Measuring glucose near the insulin delivery duct 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 a current-type glucose sensor located proximal to the distal end of the hollow tube. The current-type glucose sensor may include a redox mediator and an enzyme comprising glucose oxidase or glucose dehydrogenase. Applying a bias potential allows the electrode layer of the current-type glucose sensor to remain substantially free from electropolymerization of the excipients of the insulin or insulin analog formulation during continuous operation of the current-type glucose sensor. The sensitivity of the current-type glucose sensor to subcutaneous glucose concentrations can be maintained in the presence of insulin or insulin analog formulations.

Description

[0001] Cross-references

[0002] This application claims the benefit of U.S. Provisional Application No. 63 / 069,088, filed August 23, 2020, which is incorporated herein by reference in its entirety. Background Technology

[0003] Individuals with diabetes may be at risk of developing complications such as kidney disease, eye disease, cardiovascular disease, and foot / nerve disease. Those who require insulin therapy may have more difficult-to-control blood sugar levels compared to those who do not require it. Individuals with type 1 diabetes (T1D) may require insulin, and many of these individuals use continuous pumps to deliver insulin, which allows for precise, controlled delivery of insulin 24 hours a day. Summary of the Invention

[0004] One valuable technology for managing type 1 diabetes (T1D) is continuous glucose monitoring (CGM), where a subcutaneously inserted sensor provides the user with interstitial glucose data every few minutes. For example, a JDRF-sponsored trial showed that subjects of all ages who used CGM regularly experienced better glycemic control (e.g., as measured by hemoglobin A1C (A1C)) than non-users. However, many subjects may find CGM use cumbersome, and many may only use it occasionally. Unsurprisingly, when CGM is used infrequently or infrequently, its use may not lead to better glycemic control.

[0005] Daily life can be challenging for people who regularly use insulin pumps and CGMs. Such individuals may require two devices inserted through the skin, which can increase the risk of pain, infection, and other side effects compared to a single device. People with T1D may carry multiple devices, such as pumps and / or syringes, CGM receivers, insulin vials, glucose monitors for CGM calibration, as well as glucose monitoring strips and lancets. This device diversity can lead to a condition known as “device burden,” which can cause frustration, anger, and may cause patients to choose between devices rather than using all of them that could improve their health.

[0006] Recognizing the challenges in clinical care and management due to device burden issues, this disclosure addresses the unmet need to integrate CGM and insulin pump cannulas into a single device.

[0007] Manufacturer instructions may specify that the subcutaneous glucose sensor must be positioned away from the insulin pump cannula site. To support this claim, in pig studies, we found that current insulin formulations significantly interfere with currently available hydrogen peroxide measurement sensors. More specifically, we found that preservatives in the formulation, such as phenol and m-cresol, are electroactive and interfere with CGM.

[0008] This disclosure provides an apparatus and a method of using thereof, wherein a glucose sensor can be successfully integrated with an insulin cannula. Such a glucose sensor and insulin cannula can be described, for example, by U.S. Patent No. 10,780,222, which discloses osmium as a redox mediator element and pyridyl and imidazole-based coordination ligands bound to osmium. The apparatus and method of this disclosure may use alternative metals (each of which can be used as a redox mediator) and alternative coordination ligands.

[0009] In one aspect, this disclosure provides an apparatus for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentrations, the apparatus comprising: a hollow tube including a proximal end and a distal end, wherein the proximal end is in fluid communication with a source of insulin or insulin analog formulations, wherein the distal end is configured for subcutaneous delivery of insulin or insulin analog formulations, wherein the insulin or insulin analog formulations contain excipients, including phenol or cresol; and an amperometric glucose sensor located at a predetermined distance from the distal end, wherein the amperometric glucose sensor comprises: an electrode layer including at least one indicating electrode, wherein the electrode layer is located below a redox catalytic layer, the redox catalytic 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.

[0010] In some embodiments, the current-type glucose sensor is located no more than 15 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 14 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 13 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 12 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 11 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 10 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 9 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 8 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 7 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 6 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 5 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 4 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 3 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 2 mm from the distal end. In some implementations, the current-type glucose sensor is located no more than 1 millimeter (mm) from the distal end.

[0011] In some embodiments, the device further includes a housing comprising an upper accessible surface and a lower surface configured for adhesion to a skin surface. In some embodiments, the current-type glucose sensor is disposed on a second hollow tube including a second distal end, wherein the second distal end is configured for subcutaneous insertion. In some embodiments, at least one indicating 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 current-type sensor further includes a reference electrode. In some embodiments, the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. In some embodiments, the current-type sensor further includes 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 an electrode layer. In some embodiments, the insulating layer comprises 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 film with 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 film with a thickness less than about 500 nm. In some embodiments, the metal compound comprises a metal selected from osmium, ruthenium, iridium, iron, cobalt, and any combination thereof.

[0012] In some embodiments, redox mediators and enzymes allow electrons to transfer from subcutaneous glucose to at least one indicator electrode. This electron transfer is sufficient to elicit a response of the current-type glucose sensor to subcutaneous glucose concentration at an applied bias potential relative to a reference electrode of no more than about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV. In some embodiments, the applied bias potential relative to the reference electrode of no more than about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV allows the electrode layer to remain substantially free from excipient electropolymerization during at least one hour of continuous operation of the current-type glucose sensor, thereby maintaining the sensitivity of the current-type glucose sensor to subcutaneous glucose concentration in the presence of insulin or insulin analog formulations.

[0013] In some embodiments, the metal compound includes a metal selected from osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper.

[0014] In some embodiments, the ligand includes a heterocyclic nitrogen compound, a pyridine ring bound to an imidazole ring, a non-nitrogen element substituted with a heterocyclic ring, or an accessory "R" group bound to a heterocyclic ring. In some embodiments, the heterocyclic nitrogen compound includes pyridine or imidazole having one, two, three, or four rings.

[0015] On the other hand, this disclosure provides a method for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentration, the method comprising: (a) obtaining a device for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentration, wherein the device comprises: (i) a hollow tube including a proximal end and a distal end, wherein the proximal end is in fluid communication with a source of insulin or insulin analog formulation, wherein the distal end is configured for subcutaneous delivery of insulin or insulin analog formulations, wherein the insulin or insulin analog formulation comprises an excipient, the excipient comprising phenol or cresol; and (ii) an electrophoretic glucose meter located at a predetermined distance from the distal end. A glucose sensor, wherein the current-type glucose sensor comprises: an electrode layer including at least one indicating electrode, wherein the electrode layer is located beneath a redox catalytic 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 a hollow tube to a source of insulin or an insulin analog; (c) subcutaneously inserting the distal end of the hollow tube into a subject; and (d) simultaneously (1) subcutaneously delivering insulin or an insulin analog to the subject, and (2) measuring the subcutaneous glucose concentration of the subject.

[0016] In some embodiments, the current-type glucose sensor is located no more than 15 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 14 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 13 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 12 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 11 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 10 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 9 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 8 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 7 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 6 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 5 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 4 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 3 mm from the distal end. In some embodiments, the current-type glucose sensor is located no more than 2 mm from the distal end. In some implementations, the current-type glucose sensor is located no more than 1 millimeter (mm) from the distal end.

[0017] In some embodiments, the device further includes a housing comprising an upper accessible surface and a lower surface, and the method further includes adhering the lower surface to the skin surface of an object. In some embodiments, a current-type glucose sensor is disposed on a second hollow tube including a second distal end, wherein the second distal end is configured for subcutaneous insertion. In some embodiments, at least one indicating 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 current-type sensor further includes a reference electrode. In some embodiments, the reference electrode comprises a silver / silver chloride (Ag / AgCl) reference electrode. In some embodiments, the current-type sensor further includes 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 an electrode layer. In some embodiments, the insulating layer comprises 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 film with 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 film with a thickness less than about 500 nm. In some embodiments, the metal compound comprises a metal selected from osmium, ruthenium, iridium, iron, cobalt, and any combination thereof.

