox mediator can be any member of the following redox mediator metal group: ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. Members of the redox mediator metal group can be abbreviated as MRMMG. Osmium can serve as a redox mediator; however, an advantage of the redox mediator metal group is that its members have substantially lower cost than osmium. In one embodiment, a member of the redox mediator metal group is coordinated to a ligand such as 4,4'-dimethyl-2,2'-bipyridine, which is also attached to the PVI polymer. Many other ligands can be used, some of which are disclosed herein. Binding to PVI can prevent the redox mediator ligand from dissociating from the polymer backbone.

[0052]

[0062] It should be understood that 4,4'-dimethyl-2,2'-bipyridine is just one example of a suitable ligand. Members of the ligand class include, but are not limited to: (1) Heterocyclic nitrogen compounds having one, two, three or four rings, such as pyridine or imidazole; (2) Ligands in which one or more pyridine rings are combined with one or more imidazole rings; (3) a ligand in which one or more non-nitrogen atoms are substituted in a heterocycle; and (4) Ligands in which other chemical groups are attached to heterocyclic ring atoms. These groups are often called "R" groups or pendant groups.

[0053]

[0063] Electron-donating groups such as methyl, methoxy, or amino, when bound to a member of the redox mediator metal family, can enable the member of the redox mediator metal family to transfer electrons at lower polarization biases. Members of the redox mediator metal family, along with members of the ligand class, can be referred to as redox mediators. For improved functionality, redox mediators can be bound to polymers, and this complex can be referred to as a redox mediator polymer (RMP). RMPs can be crosslinked with agents such as glutaraldehyde or polyethylene glycol diglycidyl ether, both of which link amine groups.

[0054]

[0064] In some embodiments, the RMP is deposited on a gold indicator electrode, although other materials, such as glassy carbon, graphite, platinum, or iridium, can also be used. The indicator electrode can also be made porous, for example, by using acid anodization, laser poration, or plasma etching.

[0055]

[0065] In some embodiments, the RMP is coated with a polymer layer called the outer membrane. This type of sensor does not require oxygen permeability to function, but does require some degree of glucose permeability. The outer membrane can be made of polyurethane, Nafion, poly(vinylpyridine), poly(vinylpyridine)-co-styrene, molecular weight cutoff polymer membranes, silicone, hydrogels, and many other materials that allow glucose permeation.

[0056]

[0066] For the exemplary experiments presented herein, we utilized members of the redox mediator metal group compounds shown in Figure 3. The polymer backbone 1 is composed of poly(1-vinylimidazole) (PVI). Two ligands, 4,4'-dimethyl,2,2'-bipyridine 2 and 3, are attached to redox mediator metal group member 4. Redox mediator metal group member 4 is attached to approximately one for every 5-15 imidazole groups on PVI.

[0057]

[0067] Using the RMP-based sensor and the conventional platinum H2O2-sensing sensor, we then performed the in vitro experiment shown in Figure 4. In this experiment, a gold sensor with RMP, glucose oxidase, and outer membrane coatings was compared to a platinum sensor coated with glucose oxidase and an outer membrane. The RMP-based sensor was biased at 180 mV, and the platinum sensor was biased at 600 mV. After initial exposure to a 5 mM glucose solution, platinum-based sensor 5 and RMP-based sensor 6 were then exposed to increasing amounts of a commercially available aspart insulin formulation (Novo Nordisk) containing phenols, as described for the earlier experiment shown in Figure 1. Figure 4 shows only the incremental response obtained at the highest concentration of phenols, 180 μg / ml. Each bar represents the results from one sensor. It should be noted that conventional platinum-based sensor 5 had a large negative response, while the RMP-based gold sensor had only a small positive response. As discussed earlier, this large negative response reduced the sensor's response to glucose (which remained in solution) to a point far below its original response, thus indicating some degree of electrode poisoning. As a follow-up to this experiment (not shown), both the platinum-based gold sensor and the RMP-based gold sensor were removed from the solution, rinsed, and re-exposed to 5 mM glucose. The platinum-based sensor had a very low, almost nonexistent response to glucose (verifying permanent poisoning), whereas the RMP-based sensor's response was vigorous and nearly identical to its original response to glucose. Substituting another metal (e.g., ruthenium, iridium, iron, or cobalt) for osmium may yield similar results.

[0058]

[0068] Figure 5 shows the response of an RMP-based sensor with a gold indicator electrode and an Ag / AgCl reference electrode to stepwise increases in glucose concentration in phosphate buffer during continuous argon sparging. In this case, the RMP and glucose oxidase were crosslinked with polyethylene glycol glycidyl ether, but similar results were obtained using glutaraldehyde liquid or glutaraldehyde vapor. Note that the response to glucose up to at least 25 mM is essentially linear.

[0059]

[0069] The preceding series of experiments demonstrates that a gold sensor coated with RMP and cross-linked glucose oxidase and polarized at 180 mV vs. Ag / AgCl can measure glucose with little or no interference from preservatives used in insulin formulations. In contrast, the use of a platinum sensor coated with cross-linked glucose oxidase and polarized at 600 mV undergoes an initial, very large oxidation current when exposed to phenols. Furthermore, if such exposure continues for more than a few minutes, the electrode is consistently poisoned by a dense layer of electropolymerized phenolic compounds, which prevents H2O2 and other common analytes from reaching the indicator electrode and being measured. Similar results can be obtained by substituting another metal (e.g., ruthenium, iridium, iron, or cobalt) for osmium.

[0060]

[0070] Subcutaneous devices are exposed to many types of trauma, for example, due to body movements and impacts typical of daily life. Thus, even if the chemical layer on the electrode successfully measures glucose without interference from phenols and cresols, a dual-use sensing catheter may not function accurately over its entire lifespan unless the catheter has a durable and robust construction.

[0061]

[0071] One approach to creating a continuous sensor integrated into the wall of an insulin infusion cannula is to laminate a flexible thin metal film onto the outer wall of a hollow tubular structure. However, if the material and process selection is not implemented correctly, the resulting electrode layer can be very brittle. More specifically, placing a thin metal electrode material (less than 100 nm thick) directly on top of a polymer surface (with or without a thin underlying adhesive layer such as Ti, Au, or Ni) results in a brittle device. The thin electrode film frequently peels off or disintegrates during impaction, making such devices unsuitable for use as catheters placed in the subcutaneous space for days. In fact, such designs can exhibit substantial electrode delamination after only a few hours of in vivo use. In our experience, whether or not a 25-200 nm tie (adhesion) layer is deposited underneath the electrode, such designs lead to frequent separation of the tie layer from the polyimide, frequent separation of the indicator or reference electrode thin film from the tie layer, and frequent fragmentation of the metal layer.