[0018] In some embodiments, the method further includes applying a bias potential relative to a reference electrode of no more than about +250 mV, +200 mV, +150 mV, +100 mV, or +50 mV, wherein redox mediators and enzymes allow electrons to transfer from subcutaneous glucose to at least one indicator electrode, such electron transfer being sufficient to elicit a response of the current-type glucose sensor to subcutaneous glucose concentration at the applied bias potential. In some embodiments, applying the bias potential allows the electrode layer to remain substantially free from excipient electropolymerization during at least one hour of continuous operation of the current-type glucose sensor, thereby maintaining the sensitivity of the current-type glucose sensor to subcutaneous glucose concentration in the presence of insulin or insulin analog formulations.

[0019] In some embodiments, the metal compound includes a metal selected from osmium, ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper.

[0020] In some embodiments, the ligand includes a heterocyclic nitrogen compound, a pyridine ring bound to an imidazole ring, a non-nitrogen element substituted with a heterocyclic ring, or an accessory "R" group bound to a heterocyclic ring. In some embodiments, the heterocyclic nitrogen compound includes pyridine or imidazole having one, two, three, or four rings.

[0021] In some implementations, the subject has type 1 diabetes.

[0022] Other aspects and advantages of this disclosure will be readily apparent to those skilled in the art from the following detailed description, in which only illustrative embodiments of this disclosure are shown and described. As will be appreciated, this disclosure is capable of other and different embodiments, and several details thereof can be modified in various obvious ways, all without departing from this disclosure. Therefore, the drawings and descriptions should be considered illustrative in nature and not restrictive.

[0023] Incorporation

[0024] All publications, patents, and patent applications mentioned in this specification are incorporated herein by reference to the extent that each individual publication, patent, or patent application is expressly and individually indicated to be incorporated by reference. If any publication or patent or patent application incorporated by reference contradicts the disclosure contained in this specification, this specification is intended to supersede and / or give precedence to any such contradictory material. Attached Figure Description

[0025] The novel features of the invention are particularly set forth in the appended claims. A better understanding of the features and advantages of the invention will be obtained by referring to the following detailed description and accompanying drawings (also referred to herein as “figures” and “diagrams”) of exemplary embodiments utilizing the principles of the invention, wherein:

[0026] Figure 1 The graph shows the current obtained from a platinum electrode polarized at 600 mV. The initial response to hydrogen peroxide was normal and stable. Subsequent responses to increasing amounts of insulin preparations containing phenolic preservatives initially showed an anodic (oxidative) reaction, followed by a sustained decrease in current, typical of electrode poisoning caused by electropolymerization.

[0027] Figure 2This is a bar chart showing the electrochemical effects of phenol and m-cresol on bare electrodes polarized at many different bias potentials. In particular, very high oxidation currents were observed at those typically high positive potentials used for peroxide detection. For phenol and cresol, the oxidation current decreased significantly with decreasing bias potential. The data obtained with platinum and gold electrodes showed very similar performance. The data shown here are for the gold electrode.

[0028] Figure 3 The structure shown is a polymer repeating unit (poly(1-vinylimidazole)) 1 combined with a member of the redox mediator metal group (defined below) 4 having two 4,4'-dimethyl-2,2'-bipyridine moieties 2 and 3.

[0029] Figure 4 The graph compares the incremental changes in current density of two types of glucose oxidase-based sensors after 20 minutes of exposure to a high dose of mixed phenols (total concentration 180 μg / mL, composed of equal weights of phenol and m-cresol) in the presence of 5 mM glucose. During this period, the current density of each of the three platinum sensors 5 decreased significantly. These sensors were biased at 600 mV. In contrast, the changes in current density of each of the three gold sensors 6 were minimal. These three gold sensors 6 are coated with glucose oxidase and redox mediators bound to ligands and polymers, and biased at 180 mV.

[0030] Figure 5 The graph shows a series of current responses of a gold sensor coated with glucose oxidase and a redox mediator bound to ligands and polymers to a continuously increasing glucose concentration in a phosphate-buffered saline solution sprayed with argon. The response to glucose is substantially linear within this concentration range.

[0031] Figure 6 The graph shows the current signal 7 (small closed symbol) and glucose level 8 (large open symbol) obtained from a glucose oxidase-based platinum hydrogen sensor biased at 600 mV in pigs. When lispro insulin was administered at 105 minutes (indicated by the arrow), the preservative in the formulation immediately caused a very high oxidation reaction, followed by electrode poisoning caused by electropolymerization. At the end of the experiment, despite high glucose levels, the current signal was very small, and the poisoning was evident.

[0032] Figure 7The graph shows the current signal 9 and glucose level 10 obtained from a gold-based sensor in pigs. This sensor is coated with glucose oxidase and a redox mediator bound to ligands and polymers, cross-linked with glutaraldehyde, and biased at 180 mV. Lispro insulin was administered at 105 minutes (indicated by the arrow), and despite the high level of preservatives in this formulation, the current signal 9 did not change. Notably, in the last hour of the experiment, the current 9 rose rapidly in response to significantly elevated blood glucose, thus confirming the absence of electrode poisoning.

[0033] Figure 8 This is a diagram of an in-line filter for removing phenolic substances from an insulin infusion line. A proximal insulin feed line 11 delivers insulin formulation from an insulin pump and connects to the proximal end of a filter 12. A protective membrane 13 prevents filter material from entering the insulin outlet line 14 located distal to the filter. An enlarged view on the right also shows a cylindrical retainer 15 that securely holds the protective membrane 13 and the outlet line 14 to the distal end of the filter 12 without obstructing the passage of insulin.

[0034] Figure 9 This is a graph illustrating the effectiveness of the filter for removing phenolic substances. Aspart insulin was placed near the proximal end of the filter. Multiple samples (0.25 mL each) were then collected during phosphate-buffered saline (PBS) delivery. Insulin assay results 16 (estimated by measuring total protein using a dicaprinate [BCA] assay) are quantified on the left axis, while phenol assay results 17 (using a nitroprusside-based assay) are quantified on the right axis. The filter material was Sephadex G10 (medium). Insulin passed through the filter quickly after delivery, while phenolic substances emerged much later, only after 3 mL had passed through the filter.

[0035] Figure 10 The steps for creating patterns of electrodes and interconnect traces using micromachining are illustrated. After laminating a titanium foil onto polyimide, a layer of silver is sputtered onto the titanium, followed by a layer of photoresist. Some of the photoresist 18 is selectively removed to make unwanted silver available for removal by an etchant. After removing the remaining photoresist, the silver electrode pattern 19 is exposed. After applying the next layer of photoresist, platinum 20 is then deposited by sputtering. When the photoresist is removed, unwanted platinum is stripped away, exposing a platinum electrode pattern 21. The next layer of photoresist 22 is applied and selectively removed. If no photoresist is available, unwanted titanium can be etched away. When the photoresist 23 is removed, the correct titanium pattern 23 is exposed. Detailed Implementation

[0036] While various embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided by way of example only. Many variations, modifications, and substitutions will occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.

[0037] Whenever the terms "at least," "greater than," or "greater than or equal to" precede the first value in a series of two or more values, the terms "at least," "greater than," or "greater than or equal to" apply to each value in the series. For example, greater than or equal to 1, 2, or 3 is equivalent to greater than or equal to 1, greater than or equal to 2, or greater than or equal to 3.

[0038] Whenever the terms "not exceeding," "less than," or "less than or equal to" precede the first value in a series of two or more values, the terms "not exceeding," "less than," or "less than or equal to" apply to each value in the series. For example, less than or equal to 3, 2, or 1 is equivalent to less than or equal to 3, less than or equal to 2, or less than or equal to 1.

[0039] As used herein, the term "object" generally refers to a person, individual, or patient. An object can be a vertebrate, such as a mammal. Non-limiting examples of mammals include humans, apes, farm animals, racing animals, rodents, and pets. An object may be a person with diabetes or suspected of having diabetes. An object may exhibit symptoms indicative of its health or physiological state or condition, such as diabetes. Alternatively, an object may be asymptomatic in relation to such health or physiological state or condition.

[0040] A valuable technique for managing type 1 diabetes (T1D) is continuous glucose monitoring (CGM), where a subcutaneously inserted sensor provides the user with interstitial glucose data every few minutes. For example, a JDRF-sponsored trial may show that subjects of all ages who regularly use CGM experience better glycemic control (e.g., as measured by hemoglobin A1C (A1C)) than non-users. However, many subjects may find CGM use cumbersome, and many may only use it occasionally. Unsurprisingly, when CGM is used infrequently or infrequently, its use may not lead to better glycemic control.

[0041] Daily life can be challenging for people who regularly use insulin pumps and CGMs. Such individuals may require two devices inserted through the skin, which can increase the risk of pain, infection, and other side effects compared to a single device. People with type 1 diabetes (T1D) may carry multiple devices, such as pumps and / or syringes, CGM receivers, insulin vials, glucose monitors for CGM calibration, as well as glucose monitoring strips and lancets. This device diversity can lead to a condition known as “device burden,” which can cause frustration, anger, and may cause patients to choose between devices rather than using all of them that could improve their health.

[0042] Recognizing the challenges in clinical care and management due to device burden issues, this disclosure addresses the unmet need to integrate CGM and insulin pump cannulas into a single device.

[0043] The manufacturer's instructions may indicate that the subcutaneous glucose sensor must be positioned away from the insulin pump cannula site. To support this claim, in a study in pigs, we found that current insulin formulations significantly interfere with currently available hydrogen peroxide measurement sensors. More specifically, we found that preservatives in the formulation, such as phenol and m-cresol, are electroactive and interfere with CGM.

[0044] This disclosure provides an apparatus and a method of using thereof, wherein a glucose sensor can be successfully integrated with an insulin cannula. Such a glucose sensor and insulin cannula can be described, for example, by U.S. Patent No. 10,780,222, which discloses osmium as a redox mediator element and pyridyl and imidazole-based coordination ligands bound to osmium. The apparatus and method of this disclosure may use alternative metals (each of which can be used as a redox mediator) and alternative coordination ligands.

[0045] It may be necessary to create a single combined device, rather than using separate insulin infusion catheters and CGM sensors. For such combined sensing catheters, many different glucose sensing strategies can be considered. For example, optical sensing techniques can be used for glucose. Optical glucose sensors can be built 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 assay reagents. Porous hollow sensors can contain porous beads for optical determination of analyte concentration. Alternative sensing strategies, such as viscosity measurements, can be used. However, all of these can present challenges when attempting to pair CGM with drug infusion (e.g., in a single device or in a subcutaneous setting).

[0046] Common analyte sensor designs are based on the principle of current measurement, where analytes are detected by generating an electrochemical signal associated with the analyte of interest. Sensing electrodes can be fabricated using a sputtered or evaporated thin film deposited on a substrate surface. 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 coupled to a reference electrode (such as silver / silver chloride), redox-active analytes can be detected by current measurement. By adding an enzyme layer such as glucose oxidase, the sensor can be made specific for the analyte glucose. Glucose oxidase may be able to convert glucose (which may not be easily detected by current measurement) into hydrogen peroxide (which may be easily detected (e.g., using a sensor)). When a thin film of a metal electrode is deposited on a suitable polymer film (such as polyimide), the resulting sensor can have the additional advantage of flexibility. For example, users may find rigid catheters or needles uncomfortable or painful.

[0047] The problem with electrodes made of thin metal films can be their fragility; these layers may delaminate when exposed to physical trauma such as impact, buckling, shear stress, and tensile stress. For example, the durability of thin-film electrodes may be limited.

[0048] More specifically, a large number of buckling cycles can lead to material failure, a phenomenon known as cyclic fatigue. While the durability of a thin film may be sufficient for short-term applications, long-term dynamic sensing applications may require greater resilience to trauma. In the case of indwelling subcutaneous sensors, the sensor may need to withstand repeated impacts and / or repeated buckling for 3 to 7 days or longer. Thin metal films may crack, which can be exacerbated by immersion in moist, high-salt environments, such as those presented by mammalian blood or subcutaneous interstitial fluid. Therefore, electrodes in commercial CGM sensors (e.g., manufactured by Dexcom, Inc.) can be made of durable solid wires instead of thin films. Examples may include wire-based variable stiffness percutaneous medical devices, wire-based percutaneous implantable continuous analyte sensors with siloxane membranes, biointerfaces for wire-based sensing electrodes, percutaneous analyte sensor assemblies, flexible solid wire-based glucose sensors, multi-electrode wire-based sensors, and multilayer sensors with solid cores. However, wires or rods with solid cores may therefore be incompatible with drug delivery, such as insulin, which may require hollow lumens. Due to the lack of a hollow lumen, these devices may face challenges in applications such as combined analyte sensing and drug delivery.

[0049] Other devices may use sensors coupled to a hollow catheter (e.g., a glucose sensor disposed within the hollow catheter). More specifically, the sensor may be disposed within a larger-diameter catheter placed within a blood vessel. While such a device may be suitable for measuring fluid (blood) present within the catheter, such a design may not be suitable for sensing catheters used to measure glucose in subcutaneous adipose tissue. For use in subcutaneous tissue, the sensing element may need to be located on the outer wall of the hollow catheter. Typically, an "in-tube lead sensor" or "in-tube" design may not allow for proper functioning in subcutaneous tissue. For drug delivery, the lumen may need to be hollow. For example, consider a device having a sensing element located within a hollow portion and designed to measure analytes within the lumen. For an effective subcutaneous sensing catheter, an open interior (lumen) may be required to allow drug delivery into the body. In embodiments of the devices disclosed herein, an outer wall that is not in contact with the drug and is soaked in a glucose-containing subcutaneous interstitial fluid is a suitable location for the sensing element.

[0050] Other sensor configurations may require removing fluid samples from the body for sensing. For example, a hollow fiber-based glucose sensor might involve dialysis with a test solution. As another example, a hollow probe could be used to extract interstitial fluid. As yet another example, a hollow electrochemical unit with an internal sensing element might be needed to extract fluid samples. As yet another example, a glucose dehydrogenase-based sensor could include an interstitial fluid sampling device. As yet another example, a method for determining glucose concentration might require a device with an external sensor coupled to a fluid sampling pump. As yet another example, the sensor could incorporate a hollow component and a lancet for sampling interstitial fluid. As yet another example, the system could incorporate a microdialysis-based sensor. As yet another example, the sampling device could incorporate a vacuum for extracting blood samples from the skin surface. These devices may face challenges in applications that allow for continuous drug delivery while the sensor is exposed to interstitial fluid. Therefore, these systems may be incompatible with continuous subcutaneous drug infusion.

[0051] Other sensor configurations can utilize microneedles to reduce the invasiveness of measurement techniques. However, microneedle arrays may face the challenge of keeping all microneedles lodged in mammalian tissue during body movement. Due to the short length of the microneedles, many may tend to dislodge from the tissue when a person moves suddenly or forcefully. This problem of unintentional implantation may make it unsuitable for long-term use in outpatient settings.

[0052] For example, a uniform hollow structure could be used for analyte sensing and drug delivery. While insulin could be used, such a device might not be immune to oxidative interference from preservatives, nor could it avoid the fragility of the thin metal electrodes laminated onto the hollow structure. Similarly, the device might not be able to measure glucose in the presence of insulin preservatives and / or might not be able to avoid the problem of the thin metal electrodes being fragile.

[0053] To fabricate combined sensors / conduits, biosensing elements can be incorporated into the walls of hollow needles or conduits. For example, fabrication may include directly depositing a thin-film metal (e.g., platinum, gold) indicating electrode and a thin-film silver (Ag / AgCl) reference electrode onto a lower polymer layer such as polyimide or polyester. One such design could incorporate a printed electrode membrane. However, in vivo animal studies have revealed significant problems with sensing conduits made from thin-film metal electrodes deposited on polymer layers. In particular, these sensors exhibit frequent delamination and a general lack of durability.

[0054] At many bias potentials, insulin preservatives (phenol and m-cresol) near the glucose sensing indicator electrode can generate large currents (electron flows), which can be difficult to distinguish from high glucose levels. More specifically, when the indicator electrode in the presence of preservatives is polarized at a high bias potential, large currents can occur even in the absence of glucose. Therefore, a way to reduce or eliminate glucose-like currents is to use a much lower bias potential. If a hydrogen peroxide sensing system is used, it may be difficult to obtain sufficient glucose current from peroxide oxidation while minimizing interference from insulin preservatives.