[0062]

[0072] On the other hand, placing a metal foil underneath a thin-film metal electrode significantly improves durability and fatigue resistance while maintaining sufficient flexibility for fabrication and use as a biosensor. The use of the term "foil" refers to a metal layer that is at least 2 micrometers (μm) thick, i.e., much thicker than the thin-film layers typically deposited by sputtering, evaporation, printing, or electroplating. Foils can have beneficial mechanical properties. For these reasons, metal foils (under thin electrode films) are well suited for durability purposes.

[0063]

[0073] All layers of a sensing catheter must be strongly bonded to adjacent layers. One method for creating an interface with good adhesion and good durability is to use a laminating press at high temperature and pressure. A high-tack adhesive, such as a B-stage acrylate, is placed at the interface of the foil and the underlying polymer, bonding the two materials together. After lamination, a thin-film electrode material can be deposited onto the durable metal foil. The metal foil is typically 2-15 μm thick.

[0064]

[0074] The metal that makes up the foil must be carefully selected. In the case of amperometric glucose sensors, the indicator electrode is typically platinum, gold, or carbon. Copper (commonly used as a foil for flexible electronic circuits) is not suitable for use in biosensors. Specifically, if interstitial fluid, copper, and platinum are in simultaneous physical contact, large galvanic currents can occur as a result of the joining of dissimilar metals. A suitable candidate for the foil is titanium, which we have found to be inexpensive and generates little to no galvanic current when paired with platinum. Silver and copper are not suitable materials for this foil. Gold is of intermediate value.

[0065]

[0075] Using the durable sensing catheter design discussed above, we conducted a series of studies in nondiabetic Yucatan minipigs weighing 33–60 kg. In preparation for this study, a sensing catheter was fabricated. A 12.5 μm-thick polyimide strip was laminated to a 5 μm-thick sheet of titanium foil. Three thin-film, 1 mm square platinum indicator electrodes and an Ag / AgCl reference electrode were sputtered onto the surface of the titanium foil. This electrode strip was wrapped and laminated to the exterior of a blunt, hollow, 21-gauge stainless steel tube using an epoxy adhesive designed for use in high-salinity, humid environments. The indicator electrode was coated with glucose oxidase and bovine serum albumin (BSA) in a 3:2 ratio, crosslinked with glutaraldehyde vapor, and then coated with a silicone-polyurethane copolymer outer membrane (Lubrizol, Inc.). The term used for such a dual-use device is a “glucose sensing catheter” or “sensing catheter.” A series of interconnecting traces originate from the three indicator electrodes and a single reference electrode and terminate in a body-worn electronic sensor module that is in electrical continuity with the sensing catheter. The sensor module contains a battery and a Bluetooth-enabled transceiver, which transmits the electrochemical signals to a personal computer or cell phone.

[0066]

[0076] Multiple sensing catheters attached to telemetry sensor modules were inserted into the subcutaneous tissue of the pig's abdomen under isoflurane anesthesia. The sensor modules were attached to the skin with cyanoacrylate adhesive, and each pig was then allowed to recover from anesthesia. The following morning, the animals were again anesthetized with isoflurane. After a stabilization period, a euglycemic clamp was performed for 5 hours. More specifically, to avoid hypoglycemia, an infusion of 20% glucose was given intravenously according to a computerized algorithm. At 105 minutes during the clamp, lispro insulin (a total dose of 0.22 units per kg, divided between two catheters for a total dose of 0.11 units per kg delivered through each catheter) was administered through some of the sensing catheters, as indicated by the arrows in Figure 6. No insulin was delivered through the other sensing catheters.

[0067]

[0077] Figure 6 shows average exemplary data obtained from several sensing catheters in which lispro insulin was delivered. The electrochemical sensor current 7 and blood glucose levels 8 (measured in duplicate by a Bayer Contour Next meter) are indicated by arrows. Note that immediately after insulin was administered, there was a very large current spike that rapidly decreased exponentially. Later in the experiment, at 300 minutes, a rapid infusion of 20% glucose was given intravenously, resulting in a significant increase in blood glucose levels to a level of approximately 300 mg / dL. It can be seen that the sensor was unable to respond strongly to this significant increase in glucose levels. During hyperglycemia, there was only a very small increase in current, which is typical of sensors that have undergone electrode poisoning. Many such experiments were performed in pigs. In summary, in approximately 40% of experiments in which lispro insulin was administered, there was a significant oxidative increase in current between 105 and 165 minutes, despite the fact that glucose was held constant. In these cases, it is likely that the insulin formulation flowed back onto the sensor element after exiting the catheter, causing an oxidative signal. Otherwise, it is believed that the insulin formulation flowed out of the catheter without contacting the sensing element and therefore did not cause an interfering signal. Similar results can be obtained by substituting other metals (e.g., ruthenium, iridium, iron, or cobalt) for osmium.

[0068]

[0078] Other porcine experiments were conducted using a sensing catheter with a gold indicator electrode and RMP coupled to glucose oxidase via glutaraldehyde. Figure 7 shows average data from several RMP-based gold sensors delivered with lispro insulin. Consistent with the in vitro data discussed above, there was little to no evidence of interference from insulin preservatives after the insulin formulation was administered. Sensor current 9 did not rise at 105 minutes when lispro insulin was administered. Furthermore, the RMP-based sensor responded strongly to significant hyperglycemia during the final hour of the study. Note the robust rise in blood glucose during the final hour of the study. During this rise, the robust increase in current 9 demonstrated the absence of electrode poisoning. Similar results can be obtained by substituting another metal (e.g., ruthenium, iridium, iron, or cobalt) for osmium.