[0055] Conversely, if certain systems operating at low bias potentials are used, such as redox mediators (e.g., metal-based, such as osmium, ruthenium, iridium, iron, and cobalt), electrons can be transferred from glucose to the indicating electrode without interference from the insulin preservative. Examples of metal selections that can be used as mediators are disclosed herein. Mediators can bind to coordinating ligands, and several options for coordinating ligands are disclosed herein. Mediator-ligand complexes can be attached to polymers, such as polyvinylpyridine or polyvinylimidazole, which can be further cross-linked and immobilized on the sensor surface by a bifunctional cross-linking agent.

[0056] As an alternative to or in combination with redox mediator chemistry, specialized filters can be used to capture phenol and m-cresol before delivery to the object, thereby preventing these compounds from reaching the subcutaneous space and generating interfering currents. Because these filters prevent phenol and m-cresol from reaching the subcutaneous space and from reaching current-based sensors, such filters can be used in conjunction with sensors employing conventional hydrogen peroxide detection (e.g., platinum-based sensors that do not contain redox mediators).

[0057] Regardless of whether redox mediators or filters are used, a device may malfunction if the layers of the sensing conduit are not durable. For example, if the thin metal film constituting the indicating electrode is deposited directly on a polymer substrate, the electrode film may be weak and not durable. Instead, it may decompose and / or delaminate from the polymer during use.

[0058] To avoid this fragility while minimizing costs, it may be necessary to laminate a thin metal electrode film onto an underlying metal layer (such as titanium). For sufficient strength, this metal may need to be much thicker than the electrode film.

[0059] To reduce device burden, it may be necessary to be able to continuously measure glucose at the direct site of insulin delivery, especially in the subcutaneous interstitial fluid. To better understand the response of electrodes or sensors in the presence of insulin formulations, [further details needed]. Figure 1 The experiment is shown. This figure illustrates the response of a platinum electrode (polarized at 600 mV, compared to an Ag / AgCl reference electrode) studied in phosphate-buffered saline (PBS). (For definitional purposes, the term reference electrode in this disclosure refers to a reference electrode in a three-electrode system or a combination of a reference-counter electrode or a reference-auxiliary electrode in a two-electrode system). The electrode was bare, i.e., not coated with an enzyme or outer membrane. Initially, hydrogen peroxide (H₂O₂) was added, and the electrode responded rapidly and maintained a stable current. At 13 minutes, a standard commercially available insulin formulation (insulin aspart, Novo Nordisk) was added, making the total concentration of phenol and m-cresol (phenolic substances) equal to 45 μg / mL. It can be clearly seen that a rapid oxidation (rise) current appears immediately after administration of the insulin formulation. However, the rise in current is brief, and after a few minutes, the current begins to decline despite the continued presence of phenolic substances. At 23 minutes and 33 minutes, more insulin aspart was administered, resulting in a much higher concentration of phenolic substances, as shown in the figure. Importantly, it is noteworthy that after these subsequent additions, the current did not increase; instead, it continued to decrease, resulting in a final current significantly lower than the original current obtained from H₂O₂ (which is also retained in solution). This gradual current loss is due to electrode poisoning. More specifically, phenol and cresol undergo an electropolymerization process in which a thin insulating polymer layer forms on the electrode surface. This layer is essentially impermeable to many analytes, including H₂O₂, and therefore, such an electrode is useless for measuring glucose or other analytes after exposure to phenolic substances.

[0060] Another experiment (not shown) was conducted using preservative-free insulin (brand name Gibco, purchased from Thermo Fisher Life Technologies). This insulin did not induce any electrochemical reactions or electrode poisoning. This experiment demonstrates that... Figure 1The interference mentioned in the text is due to preservatives, not insulin itself.

[0061] Then, we decided to investigate the effect of the bias potential on the electrochemical responses of phenol and cresol, such as Figure 2 As shown. 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 cleaned between tests to remove any electropolymers. The results showed that the response to phenols was highly dependent on the magnitude of the bias potential. In particular, a very large oxidation reaction occurred when the potential was increased to high potentials, such as those exceeding 350 mV. Conversely, the response was quite low when the bias was decreased, especially below 250 mV.

[0062] To minimize interference by lowering the bias potential, we conducted experiments using a redox-mediated chemical scheme. Another metal (such as ruthenium, iridium, iron, or cobalt) can be substituted for osmium to produce similar results.

[0063] Redox mediator complexes (e.g., based on metals such as osmium, ruthenium, iridium, iron, and cobalt) may be suitable compounds for accepting electrons from glucose oxidases, more specifically, from the cofactor of a glucose oxidase called flavin adenine dinucleotide (FAD). The metal used as a 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 be used as a redox mediator; however, one advantage of the redox mediator metal group is that its members are much less expensive than osmium. In embodiments, members of the redox mediator metal group are coordinated with ligands such as 4,4'-dimethyl-2,2'-bipyridine and also bound to a PVI polymer. Many other ligands can be used, some of which are disclosed herein. Binding to PVI prevents the redox mediator ligand from dissociating from the polymer backbone.

[0064] It should be understood that 4,4'-dimethyl-2,2'-bipyridine is just one example of a suitable coordination ligand. Members of the coordination ligand class include, but are not limited to, the following:

[0065] (1) Heterocyclic nitrogen compounds having one, two, three, or four rings, such as pyridine or imidazole;

[0066] (2) A ligand in which one or more pyridine rings are bound to one or more imidazole rings;

[0067] (3) One or more non-nitrogen elements are substituted into the ligands in the heterocycle; and

[0068] (4) Ligands in which other chemical groups are bonded to heterocyclic atoms. These groups are usually referred to as “R” groups or accessory groups.

[0069] When bound to redox mediator metal members, electron-donating groups (such as methyl, methoxy, or amino groups) allow the redox mediator metal members to transfer electrons at a lower polarization bias. Redox mediator metal members, along with coordinating ligand members, can be referred to as redox mediators. To improve functionality, redox mediators can be bound to polymers, and these complexes can be called redox mediator polymers (RMPs). RMPs can be crosslinked with reagents such as glutaraldehyde or polyethylene glycol diglycidyl ether (both linked to amino groups).

[0070] In some implementations, RMP is deposited on a gold indicator electrode, but other materials such as vitreous carbon, glassy carbon, graphite, platinum, or iridium can also be used. The indicator electrode can also be made porous, for example, by using acid anodizing, laser pore formation, or plasma etching.

[0071] In some embodiments, the RMP is coated with a polymer layer known as an outer membrane. Oxygen permeability is unnecessary for the function of this type of sensor, but a certain degree of glucose permeability is required. The outer membrane can be made of polyurethane, Nafion, poly(vinylpyridine), poly(vinylpyridine)-styrene copolymer, molecular weight cutoff polymer membranes, siloxanes, hydrogels, and many other materials that allow glucose permeation.

[0072] For the exemplary experiment shown here, we used Figure 3 The compound shown is a member of the redox mediator metal group. The polymer backbone 1 consists of poly(1-vinylimidazole) (PVI). Two coordinating ligands, 4,4'-dimethyl-2,2'-bipyridine 2 and 3, bind to member 4 of the redox mediator metal group. Member 4 of the redox mediator metal group binds to approximately one of every 5 to 15 imidazole groups on the PVI.

[0073] Using an RMP-based sensor and a conventional platinum H2O2 sensing sensor, we subsequently conducted... Figure 4 The in vitro experiments are shown. In this experiment, a gold sensor coated with RMP, glucose oxidase, and an outer membrane was compared with a platinum sensor coated with glucose oxidase and an outer membrane. The RMP-based sensor was biased at 180 mV, while the platinum sensor was biased at 600 mV. After initial exposure to 5 mM glucose solution, platinum-based sensor 5 and RMP-based sensor 6 were then exposed to incremental amounts of commercially available insulin aspart formulations containing phenolic compounds (Novo Nordisk), such as... Figure 1 As described in the early experiments shown. Figure 4 The incremental responses are shown only at the highest phenolic concentration (180 μg / ml). Each bar represents the result for a single sensor. It should be noted that a large negative response is observed in the conventional platinum-based sensor 5, while only a small positive response is observed in the RMP-based gold sensor. As previously discussed, this large negative response reduces the sensor's response to a level far below the original response to glucose (which remains in solution), thus demonstrating the extent of electrode poisoning. As a follow-up to this experiment (not shown), both the platinum-based and RMP-based gold sensors were removed from solution, rinsed, and re-exposed to 5 mM glucose. The platinum-based sensor showed a very low, almost negligible, response to glucose (confirming permanent poisoning), but the RMP-based sensor responded rapidly, almost identical to the original response to glucose. Another metal (such as ruthenium, iridium, iron, or cobalt) can be used to replace osmium to produce similar results.

[0074] Figure 5 The response of an RMP-based sensor with a gold indicator electrode and an Ag / AgCl reference electrode to a stepwise increase in glucose concentration in phosphate buffer during continuous argon injection is shown. In this case, the RMP and glucose oxidase are cross-linked with polyethylene glycol glycidyl ether, but similar results were obtained using liquid glutaraldehyde or glutaraldehyde vapor. Note that the response to glucose up to at least 25 mM is substantially linear.

[0075] The aforementioned series of experiments demonstrates that a gold sensor coated with RMP and cross-linked glucose oxidase and polarized at 180 mV, compared to Ag / AgCl, can measure glucose with little or no interference from preservatives used in insulin formulations. In contrast, a platinum sensor coated with cross-linked glucose oxidase and polarized at 600 mV experiences a very large initial oxidation current when exposed to phenolic substances. Furthermore, if such exposure continues for more than a few minutes, the electrode remains poisoned by a dense layer of electropolymerized phenolic compounds, preventing H2O2 and other common analytes from reaching the indicating electrode and being measured. Other metals (such as ruthenium, iridium, iron, or cobalt) can replace osmium to produce similar results.

[0076] Subcutaneous devices are exposed to a variety of types of trauma, such as from physical movements and impacts common in daily life. Therefore, even if the chemical layer on the electrodes can successfully measure glucose without interference from phenol and cresol, a dual-purpose sensing catheter may not function accurately throughout its entire lifespan unless the catheter has a durable, robust construction.

[0077] One method for creating a continuous sensor embedded in 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 materials and processes are not chosen correctly, the resulting electrode layer can be very fragile. More specifically, the device becomes fragile if a thin-film metal electrode material (thickness less than 100 nm) is placed directly on a polymer surface (with or without an underlying thin adhesive layer, such as Ti, Au, or Ni). The electrode film often delaminates or disintegrates during impact, making such a device unsuitable for use as a catheter left in the subcutaneous space for several days. In fact, noticeable electrode delamination can be seen after only a few hours of in vivo use in such a design. Based on the inventors' experience, such a design, regardless of whether a 25-200 nm connecting (adhesive) layer is deposited under the electrode, leads to frequent separation of the connecting layer from the polyimide, frequent separation of the indicating or reference electrode film from the connecting layer, and frequent fragmentation of the metal layer.

[0078] On the other hand, placing a metal foil beneath the thin-film metal electrode significantly improves durability and fatigue resistance while maintaining sufficient flexibility in fabrication and use as a biosensor. The term "foil" is used to refer to a metal layer with a thickness of at least 2 micrometers (μm), much thicker than thin-film layers typically deposited by sputtering, evaporation, printing, or electroplating. Foils may possess beneficial mechanical properties. For these reasons, metal foil (beneath a thin electrode film) is ideally suited for durability purposes.

[0079] All layers of the sensing conduit must be tightly bonded to adjacent layers. One method to create an interface with good adhesion and durability is to use a laminator under high temperature and pressure. A high-viscosity adhesive, such as grade B acrylate, is placed at the interface between the foil and the underlying polymer, bonding the two materials together. After lamination, the thin-film electrode material can be deposited on a durable metal foil. The thickness of the metal foil is typically 2–15 μm.

[0080] The metal used to construct the foil must be carefully selected. In the case of current-type glucose sensors, the indicating electrode is typically platinum, gold, or carbon. Copper (often used as foil in flexible electronic circuits) is unsuitable for biosensors. Specifically, the connection of these dissimilar metals can generate a large current if there is simultaneous physical contact between the interstitial fluid, copper, and platinum. A suitable foil candidate is titanium, which is inexpensive and we found that it generates little or no current when paired with platinum. Silver and copper are unsuitable as foil materials. Gold has moderate value.

[0081] Using the durable sensing catheter design discussed above, we conducted a series of studies in non-diabetic eucatan miniature pigs weighing 33–60 kg. For the preparation of this study, sensing catheters were fabricated. A 12.5 μm thick polyimide strip was laminated with a 5 μm thick titanium foil sheet. Three 1 mm thick...2 A thin-film platinum indicator electrode and an Ag / AgCl reference electrode are sputtered onto a titanium foil surface. The electrode strip is wound and laminated onto the outer surface of a blunt, hollow 21-gauge stainless steel tube using an epoxy resin adhesive designed for high-salt, humid environments. The indicator electrode is coated with glucose oxidase and bovine serum albumin (BSA) in a 3:2 ratio and crosslinked with glutaraldehyde vapor, then coated with a siloxane-polyurethane copolymer outer film (Lubrizol, Inc.). Such a dual-purpose device is termed a “glucose-sensing conduit” or simply a “sensing conduit.” A series of interconnecting traces emanate from the three indicator electrodes and a single reference electrode, terminating in a body-worn electronic sensor module electrically continuous with the sensing conduit. The sensor module contains a battery and a Bluetooth-enabled transceiver that transmits electrochemical signals to a personal computer or mobile phone.

[0082] Under isoflurane anesthesia, multiple sensing catheters attached to telemetry sensor modules were inserted into the subcutaneous tissue of the pig's abdomen. The sensor modules were adhered to the skin with cyanoacrylate adhesive, and each pig was then allowed to recover from anesthesia. The animals were anesthetized again with isoflurane the following morning. After a stabilization period, a normal blood glucose clamp was performed for 5 hours. More specifically, to avoid hypoglycemia, 20% dextran was administered intravenously according to a computer algorithm. At the 105th minute of the clamping period, as... Figure 6 As indicated by the arrows, lispro insulin (a total dose of 0.22 units per kg, distributed between two catheters, such that 0.11 units per kg are delivered through each catheter) is administered via some sensing catheters. Insulin is not delivered via other sensing catheters.

[0083] Figure 6Exemplary average data obtained from several sensing catheters delivering lispro insulin are shown. Electrochemical sensor current 7 and blood glucose value 8 (repeatedly measured using a Bayer Contour Next meter) are indicated by arrows. Note the very large current spike immediately after insulin administration, followed by a rapid exponential decline. Later in the experiment, at 300 minutes, a rapid intravenous infusion of 20% dextran resulted in a significant increase in blood glucose, reaching almost 300 mg / dL. It can be seen that the sensor cannot respond forcefully to the significant increase in glucose levels. During hyperglycemia, the current rise was only small, typical of sensors experiencing electrode poisoning. Many such experiments have been conducted in pigs. In summary, in approximately 40% of the experiments administering lispro insulin, a significant oxidative increase in current occurred between 105 and 165 minutes, despite stable glucose levels. In these cases, the insulin preparation likely flows back onto the sensor element after leaving the catheter, generating an oxidative signal. In other cases, the insulin preparation likely flows out of the catheter without contacting the sensing element, thus failing to induce an interfering signal. Another metal (such as ruthenium, iridium, iron, or cobalt) can replace osmium to produce similar results.

[0084] Other pig experiments were conducted using a sensing conduit with a gold indicator electrode and an RMP that binds to glucose oxidase via glutaraldehyde. Figure 7 Mean data from several RMP-based gold sensors delivering lispro insulin are shown. Consistent with the in vitro data discussed above, there was little evidence of interference from insulin preservatives after administration of the insulin formulation. When lispro insulin was administered at 105 minutes, the sensor current 9 did not increase. Furthermore, in the last hour of the study, the RMP-based sensors responded strongly to significant hyperglycemia. Note the rapid rise in blood glucose during the last hour of the study. The rapid increase in current 9 during this rise confirmed the absence of electrode poisoning. Other metals (such as ruthenium, iridium, iron, or cobalt) could replace osmium to produce similar results.