[0069]

[0079] We have also discovered another approach to avoiding preservative-induced oxidation currents: the use of a filter placed in the insulin infusion line. For example, hydrophobic zeolite filtration can be used to remove insulin preservatives from vials of insulin formulation prior to injection. In one embodiment, we teach the use of an in-line filter designed for use by patients with diabetes who use portable insulin pumps to deliver insulin subcutaneously. Such a filter is depicted in Figure 8. The plastic tubing coming from the insulin pump 11 is attached to a filter cartridge 12 filled with a filter material. At the distal end of the filter cartridge is a protective membrane 13 that prevents filter beads or particles from being released into the insulin tubing (and thus into the patient's body). One such embodiment for this protective membrane is porous cellulose acetate, with a pore size smaller than the filter bead material. Many other membrane compositions and pore sizes are suitable for fabricating the protective membrane. Tube 14 carries the filtered insulin from the filter cartridge into the sensing catheter. The right panel of Figure 8 shows an enlarged view of the filter with additional details. Typically, it is necessary to utilize a retainer unit 15 that holds the filter cartridge 12, protective membrane 13, and outlet tube 14 securely in place. In some embodiments, it is also desirable to position the retainer unit at the proximal end of the filter.

[0070]

[0080] There are many such bead or particle materials that can be used to filter phenols from insulin formulations. Some of these materials include those typically used in size exclusion chromatography, also known as gel filtration chromatography and molecular sieve chromatography. As used herein, size exclusion media can be particles containing pores that trap smaller molecules and allow larger molecules to pass easily. In one embodiment, preservatives contained in insulin formulations, including m-cresol and phenol, are trapped within the small pores. Larger insulin molecules that are not trapped easily pass through the filter.

[0071]

[0081] One suitable filter material is cross-linked dextran, one brand of which is Sephadex®. Sephadex G10 is suitable because it is intended to separate compounds smaller than 700 daltons from those larger than 700 daltons. This grade of cross-linked dextran is suitable because cresols and phenols weigh approximately 100 daltons, while insulin and insulin analogs weigh approximately 5,800 daltons. Other grades of cross-linked dextran can also be used. In addition to dextran, other options for filter materials include carbon (including charcoal and activated carbon), alumina, silicates, silica, alumina and silica mixtures known as zeolites, and other compounds used to separate compounds based on molecular size. It is also possible to separate molecules based on hydrophobicity / hydrophilicity using materials typically used in reversed-phase high-performance liquid chromatography. Phenol and cresol are more hydrophobic than insulin.

[0072]

[0082] Figure 9 shows the results of an experiment conducted to separate aspart insulin from its preservative. Sephadex medium G10 beads, 40-120 μm (GE Healthcare, Inc.), were used to fabricate a filter similar to that shown in Figure 8. A column measuring 3 mm in diameter and 64 mm in length was loaded with 10 units of aspart insulin. Then, 0.25 mL of PBS was delivered by an insulin pump every 5 minutes, and an equal volume of eluate was collected every 5 minutes. The eluate was repeatedly assayed for insulin using a BCA total protein assay (trace 16). Phenol was repeatedly assayed using a nitroprusside-based assay with a spectrophotometric endpoint (trace 17). The results show that insulin elutes very early in the experiment, with little to no insulin eluting after the second collection. In contrast, phenol does not elute until later in the experiment, after 3 mL had been collected. These results demonstrate that this embodiment works well for individuals with diabetes who use insulin pumps. The insulin reservoirs on currently available pumps hold up to 3 mL of insulin formulation, so for pump users using such filters, phenols may not appear during the 3-day use period during which no more than 3 mL of insulin formulation can be administered.

[0073]

[0083] A variation on the use of filter materials is to electrically connect them and electrochemically remove interfering substances. As an example, activated carbon filter particles packed and immersed in saline solution are conductive; therefore, the carbon can be used as an indicator electrode, polarized by a power supply at 400–800 mV relative to a suitable reference electrode, such as an Ag / AgCl electrode. In such cases, to avoid short circuits, the reference electrode cannot contact the carbon, and a sheath can surround the reference electrode. The sheath prevents contact with the carbon, allowing the saline to complete the anode-cathode circuit by allowing electrons to flow. When properly biased, the carbon oxidizes and electropolymerizes phenol and m-cresol rather than allowing them to pass through the filter. In such filters, some of the phenols can be adsorbed onto the carbon normally, while other phenols are simultaneously electropolymerized into a thin layer of plastic that remains on the carbon in the disposable filter. The use of electropolymerization and adsorption is more efficient than adsorption alone.

[0074]

[0084] It is important to note that there are many physical forms that a filter can take other than the single long tubular structure shown in Figure 8. For example, the filter could loop back on itself multiple times in a serpentine fashion. Such a design would not occupy as much longitudinal distance.

[0075]

[0085] For use in people with diabetes, the filter can be placed anywhere in the insulin delivery line, for example in the insulin reservoir (which is usually located with the pump body), in the insulin tubing, or in the insulin fluid pathway in the skin-worn sensor module just proximal to the entrance of the fluid into the sensing catheter.

[0076]

[0086] When filters are used, a higher polarization potential bias can be used so that the sensing system can utilize standard sensing of hydrogen peroxide. In such cases, a redox mediator is not required. A high bias, typically greater than 500 mV, is used to optimize the signal from the oxidation of hydrogen peroxide. Alternatively, filters can be used in combination with a redox mediator system with a lower bias. Such a combination has the advantage of using two effective methods to significantly reduce the adverse effects of phenols and cresols during CGM.

[0077]

[0087] The above description teaches the use of a filter to remove phenols from the insulin delivery line after the insulin formulation is placed in the pump reservoir but before the insulin is pumped into the dual-use sensing catheter. However, it should be noted that such a filter can also be used in a standard insulin infusion set (without a glucose sensor). It is important to note that phenol and m-cresol have many toxic effects. These compounds have been linked to cancer, particularly bladder cancer. The U.S. Environmental Protection Agency has classified m-cresol as a Category C (probable human carcinogen), citing a link between phenol administration and weight loss and neurotoxicity. Additionally, these compounds have been associated with many other adverse effects, including inflammation at the site of insulin administration. More recently, phenols have been clearly shown to be cytotoxic to mammalian cells.

[0078]

[0088] For these reasons, many people who take insulin may decide that they do not want to be exposed to the high concentrations of phenols that are present in all formulations of insulin intended for human use. Thus, even in the absence of a sensing catheter, an insulin infusion set with a phenols filter is a useful device applicable to people who use infusion pumps. For people who do not use insulin pumps, the same filtering material can be used to remove phenols from commercially available insulin formulations before administering the drug by injection. [Example]

[0079]

[0089] Example 1: Redox mediator-based sensing catheter

[0090] Laminating a metal foil to a polymer support

[0091] Objective: This process produces a titanium and polyimide laminate (Ti / Pi). In this example, the Ti is 5 μm thick and the polyimide is 12.5 μm thick, but these dimensions should not be construed as limiting. This example produces a laminate rectangle measuring 60 mm x 85 mm.