[0085] We also discovered another method to avoid oxidative currents caused by preservatives: using a filter placed in the insulin infusion line. For example, a hydrophobic zeolite filter can be used to remove insulin preservatives from the insulin vial before injection. In the implementation, we teach the use of an in-line filter designed for diabetic patients using a portable insulin pump for subcutaneous insulin delivery. Such a filter... Figure 8Depicted in the image. A plastic tube from insulin pump 11 is attached to a filter sleeve 12 filled with filter material. At the distal end of the filter sleeve is a protective membrane 13, which prevents filter beads or particles from being released into the insulin tubing (and thus into the patient's body). One such embodiment of this protective membrane is porous cellulose acetate with pores smaller than the filter bead material. Many other membrane compositions and pore sizes are suitable for manufacturing protective membranes. Tube 14 carries the filtered insulin from the filter sleeve into the sensing catheter. Figure 8 The right-hand side of the diagram shows an enlarged view of the filter with additional details. Typically, a retainer device 15 is required to securely hold the filter sleeve 12, protective membrane 13, and outlet pipe 14 in place. In some embodiments, it is also desirable to place the retainer device near the end of the filter.

[0086] Many such beaded or particulate materials are available for filtering phenolic substances from insulin formulations. Some of these materials include those commonly used in size exclusion chromatography (also known as gel filtration chromatography and molecular sieve chromatography). As used herein, size exclusion media can be porous particles that trap smaller molecules while allowing larger molecules to pass through easily. In one embodiment, preservatives (including m-cresol and phenol) contained in the insulin formulation are trapped in the pores. Larger insulin molecules (not trapped) pass through the filter easily.

[0087] A suitable filter material is cross-linked dextran, one brand of which is... Sephadex G10 is suitable because it is used to separate compounds smaller than 700 Daltons from those larger than 700 Daltons. This grade of cross-linked dextran is suitable because cresol and phenol weigh approximately 100 Daltons, while insulin and insulin analogs weigh approximately 5800 Daltons. Other grades of cross-linked dextran can also be used. Besides dextran, other options for filter materials include carbon (including charcoal and activated carbon), alumina, silicates, silica, mixtures of alumina and silica (called zeolites), and other compounds used to separate compounds based on molecular size. Materials commonly used in reversed-phase high-performance liquid chromatography can also be used to separate molecules based on hydrophobicity / hydrophilicity. Phenol and cresol are more hydrophobic than insulin.

[0088] Figure 9 The results of an experiment conducted to isolate insulin aspart from its preservative are shown. The mixture was manufactured using 40–120 μm Sephadex Medium G10 beads (GE Healthcare, Inc.) and… Figure 8A similar filter was used. Ten units of aspart insulin were placed on a column with a diameter of 3 mm and a length of 64 mm. Subsequently, 0.25 mL of PBS was delivered every 5 minutes via an insulin pump, and an equal volume of eluent was collected every 5 minutes. Insulin in the eluent was repeatedly measured using the BCA total protein assay (trace 16 in the figure). Phenol was repeatedly measured using a nitroprusside-based spectrophotometric endpoint assay (trace 17). The results showed that insulin eluted very early in the experiment, with little or no additional insulin emerging after the second collection. Conversely, phenol eluted only late in the experiment, after a collection of 3 mL. These results indicate that this implementation is effective for diabetic patients using insulin pumps. Currently available pumps contain a maximum of 3 mL of insulin formulation in their reservoirs. Therefore, for pump users using such a filter, phenolic substances may not appear during the 3-day usage period, during which no more than 3 mL of insulin formulation can be administered.

[0089] One variation in the use of filter materials involves electrical connection to the filter material, removing interfering substances electrochemically. For example, activated carbon filter particles filled and immersed in a brine solution are conductive; thus, the carbon can be used as an indicator electrode, polarized by a power supply at 400-800 mV to a suitable reference electrode, such as an Ag / AgCl electrode. In such a case, to avoid short circuits, the reference electrode cannot contact the carbon, so a sheath can surround the reference electrode. The sheath prevents contact with the carbon, while the brine allows electron flow to complete the anodic-cathode circuit. When properly biased, the carbon oxidizes and electropolymerizes phenols and m-cresols, preventing them from passing through the filter. In such a filter, some phenols can be normally adsorbed onto the carbon, while others are electropolymerized into a thin plastic layer, remaining on the carbon in a disposable filter. Using electropolymerization and adsorption is more efficient than adsorption alone.

[0090] Importantly, it should be noted that, in addition to Figure 8 Beyond the single long tubular structure shown, filters can take on various physical forms. For example, a filter can loop back to itself multiple times in a serpentine manner. Such a design would not occupy as much longitudinal distance.

[0091] For use in people with diabetes, the filter can be placed anywhere in the insulin delivery line, such as the insulin reservoir (usually placed with the pump), the insulin tubing, or in the insulin fluid path immediately adjacent to the inlet of the fluid-into-sensing catheter within a skin-worn sensor module.

[0092] When using a filter, a higher polarization potential bias can be used so that the sensing system can utilize standard hydrogen peroxide sensing. In this case, a redox mediator is not required. To optimize the signal from hydrogen peroxide, a high bias, such as exceeding 500 mV, is typically used. Alternatively, the filter can be used in combination with a redox-mediated system with a lower bias. The advantage of such a combination is that it uses two effective methods to significantly reduce the adverse effects of phenol and cresol during CGM.

[0093] The above description explains the use of a filter to remove phenolic substances from the insulin delivery line after the insulin preparation has been placed in the pump reservoir but before the insulin is pumped into the dual-purpose sensing catheter. However, it should also be noted that such a filter can be used in standard insulin infusion devices (without a glucose sensor). It is important to note that phenol and m-cresol have numerous toxic effects. These compounds have been linked to cancer, particularly bladder cancer. The U.S. Environmental Protection Agency cites the association between phenolic drug administration and weight loss and neurotoxicity, and classifies m-cresol as a Group C (possible human carcinogen). Furthermore, these compounds are associated with many other side effects, including inflammation at the insulin site. Recently, phenolic compounds have been clearly demonstrated to be cytotoxic to mammalian cells.

[0094] For these reasons, many insulin users may decide they do not want to be exposed to the high concentrations of phenols present in all insulin preparations used by humans. Therefore, even without a sensing catheter, an insulin infusion kit with a phenol filter is a useful device for people using infusion pumps. For those who do not use an insulin pump, the same filter material can be used to remove phenols from commercial insulin preparations before injection.

[0095] Example 1: Sensing conduit based on redox mediator

[0096] Laminating metal foil onto a polymer substrate

[0097] Objective: This step creates a titanium and polyimide (Ti / Pi) laminate. In this embodiment, the Ti thickness is 5 μm and the polyimide thickness is 12.5 μm, but these dimensions should not be considered limiting. This embodiment creates a laminated rectangle with dimensions of 60 mm x 85 mm.

[0098] Materials include deionized water; polyimide sheets with grade B acrylate adhesive; titanium foil; pressure pads; Teflon sheets and graphite plates; and a heated hydraulic press capable of reaching 400 degrees Fahrenheit.

[0099] Sheet setup process: Between the pads (pressure application) of the hydraulic press, the materials should be stacked in the following order, from bottom to top: graphite pressure plate; pressure pad; titanium foil; polyimide with Class B adhesive facing the titanium foil; pressure pad; graphite pressure plate.

[0100] Before handling polyimide and titanium, prepare graphite plates, graphite foil, and Teflon sheets. All sheets should be cut to the size of the pad and cleaned with isopropyl alcohol (IPA), then carefully inspected for lint or contaminants.

[0101] For press operation: Stack the sheets in the hydraulic press and apply a force of 5000 lb to the pads. Set the temperature of the top and bottom plates to 375 degrees Fahrenheit. Once both pads have reached 375 degrees Fahrenheit, set the pressure to 15000 lb and hold for 1 hour. Allow the pads to cool to below 100°F, then remove the stack of sheets from the press.

[0102] General equipment and supplies (for all the following steps): double-sided polyimide tape; plastic cards; razor blades; 50x75mm glass slides; isopropyl alcohol (IPA); deionized (DI) water; Pt (platinum) target; Ag (silver) target; aluminum foil; Ar (argon) plasma etching machine; quartz crystal microbalance (QCM); sputtering tools; hot plate; mask aligner - such as OAI 200 desktop mask aligner; spin coater with a speed of 300 RPM; argon gas source.