[0080]

[0092] Materials include deionized water; polyimide sheet with B-stage acrylate adhesive; titanium foil; press pad; Teflon sheet and graphite press plate; and a heated hydraulic press capable of achieving 400°F.

[0081]

[0093] Plate setting process: Between the call (pressure applying) plates of the hydraulic press, the materials should be stacked from bottom to top in the following order: graphite press plate; press pad; titanium foil; polyimide (with B-stage adhesive facing the titanium foil); press pad; graphite press plate.

[0082]

[0094] Before working with polyimide and titanium, prepare graphite plates, graphite foil, and Teflon sheets. All sheets should be cut to the size of the graphite plates, cleaned with isopropyl alcohol (IPA), and then carefully inspected for lint or contaminants.

[0083]

[0095] To operate the press: Place the plate stack in a hydraulic press and apply 5000 lb of force to the coal plates. Set the temperature settings to 375°F for both the top and bottom plates. Once both coal plates reach 375°F, set the press to 15000 lb and let it sit for 1 hour. Allow the coal plates to cool to below 100°F, then remove the plate stack from the press.

[0084]

[0096] General equipment and supplies (for all steps below): double-sided polyimide tape; plastic cards; razor blade; 50x75mm glass slides; isopropyl alcohol (IPA); deionized (DI) water; Pt (platinum) target; Ag (silver) target; aluminum foil; Ar (argon) plasma etcher; quartz crystal microbalance (QCM); sputtering tool; hot plate; mask aligner, e.g., OAI 200 benchtop mask aligner; spin coater capable of 300 rpm; argon source.

[0085]

[0097] Preparing Ti / PI laminates for application of gold and Ag electrodes

[0098] Clean the glass slide with soap and tap water, wash with IPA, rinse with deionized water, and Ar plasma clean for 1 minute; allow to dry. Place double-sided polyimide tape on a hot plate. Apply polyimide tape and remove any air bubbles. Place aluminum foil on the hot plate; apply double-sided polyimide to the slide and place the rigid backer adhesive side up. Apply Ti foil to the rigid backer. Apply Ti / polyimide + rigid backer to the polyimide tape. The stacking order should be (bottom to top): glass slide, double-sided polyimide tape, rigid backer, Ti / polyimide laminate (Ti side up).

[0086]

[0099] Silver film deposition

[0100] Objective: To deposit a layer of Ag (later chlorinated to Ag / AgCl) to fabricate a reference electrode. The nominal thickness is 400 nm to allow for a reasonable thickness of Ag / AgCl after chlorination (chlorination reduces the Ag thickness). In this process, sputtering of silver is used, but other methods, such as thermal evaporation, printing, or electroplating, can also be used. Required materials include: a treated 50 x 75 mm Ti / PI sheet on a glass slide, a sputtering unit, e.g., CRC-100, an Ag target, and Ar compressed gas.

[0087]

[0101] To sputter the Ag layer, place the substrate in the sputtering unit and use a vacuum pump to remove any exposed adhesive. The sputtering chamber is filled with Ar, and the operator equilibrates the system to 7 mTorr. Sputter until the quartz crystal microbalance (QCM) reads 5.00 kA (500 nm) for Ag (Gain = 75, Density = 10.5, Z Ratio = 0.529, Tooling Factor = 256). Remove the device from the sputtering unit. A tape test with 3M Magic Scotch tape in a corner confirms good adhesion. Store in a dust-free, covered container.

[0088]

[0102] Ag patterning and etching (removing unwanted Ag).

[0103] See Figure 10 for a diagram of the main microfabrication (electrode patterning) steps. Objective: To pattern photoresist for Ag pads on Ti / PI supports. Materials: 50 x 75 mm silver-sputtered Ti / PI substrates on glass slides; NaOH pellets; 300 mL beaker; 250 mL beaker; optical mask, S1813 (photoresist); 80 / 20 primer (80% propylene glycol monomethyl ether acetate and 20% hexamethyldisilazane (HMDS) primer). Materials for cleanroom use include mask aligner; spinner; hot plate; deionized water; scale; S1800 series photoresist; NaOH (pellets or solution).

[0089]

[0104] First, perform the general photoresist process included below. Then, mix the Ag etching solution. Add 75 mL of 3% USP grade H2O2, followed by 8 mL of 30% laboratory grade ammonium hydroxide to the crystallization dish. Immerse the patterned substrate in the solution for 30 seconds and gently agitate. If the reaction is complete, no bubbles may form. Rinse with deionized water and blow dry with nitrogen gas or argon. Remove the photoresist with 0.3 M NaOH solution.

[0090]

[0105] AU patterning, sputtering and lift-off

[0106] Objective: To pattern Au pads on Ti / PI / Ag supports. Materials included: 50 x 75 mm silver-sputtered Ti / PI supports on glass slides; NaOH pellets; 300 mL beaker; 250 mL beaker; optical mask; S1813 primer; Ti / PI / glass with Ag deposited on its surface; 80 / 20 primer as detailed above; Ag-etched thin film mask; 3 mL pipette; acetone; isopropyl alcohol (IPA); crystallization dish; graduated cylinder; and timer.

[0091]

[0107] Perform the general photoresist process, including: Rinse under Ar for 1 minute; Turn on the vacuum system; Sputter 90 nm (0.900 K) of Pt; Sputter 50-90 nm of Au (density = 19.3, Z ratio = 0.381); Completely cover the substrate using Scotch tape; Press firmly across the substrate, then slowly remove to remove the Au layer; Examine the tape test sheet for any failure of the Au adhesion; Use additional tape pieces to remove any bridges between the Au pads; Remove the photoresist / residual Pt / Au using the tape method (cover the entire array with 3 m of Velcro®), then sonicate in 0.5 M NaOH. If any bridges remain, gently scrub them off using Kimwipes while still in the solution.