[0103] Preparation of TI / PI laminates for gold and silver electrode applications

[0104] Clean the slide with soap and tap water, IPA, DI, and Ar plasma for 1 minute; dry. Place double-sided polyimide tape on a hot plate. Apply the polyimide tape, removing air bubbles. Place aluminum foil on the hot plate; apply double-sided polyimide to the slide, with the rigid backing adhesive side up. Apply Ti foil to the rigid backing. Apply Ti / polyimide and the rigid backing to the polyimide tape. The stacking order should be (from bottom to top): slide, double-sided polyimide tape, rigid backing, Ti / polyimide laminate with Ti side up.

[0105] Silver film deposition

[0106] Objective: To deposit a layer of Ag (later chlorinated to Ag / AgCl) to form a reference electrode. The nominal thickness is 400 nm to allow for a reasonable thickness of Ag / AgCl after chlorination (chlorination reduces the thickness of Ag). Silver sputtering is used in this process, 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 apparatus such as a CRC-100, an Ag target, and compressed Ar gas.

[0107] To sputter the Ag layer, the substrate is placed in the sputtering apparatus, and the vacuum pump degasses any exposed binder. The sputtering chamber is filled with Ar, and the operator allows the system to be equilibrated to 7 mTorr. Sputtering continues until the quartz crystal microbalance (QCM) reading for Ag is 5.00 kA (500 nm). (Gain = 75, Density = 10.5, Z-ratio = 0.529, Tooling factor = 256). The apparatus is removed from the sputtering apparatus. A tape test is performed at the corners using 3M Magic Scotch tape to ensure good adhesion. Store in a clean, covered container.

[0108] AG patterning and etching (removal of unwanted AG).

[0109] For drawings of the main micromachining (electrode patterning) steps, see [link / reference]. Figure 10 Objective—To pattern Ag pads on a Ti / PI substrate using photoresist. Materials: 50x75mm silver-sputtered Ti / PI substrate on a glass slide; NaOH microspheres; 300mL beaker; 250mL beaker; optical mask; S1813 (photoresist); 80 / 20 primers (80% propylene glycol monomethyl ether acetate and 20% hexamethyldisilazane (HMDS) primers). Materials used in the cleanroom included a mask aligner; rotator; hot plate; DI water; balance; S1800 series photoresist; NaOH (particles or solution).

[0110] First, perform the general photoresist process described below. Then mix the Ag etching solution. Add 75 mL of 3% USP-grade H₂O₂ to the crystallizing dish, followed by 8 mL of lab-grade 30% ammonium hydroxide. Immerse the patterned substrate in the solution for 30 seconds, stirring gently. Bubbles may not form when the reaction is complete. Rinse with DI water, then dry with nitrogen or argon. Remove the photoresist with 0.3M NaOH solution.

[0111] Gold patterning, sputtering and stripping

[0112] Objective: To pattern Au pads on a Ti / PI / Ag substrate. Materials included: a 50 x 75 mm silver-sputtered Ti / PI substrate on a glass slide; NaOH microspheres; a 300 mL beaker; a 250 mL beaker; an optical mask; S1813 primers; Ti / PI / glass substrate with Ag deposited on the surface; 80 / 20 primers, as described in detail above; an Ag etching mask; a 3 mL pipette; acetone; isopropanol (IPA); a crystallizing dish; a graduated cylinder; and a timer.

[0113] Perform the general photoresist process described below. Clean under Ar for 1 minute. Start the vacuum system. Sputter 90 nm (0.900 kA) Pt. Sputter 50–90 nm Au (density = 19.3, Z-ratio = 0.381). Completely cover the substrate with Scotch tape. Press firmly down on the substrate and then slowly remove to remove the Au layer. Check the tape test piece for Au adhesion failure. Use an additional strip of tape to remove any bridging between the Au pads. Remove the photoresist / remaining Pt / Au using the tape method (3 m Magic tape over the entire array), then sonicate in 0.5 M NaOH. If bridging residue remains, gently scrub with Kimwipe in the solution.

[0114] Titanium etching (removing unwanted titanium to form electrical interconnects)

[0115] Objective: To define and isolate titanium traces on the sensor. It is important to prevent titanium beneath the indicator electrode or indicator electrode interconnect trace from contacting titanium beneath other indicator electrodes / traces or the titanium beneath the reference electrode / traces. Materials include Ti / Pi mounting slides; titanium etchant; 400mL beakers; crystallizing dishes; DI water; NaOH; and ultrasonic cleaner.

[0116] Perform the general photoresist process described below. Prepare the etching tank. Place the substrate in the etchant solution and observe carefully. After etching, rinse with DI water.

[0117] Rinse with DI water, then dry with nitrogen or argon.

[0118] Fabrication of a sensor for human use: personalization, encapsulation, chlorination, application of a protective coating to the reference electrode, and cleaning. Indicator electrode

[0119] Each trielectrode strip can be personalized using mechanical or photonic technologies such as UV lasers (wavelength: 405nm).

[0120] Wrap the electrode strip around a 21-25 gauge stainless steel needle (with a sharp bevel at the end) or a blunt tube. Wrap the electrode strip axially around the needle / tube and secure it with epoxy resin or another biocompatible adhesive. If using a blunt tube, use a sharp needle inside the tube to pierce the skin upon insertion. (The needle is then removed, allowing medication to be delivered through the lumen of the tube).

[0121] Chlorinate iron with 50mM FeCl3 for 5-10 minutes. Alternative: Electrochlorinate using a power supply configured at 0.6V for 10 minutes, with Ag as the anode (+) and Pt as the cathode (-). The bath used for electrolytic chlorination is 0.5M KCl and HCl.

[0122] Voltage cycling (cleaning) of the indicator electrode in 1x PBS: -1.5V x 5 min, 1.5V x 5 min, -1.5V x 5 min. Verify the presence of released air bubbles at the electrode location.

[0123] Redox mediator polymers and glucose oxidase are applied to the surface of a gold indicator electrode. In this embodiment, the redox mediator polymer listed is poly-(1-vinyl)-imidazolium-MRMMG-4,4'-dimethyl-2,2'-bipyridine. However, compounds with pyridine- or imidazolium-based MRMMG ligands and polyvinylpyridine, polyvinylimidazolium, or other polymers as a backbone can also be used. Another metal (such as ruthenium, iridium, iron, or cobalt) can replace osmium to produce similar results.

[0124] Before this step begins, the gold triple electrode has been wrapped, cleaned, and chlorinated.

[0125] Using DIW as the solvent, prepare two solutions in less than 1 mL each: a redox mediator polymer (10 mg / mL) and glucose oxidase, 100 units per mg (10 mg / mL). Combine 40 μL of the redox mediator solution and 10 μL of the glucose oxidase solution. When dispensing manually, use a 30-gauge needle to draw the mixture into a 1 mL plastic syringe, carefully placing the needle tip at 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.

[0126] Place the support upright in a glutaraldehyde vapor chamber (25% glutaraldehyde) for 30 minutes, then cure at room temperature for 30 minutes.

[0127] The outer membrane deposited across the entire axis, including the indicator and reference electrodes, can be one of many glucose-permeable polymers, including polyurethane, siloxane, combined siloxane-polyurethane, or other polymers. An effective outer membrane is a poly(4-vinyl or 2-vinyl)pyridine-styrene copolymer (10-30% styrene, PVP-S) at 64 mg / ml in anhydrous ethanol. This polymer can be deposited manually using an automated dip-coating machine, an inkjet printer, microcontact printing, or other precise dispensing methods. Coat the entire sensor axis with the outer membrane material. Allow to dry at room temperature for 15 minutes.

[0128] After drying, the sensor can be tested in solutions such as glucose and interfering compounds.

[0129] Assembled into an electronic module, which is used for telemetry and polarization bias applications.

[0130] Insert the sensor tube into a battery-powered telemetry module (e.g., a low-energy Bluetooth module sold by Nordic, Inc.).

[0131] For the redox mediator polymer method discussed above, a potential bias of 180 mV is suitable. This low bias largely avoids signal artifacts caused by the oxidation of insulin preservatives (phenol, m-cresol), which would occur with higher biases. The low bias also avoids the electropolymerization problems that typically occur with higher bias potentials. With higher bias potentials, cresol and / or phenol undergo electropolymerization, depositing a viscous layer of insulating plastic on the electrode. This plastic layer reduces or eliminates the connectivity between the redox mediator metal group members and the electrode material, and also reduces the transport of molecules such as hydrogen peroxide to the indicator electrode surface.