[0092]

[0108] Titanium etching (removing unwanted Ti to create electrical interconnects)

[0109] Purpose: To define and separate the titanium traces on the sensor. It is important to prevent the titanium underneath the indicator electrode or indicator electrode interconnect trace from contacting the titanium underneath other indicator electrodes / traces or the titanium underneath the reference electrode / trace. Materials include: Ti / Pi mounting slide; titanium etchant; 400 mL beaker; crystallization dish; deionized water; NaOH; and ultrasonic cleaner.

[0093]

[0110] A typical photoresist process is carried out which includes: Prepare the etchant bath Place the substrate in the etching solution, observe carefully, and rinse with deionized water once etching is complete.

[0094]

[0111] Rinse with deionized water and blow dry with nitrogen or argon.

[0112] Prepare sensors for human use: individualize, wrap, chlorinate, apply a protective coating to the reference electrode, and clean the indicator electrode

[0113] Mechanical or photonic techniques, such as a UV laser (wavelength: 405 nm), are used to individualize each of the three electrode strips.

[0095]

[0114] The electrode strip is wrapped around a 21-25 gauge stainless steel needle (with a sharp bevel at the end) or blunt tubing. The electrode strip is wrapped axially around the needle / tubing and glued using epoxy or other biocompatible adhesive. When using blunt tubing, a sharp stylet within the tubing is utilized to pierce the skin during insertion (this stylet is later removed, allowing drug delivery through the lumen of the tubing).

[0096]

[0115] Ferric chloridize with 50 mM FeCl3 for 5-10 minutes. Alternative: Electrochloridize at 0.6 V for 10 minutes using a power supply designed for Ag as the anode (+) and Pt as the cathode (-). The bath for electrochlorination is KCl and HCl, both 0.5 M.

[0097]

[0116] Voltage cycle the indicator electrode in 1x PBS at -1.5 volts for 5 minutes, 1.5 volts for 5 minutes, and -1.5 volts for 5 minutes (wash). Check for the presence of air bubbles at the electrode site.

[0098]

[0117] A redox mediator polymer and glucose oxidase are applied to the surface of a gold indicator electrode. In this example, the redox mediator polymer listed is poly-(1-vinyl)-imidazole-MRMMG-4,4'-dimethyl-2,2'-bipyridine. However, there are other compounds that can be used with either pyridine- or imidazole-based MRMMG ligands, with polyvinylpyridine, polyvinylimidazole, or other polymers as the backbone. Similar results can be obtained using other metals (e.g., ruthenium, iridium, iron, or cobalt) instead of osmium.

[0099]

[0118] Before starting this process, three gold electrodes are wrapped, cleaned, and chlorinated.

[0119] Using deionized water as the solvent, prepare 1 mL of each of the following solutions: redox mediator polymer (10 mg / mL) and glucose oxidase, 100 units / mL (10 mg / mL). Combine 40 μL of redox mediator solution and 10 μL of glucose oxidase solution. For manual dispensing, draw up this mixture into a 1 mL plastic syringe with a 30-gauge needle, carefully place the tip of the needle in the center of each of the three electrodes, and then dispense a small drop (1 μL) onto each electrode without coating the reference electrode. After partial drying, a second layer of the mixture can be applied. Alternatively, a microdispensing device such as an inkjet printer can be used, taking care not to heat the enzyme above 50°C.

[0100]

[0120] The holder is placed upright in a glutaraldehyde vapor chamber (25% glutaraldehyde) for 30 minutes and then allowed to cure at room temperature for 30 minutes.

[0121] The outer membrane deposited over the entire shaft, including the indicator and reference electrodes, can be one of many glucose-permeable polymers, including polyurethane, silicone, composite silicone-polyurethane, or other polymers. One effective outer membrane is poly-(4-vinyl or 2-vinyl)pyridine-co-styrene (10-30% styrene, PVP-S), 64 mg / ml in absolute ethanol. This polymer can be deposited manually, using an automated dip coater, with an inkjet printer, microcontact printing, or other precise dispensing methods. Coat the entire sensor shaft with the outer membrane material. Allow to dry at room temperature for 15 minutes.

[0101]

[0122] After drying, the sensor can be tested in solutions of glucose, interfering compounds, etc.

[0123] Assemble into an electronic module that serves the purpose of telemetry and polarization bias application

[0124] The sensing catheter is inserted into a battery-powered telemetry module (eg, a low-energy Bluetooth module such as that sold by Nordic, Inc.).

[0102]

[0125] For the redox mediator polymer approach discussed above, a potential bias of 180 mV is appropriate. Such a low bias largely avoids signal artifacts due to oxidation of insulin preservatives (phenol, m-cresol) that would be seen if a higher bias were used. The low bias also avoids the electropolymerization problem routinely seen with the use of higher bias potentials. When a larger bias potential is used, the cresol and / or phenol undergo a process of electropolymerization, which deposits a cohesive, thin layer of insulating plastic on the electrode. This plastic layer reduces or eliminates the ability of members of the redox mediator metal group to communicate with the electrode material and also reduces the transport of molecules such as hydrogen peroxide to the surface of the indicator electrode.

[0103]

[0126] sterile

[0127] Exposure to electron beam, gamma irradiation, ethylene oxide or activated glutaraldehyde sterilization solutions.

[0104]

[0128] Attach to insulin pump and operate the device

[0129] After priming with insulin, an infusion line from an insulin pump (e.g., Medtronic Minimed, Animas Ping, Tandem t-slim, Roche Spirit, etc.) is attached to the sensing catheter (located in the subcutaneous tissue) and insulin is delivered. A constant pressure head from the fluid infusion line prevents fluid from backflowing out of the body. Glucose concentration or current or voltage data representing glucose concentration is obtained from the sensor for display to the user. These data are transmitted via Bluetooth or other wireless protocols to the insulin pump's display, a computer, a dedicated medical device, or a mobile phone. Data storage can be performed in any of these devices or in a body-worn electronics unit that interfaces directly with the subcutaneous sensing catheter. An advantage of storing glucose data in the body-worn unit is that data is not lost if the receiving unit is lost or goes out of range.

[0105]

[0130] General photoresist process (common to multiple processes)

[0131] Materials: 50 x 75 mm Ti / PI support on glass slide; NaOH pellets or solution; 300 mL beaker; 250 mL beaker; optical mask; photoresist; 80 / 20 primer as defined above.

[0106]

[0132] Method: Mix 200ml of 0.1M NaOH (8g / L in pellets, or 15mL / L in a 10M solution) primary developer in a glass dish. Ensure solution is well mixed, especially if using NaOH pellets. Mix 0.075M NaOH secondary rinse in a glass dish. Ensure solution is well mixed. Spin coat 3mL of 80 / 20 primer using standard method - 1000RM for 10 seconds, followed by 3000RM for 30 seconds. Bake at 85°C for 3 minutes. Spin coat 3 layers of photoresist using standard method. Bake substrate at 85°C for 1 minute between each spin step. Expose at 600W for 180 seconds. Bake for a further 60 seconds. Develop in 0.1M NaOH developer with gentle agitation. Rinse in secondary bath for 10 seconds. Dry with nitrogen gas and examine remaining resist for developed areas. (The exposed areas should appear uniform across the substrate. Properly cleaned areas may acquire a faint white appearance as they transition from wet to try if no photoresist remains on the surface.) Bake for 10 minutes and allow to cool. If areas remain, dip in the primary and secondary baths for an additional 5 seconds and check again. If significant areas remain, air dry, rinse with 0.3M NaOH, and return to step 4. Check process parameters.

[0107]

[0133] Example 2: Filtration using a platinum indicator electrode with a high bias potential

[0134] Many aspects of this example are the same as Example 1. However, instead of Au being deposited, Pt is deposited by sputtering, using these sputter settings: density=10.5 and Z ratio=0.529.

[0108]

[0135] No redox mediator is used. Glucose oxidase is applied with bovine serum albumin as a protein extender. A glutaraldehyde crosslinker is used to link the amine groups of glucose oxidase and albumin, with a weight ratio of glucose oxidase:albumin:liquid glutaraldehyde ranging from 6:4:5 to 6:4:1. The mixture applied to the Pt electrode is allowed to dry at 40°C for at least 10 minutes. Additional layers can be deposited to increase glucose sensitivity. In such cases, the final coating is allowed to dry for at least 20 minutes. It is then rinsed in agitated deionized water for 10-15 minutes to remove unbound enzyme. An outer membrane coating consisting of 1.5-2.5% w / v polyurethane (PU) or a copolymer of silicone and polyurethane is deposited twice on the indicator electrode(s) and reference electrode(s). Commercial manufacturers such as AdvanSource Biomaterials, Lubrizol, or DSM Polymers manufacture such polymers. The silicone fraction is used to control oxygen permeation; polyethylene oxide or polyethylene glycol moieties or other polar moieties are used to control glucose permeation. A suitable solvent is a mixture of THF and DMAC (25:75, V / V). Each PU coating is dried at 40°C for 20 minutes. The solvent and polymer / solvent mixture are kept dry with molecular sieves 3A or 4A.

[0109]

[0136] A suitable material for the filter is Sephadex G10, which is rated to separate compounds with molecular weights greater than 700 Da from those less than 700 Da. A suitable tubular structure with an internal diameter of approximately 3 mm and an internal length of at least 64 mm is packed with Sephadex medium G10 beads measuring 40 to 120 μm. The filter is placed in the insulin formulation fluid pathway. The distal end of the filter is surrounded by a porous cellulose acetate membrane to prevent Sephadex gel from entering the fluid pathway and being delivered to the patient. The pore size of the cellulose acetate is 0.22 μm. Prior to adding the insulin formulation to the filter, the filter beads are ideally exposed to an aqueous buffer, such as phosphate buffer, to swell the beads.

[0110]

[0137] While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. It is not intended that the present invention be limited by the specific examples provided herein. While the present invention has been described with reference to the foregoing specification, the descriptions and illustrations of the embodiments herein are not intended to be construed in a limiting sense. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Furthermore, it is to be understood that all aspects of the present invention are not limited to the specific depictions, configurations, or relative proportions set forth herein, which depend upon a variety of conditions and variables. It should be understood that various alternatives to the embodiments of the present invention described herein may be employed in practicing the invention. Accordingly, it is intended that the present invention cover any and all such alternatives, modifications, variations, or equivalents. It is intended that the following claims define the scope of the invention, and that methods and structures within the scope of these claims and their equivalents be covered thereby. This specification includes the disclosure of the following inventions. [Item 1] A device for delivery of insulin or insulin analog formulations and measurement of subcutaneous glucose concentrations, comprising: a hollow tube comprising a proximal end and a distal end, the proximal end in fluid communication with a source of insulin or an insulin analog formulation, the distal end designed to subcutaneously deliver the insulin or insulin analog formulation, the insulin or insulin analog formulation comprising an excipient comprising phenol or cresol; and an amperometric glucose sensor positioned no more than a predetermined distance from the distal end, the amperometric glucose sensor comprising: an electrode layer comprising at least one indicator electrode, the electrode layer underlying a redox catalyst layer comprising (1) a redox mediator comprising a metal compound covalently bound to a ligand and (2) an enzyme comprising glucose oxidase or glucose dehydrogenase; Devices containing: [Item 2] The device according to item 1, further comprising a housing having an upper accessible surface and a lower surface designed to be attached to the skin surface. [Item 3] The device of item 1, wherein the amperometric glucose sensor is disposed on a second hollow tube including a second distal end, the second distal end being designed to be inserted subcutaneously. [Item 4] The device according to item 1, wherein the at least one indicator electrode comprises gold, carbon, graphite, platinum, or iridium. [Item 5] The device according to item 1, wherein the ligand is pyridine-based. [Item 6] The device according to item 5, wherein the ligand is 4,4'-dimethyl-2,2'-bipyridine. [Item 7] The device according to item 1, wherein the ligand is imidazole-based. [Item 8] The device according to item 1, wherein the redox mediator is bound to poly(4-vinylpyridine). [Item 9] The device according to item 1, wherein the redox mediator is bound to poly(1-vinylimidazole). [Item 10] The device according to item 1, wherein the excipient comprises phenol. [Item 11] The device according to item 1, wherein the excipient comprises cresol. [Item 12] The device described in Item 1, wherein the predetermined distance is approximately 15 millimeters (mm), 14 mm, 13 mm, 12 mm, 10 mm, 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, or 1 mm. [Item 13] The device according to item 1, wherein the amperometric sensor further comprises a reference electrode. [Item 14] The device according to item 13, wherein the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. [Item 15] The device according to item 1, wherein the amperometric sensor further comprises an insulating layer and a metal layer, the insulating layer being bonded to the metal layer, and the metal layer being bonded to the electrode layer. [Item 16] The device according to item 15, wherein the insulating layer comprises a polyimide or a liquid crystal polymer. [Item 17] The device according to item 15, wherein the metal layer has a thickness of at least about 1 micrometer (μm), 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. [Item 18] The device according to item 17, wherein the metal layer comprises titanium, gold, or platinum. [Item 19] The device of item 1, wherein the electrode layer comprises a thin film having a thickness not exceeding about 1000 nanometers (nm), 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm. [Item 20] The device of item 1, wherein the redox mediator and the enzyme enable electron transfer from subcutaneous glucose to the at least one indicator electrode sufficient to cause the amperometric glucose sensor to respond to subcutaneous glucose concentrations at an applied bias potential not exceeding about +250 millivolts (mV), +200 mV, +150 mV, +100 mV, or +50 mV relative to a reference electrode. 21. The device of claim 20, wherein the applied bias potential of no more than about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV relative to the reference electrode prevents the electrode layer from substantially undergoing electropolymerization of the excipients during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining the sensitivity of the amperometric glucose sensor to subcutaneous glucose concentrations in the presence of the insulin or insulin analog formulation. [Item 22] The device according to any one of Items 1 to 21, wherein the metal compound contains a metal selected from the group consisting of osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. [Item 23] The device according to Item 22, wherein the metal compound comprises a metal selected from the group consisting of ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. [Item 24] The device according to any one of items 1 to 23, wherein the ligand comprises a heterocyclic nitrogen compound, a pyridine ring combined with an imidazole ring, a non-nitrogen element substituted in the heterocyclic ring, or a pendant "R" group attached to the heterocyclic ring. [Item 25] The device according to Item 24, wherein the heterocyclic nitrogen compound comprises a pyridine or imidazole having one, two, three or four rings. [Item 26] For delivering insulin or insulin analogue formulations and measuring subcutaneous glucose concentrations 1. A method for producing a medicament for use in a pharmaceutical composition comprising the steps of: (a) providing a device for delivery of insulin or an insulin analog formulation and measurement of subcutaneous glucose concentrations, said device comprising: (i) a hollow tube comprising a proximal end and a distal end, wherein the proximal end is in fluid communication with a source of insulin or an insulin analog formulation, and the distal end is designed to subcutaneously deliver the insulin or insulin analog formulation, wherein the insulin or insulin analog formulation comprises an excipient comprising phenol or cresol; and (ii) an amperometric glucose sensor positioned no more than a predetermined distance from the distal end, wherein the amperometric glucose sensor comprises: an electrode layer comprising at least one indicator electrode, wherein the electrode layer underlies a redox catalyst layer comprising (1) a redox mediator comprising a metal compound covalently bound to a ligand and (2) an enzyme comprising glucose oxidase or glucose dehydrogenase; (b) connecting the proximal end of the hollow tube to a source of the insulin or insulin analog formulation; (c) performing subcutaneous insertion of the distal end of the hollow tube into the subject; and (d) simultaneously (1) delivering the insulin or insulin analog formulation subcutaneously to the subject, and (2) measuring the subcutaneous glucose concentration of the subject; A method comprising: [Item 27] ​​The method described in Item 26, wherein the device further comprises a housing having an upper accessible surface and a lower surface, and the method further comprises attaching the lower surface to the skin surface of the subject. [Item 28] The method described in Item 26, wherein the amperometric glucose sensor is disposed on a second hollow tube including a second distal end, the second distal end being designed to be inserted subcutaneously. [Item 29] The method according to Item 26, wherein the at least one indicator electrode comprises gold, carbon, graphite, platinum, or iridium. [Item 30] The method according to Item 26, wherein the ligand is pyridine-based. [Item 31] The method according to Item 30, wherein the ligand is 4,4'-dimethyl-2,2'-bipyridine. [Item 32] The method according to Item 26, wherein the ligand is imidazole-based. [Item 33] The method according to Item 26, wherein the redox mediator is bound to poly(4-vinylpyridine). [Item 34] The method according to Item 26, wherein the redox mediator is bound to poly(1-vinylimidazole). [Item 35] The method according to Item 26, wherein the excipient comprises the phenol. [Item 36] The method according to Item 26, wherein the excipient comprises cresol. [Item 37] The method according to Item 26, wherein the predetermined distance is about 15 millimeters (mm), 14 mm, 13 mm, 12 mm, 10 mm, 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, mm, 5mm, 4mm, 3mm, 2mm or 1mm. [Item 38] The method according to Item 26, wherein the amperometric sensor further comprises a reference electrode. [Item 39] The method according to Item 38, wherein the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. [Item 40] The method according to Item 26, wherein the amperometric sensor further comprises an insulating layer and a metal layer, the insulating layer being bonded to the metal layer, and the metal layer being bonded to the electrode layer. [Item 41] The method according to Item 40, wherein the insulating layer comprises a polyimide or a liquid crystal polymer. [Item 42] The method according to Item 40, wherein the metal layer has a thickness of at least about 1 micrometer (μm), 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm. [Item 43] The method according to item 42, wherein the metal layer comprises titanium, gold, or platinum. [Item 44] The method according to Item 26, wherein the electrode layer comprises a thin film having a thickness not exceeding about 1000 nanometers (nm), 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm. [Item 45] The method described in Item 26, further comprising applying a bias potential of no more than about +250 millivolts (mV), +200 mV, +150 mV, +100 mV, or +50 mV relative to a reference electrode, wherein the redox mediator and the enzyme enable sufficient electron transfer from subcutaneous glucose to at least one indicator electrode to cause the amperometric glucose sensor to respond to subcutaneous glucose concentration at the applied bias potential. [Item 46] The method of item 45, wherein the applied bias potential prevents the electrode layer from substantially undergoing electropolymerization of the excipients during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining the sensitivity of the amperometric glucose sensor to the subcutaneous glucose concentration in the presence of the insulin or insulin analog formulation. [Item 47] The method according to any one of Items 26 to 46, wherein the metal compound contains a metal selected from the group consisting of osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper. [Item 48] The method according to Item 47, wherein the metal compound comprises a metal selected from the group consisting of ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron and copper. [Item 49] The method according to any one of Items 26 to 48, wherein the ligand comprises a heterocyclic nitrogen compound, a pyridine ring combined with an imidazole ring, a non-nitrogen element substituted in the heterocyclic ring, or a pendant "R" group attached to the heterocyclic ring. [Item 50] The method according to Item 49, wherein the heterocyclic nitrogen compound comprises a pyridine or imidazole having one, two, three or four rings. [Item 51] The method according to any one of Items 26 to 50, wherein the subject has type 1 diabetes. [Explanation of symbols]

[0111] 1 polymer repeat unit 2 4,4'-dimethyl, 2,2'-bipyridine moiety 3 4,4'-dimethyl, 2,2'-bipyridine moiety 4. Redox mediator metal group 5 Current density 6 Gold Sensor 7 Current measurement signal 8. Glucose Levels 9 Current measurement signal 10. Glucose Levels 11 Proximal supply insulin line 12 filters 13 Protective film 14 Insulin outlet line 15 Cylindrical cage 16. Insulin 17 Phenol 18 Photoresist 19 Silver electrode pattern 20 Shirokane 21 Platinum electrode pattern 22 Photoresist 23 Correct titanium pattern

Claims

1. 1. A device for the delivery of insulin or insulin analogue formulations and measurement of subcutaneous glucose concentrations, comprising: a hollow tube comprising a proximal end and a distal end, the proximal end in fluid communication with a source of insulin or an insulin analog formulation, the distal end designed to subcutaneously deliver the insulin or insulin analog formulation, the insulin or insulin analog formulation comprising an excipient comprising phenol or cresol; and an amperometric glucose sensor positioned no more than a predetermined distance from the distal end, the amperometric glucose sensor comprising: an electrode layer including at least one indicator electrode, (1) a redox mediator comprising a metal compound covalently bound to a pyridine-based or imidazole-based ligand, wherein the metal compound comprises a metal selected from the group consisting of ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper; and (2) Enzymes containing glucose oxidase or glucose dehydrogenase an electrode layer underlying a redox catalyst layer comprising the redox mediator and enzyme enable sufficient electron transfer from subcutaneous glucose to at least one indicator electrode to cause the amperometric glucose sensor to respond to subcutaneous glucose concentrations at an applied bias potential not exceeding +250 millivolts (mV) relative to the reference electrode; an applied bias potential of no more than +250 mV relative to the reference electrode allows the electrode layer to be substantially free from electrochemical reaction of the excipients during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining the sensitivity of the amperometric glucose sensor to subcutaneous glucose concentrations in the presence of insulin or insulin analog formulations; Devices containing:

2. 10. The device of claim 1, further comprising a housing including an upper accessible surface and a lower surface designed to be attached to a skin surface.

3. 10. The device of claim 1, wherein the amperometric glucose sensor is disposed on a second hollow tube including a second distal end, the second distal end being designed to be inserted subcutaneously.

4. 10. The device of claim 1, wherein the at least one indicator electrode comprises gold, carbon, graphite, platinum, or iridium.

5. 10. The device of claim 1, wherein the ligand is pyridine-based.

6. 6. The device of claim 5, wherein the ligand is 4,4'-dimethyl-2,2'-bipyridine.

7. 10. The device of claim 1, wherein the ligand is imidazole-based.

8. 10. The device of claim 1, wherein the redox mediator is bound to poly(4-vinylpyridine).

9. 10. The device of claim 1, wherein the redox mediator is bound to poly(1-vinylimidazole).

10. 10. The device of claim 1, wherein the excipient comprises phenol.

11. 10. The device of claim 1, wherein the excipient comprises cresol.

12. 2. The device of claim 1, wherein the predetermined distance is 15 millimeters (mm), 14 mm, 13 mm, 12 mm, 10 mm, 9 mm, 8 mm, 7 mm, 6 mm, 5 mm, 4 mm, 3 mm, 2 mm, or 1 mm.

13. 10. The device of claim 1, wherein the amperometric glucose sensor further comprises a reference electrode.

14. 14. The device of claim 13, wherein the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode.

15. 10. The device of claim 1, wherein the amperometric glucose sensor further comprises an insulating layer and a metal layer, the insulating layer bonded to the metal layer, and the metal layer bonded to the electrode layer.

16. 16. The device of claim 15, wherein the insulating layer comprises a polyimide or a liquid crystal polymer.

17. 16. The device of claim 15, wherein the metal layer has a thickness of at least 1 micrometer (μm), 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm.

18. 18. The device of claim 17, wherein the metal layer comprises titanium, gold, or platinum.

19. 10. The device of claim 1, wherein the electrode layer comprises a thin film having a thickness not exceeding 1000 nanometers (nm), 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm, or 100 nm.

20. 10. The device of claim 1, wherein the redox mediator and the enzyme enable electron transfer from subcutaneous glucose to the at least one indicator electrode sufficient to cause the amperometric glucose sensor to respond to subcutaneous glucose concentrations at applied bias potentials not exceeding +200 mV, +150 mV, +100 mV, or +50 mV relative to a reference electrode.

21. 21. The device of claim 20, wherein the applied bias potential of no more than +200 mV, +150 mV, +100 mV, or +50 mV relative to the reference electrode prevents the electrode layer from substantially undergoing electrochemical reaction of the excipient during at least one hour of continuous operation of the amperometric glucose sensor, thereby maintaining sensitivity of the amperometric glucose sensor to the subcutaneous glucose concentration in the presence of the insulin or insulin analog formulation.

22. 22. The device of any one of claims 1 to 21, wherein the ligand comprises a heterocyclic nitrogen compound, a pyridine ring combined with an imidazole ring, a non-nitrogen element substituted in a heterocyclic ring, or a pendant "R" group attached to a heterocyclic ring.

23. 23. The device of claim 22, wherein the heterocyclic nitrogen compound comprises a pyridine or imidazole having one, two, three or four rings.

24. 24. A device according to any one of claims 1 to 23 for use in a method for delivering insulin or an insulin analogue formulation and measuring subcutaneous glucose concentrations, said method comprising the steps of: (a) obtaining a device for delivery of insulin or insulin analog formulations and measurement of subcutaneous glucose concentrations; (b) connecting the proximal end of the hollow tube to a source of the insulin or insulin analog formulation; (c) performing subcutaneous insertion of the distal end of the hollow tube into the subject; and (d) simultaneously (1) subcutaneously delivering said insulin or insulin analog formulation to said subject, and (2) measuring said subject's subcutaneous glucose concentration; The device is a method comprising:

25. 25. The device of claim 24, wherein the subject has type 1 diabetes.

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