[0132] sterilization

[0133] Exposure to electron beams, gamma rays, ethylene oxide, or activated glutaraldehyde sterilization solutions.

[0134] Attach to and operate the insulin pump

[0135] After insulin infusion, an infusion line from an insulin pump (e.g., Medtronic Minimed, Animas Ping, Tandemt-slim, Roche Spirit, etc.) is attached to a sensing catheter (located in the subcutaneous tissue) to deliver insulin. A constant pressure head from the fluid infusion line prevents backflow of fluid from the body. For display to the user, glucose concentration, or current or voltage data representing glucose concentration, is obtained from the sensor. This data is 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 on any of these devices or on a body-worn electronic device directly connected to the subcutaneous sensing catheter. The advantage of storing glucose data on a body-worn device is that data is not lost if the receiving device is lost or out of range.

[0136] Universal photoresist process (shared across multiple steps)

[0137] Materials: 50 x 75 mm Ti / PI substrate on a glass slide; NaOH particles or solution; 300 mL beaker; 250 mL beaker; optical mask; photoresist; 80 / 20 primers, as defined above.

[0138] Method: Mix 200 ml of 0.1 M NaOH (8 g / L granules or 15 mL / L 10 M solution) as the primary developer in a glass dish. Ensure the solution is thoroughly mixed, especially when using NaOH granules. Mix 0.075 M NaOH as a secondary rinse solution in the glass dish. Ensure the solution is thoroughly mixed. Spin-coat 3 mL of 80 / 20 primer at 1000 RPM for 10 seconds, then at 3000 RPM for 30 seconds using the standard method. Bake at 85°C for 3 minutes. Spin-coat three layers of photoresist using the standard method. Between each spin-coat step, bake the substrate at 85°C for 1 minute. Expose at 600 W for 180 seconds. Bake for another 60 seconds. Develop in 0.1 M NaOH developer, stirring gently. Rinse in the secondary bath for 10 seconds. Dry with nitrogen and check for any areas with residual resist in the developed area. (The exposed area should be uniform across the entire substrate. If no photoresist residue remains on the surface, properly cleaned areas may show a faint white appearance as they dry from wet). Bake for 10 minutes and allow to cool. If areas remain, soak in the main and secondary baths for 5 seconds, then check again. If a large area remains, air dry, wash with 0.3M NaOH, then return to step 4. Check the process parameters.

[0139] Example 2: Filtering using a platinum indicator electrode with a high bias potential

[0140] Many aspects of this embodiment are the same as those of Embodiment 1. However, instead of depositing Au, Pt is deposited by sputtering using these sputtering devices: density = 10.5, Z ratio = 0.529.

[0141] No redox mediator was used. Glucose oxidase was used in conjunction with the protein elongation agent bovine serum albumin. Glutaraldehyde crosslinking agent was used to link the amino groups of glucose oxidase and albumin, with a weight ratio of glucose oxidase:albumin:liquid glutaraldehyde between 6:4:5 and 6:4:1. The mixture applied to the Pt electrode was dried at 40°C for at least 10 minutes. An additional layer may be deposited to increase glucose sensitivity. In such cases, the final coating was dried for at least 20 minutes. It was then rinsed in a stirred DIW for 10–15 minutes to remove unbound enzyme. Two outer membranes consisting of 1.5–2.5% w / v polyurethane (PU) or a copolymer of siloxane and polyurethane were deposited on the indicator and reference electrodes. Such polymers are manufactured by suppliers such as AdvanSource Biomaterials, Lubrizol, or DSM Polymers. The proportion of siloxane was used to adjust oxygen permeation; and the polyethylene oxide or polyethylene glycol portion or other polar portion was used to adjust glucose permeation. A suitable solvent is a mixture of THF and DMAC (25:75, v / v). Dry each PU coating at 40°C for 20 minutes. Use a 3A or 4A molecular sieve to retain the solvent and polymer / solvent for drying.

[0142] The suitable material for the filter is Sephadex G10, which is rated to separate compounds with molecular weights greater than 700 Da from those with molecular weights less than 700 Da. A suitable tubular structure with an inner diameter of approximately 3 mm and an internal length of at least 64 mm is filled with Sephadex G10 beads of 40-120 μm in size. The filter is placed in the fluid path of the insulin formulation. The distal end of the filter is surrounded by a porous cellulose acetate membrane to prevent Sephadex gel from entering the fluid path and being delivered to the patient. The cellulose acetate has a pore size of 0.22 μm. Ideally, the filter beads are exposed to an aqueous buffer, such as phosphate buffer, to allow them to swell before the insulin formulation is added to the filter.

[0143] While preferred embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided by way of example only. The invention is not limited to the specific examples provided in the specification. Although the invention has been described with reference to the foregoing specification, the description and illustrations of embodiments herein are not intended to be limiting. Many variations, modifications, and substitutions will now occur to those skilled in the art without departing from the invention. Furthermore, it should be understood that all aspects of the invention are not limited to the specific descriptions, configurations, or relative proportions set forth herein, and depend on various conditions and variables. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in the practice of the invention. Therefore, the invention is intended to also cover any such alternatives, modifications, variations, or equivalents. The following claims are intended to define the scope of the invention and thereby cover the methods and structures within the scope of these claims and their equivalents.

Claims

1. A device for delivering insulin or insulin analog formulations and measuring subcutaneous glucose concentration, the device comprising: A hollow tube comprising a proximal end and a distal end, wherein the proximal end is in fluid communication with a source of the insulin or insulin analog formulation, wherein the distal end is configured for subcutaneous delivery of the insulin or insulin analog formulation, wherein the insulin or insulin analog formulation comprises an excipient, the excipient comprising phenol or cresol. and A current-type glucose sensor located at a distance not exceeding a predetermined distance from the distal end, wherein the current-type glucose sensor includes: An electrode layer comprising at least one indicator electrode, wherein the electrode layer is located beneath a redox catalytic layer, the redox catalytic layer comprising: (1) a redox mediator comprising a metal compound covalently bound to a ligand, wherein the ligand is pyridine-based or imidazole-based, wherein the metal compound comprises a metal selected from ruthenium, palladium, platinum, rhodium, iridium, cobalt, iron, and copper; and (2) an enzyme comprising glucose oxidase or glucose dehydrogenase. The redox mediator and the enzyme allow electrons to transfer from subcutaneous glucose to the at least one indicating electrode, and this electron transfer is sufficient to cause the current-type glucose sensor to respond to the subcutaneous glucose concentration at an applied bias potential not exceeding +250 mV relative to a reference electrode. The applied bias potential, which is no more than +250 mV relative to the reference electrode, allows the electrode layer to avoid undergoing electropolymerization of the excipient during at least one hour of continuous operation of the current-type glucose sensor, thereby maintaining the sensitivity of the current-type glucose sensor to the subcutaneous glucose concentration in the presence of the insulin or insulin analog formulation.

2. The device of claim 1, further comprising a housing including an upper accessible surface and a lower surface configured for adhesion to a skin surface.

3. The device of claim 1, wherein the current-type glucose sensor is disposed on a second hollow tube including a second distal end, wherein the second distal end is configured for subcutaneous insertion.

4. The apparatus of claim 1, wherein the at least one indicating electrode comprises gold, carbon, platinum or iridium.

5. The apparatus of claim 1, wherein the at least one indicating electrode comprises graphite.

6. The device according to claim 1, wherein the ligand is 4,4'-dimethyl-2,2'-bipyridine.

7. The apparatus of claim 1, wherein the redox mediator is combined with poly(4-vinylpyridine).

8. The apparatus of claim 1, wherein the redox mediator is combined with poly(1-vinylimidazole).

9. The apparatus according to claim 1, wherein the predetermined distance is 15 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.

10. The apparatus of claim 1, wherein the current-type glucose sensor further comprises a reference electrode.

11. The apparatus of claim 10, wherein the reference electrode comprises a silver / silver chloride reference electrode.

12. The device of claim 1, wherein the current-type glucose 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.

13. The apparatus of claim 12, wherein the insulating layer comprises polyimide or liquid crystal polymer.

14. The apparatus of claim 12, wherein the metal layer has a thickness of at least 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

15. The apparatus of claim 14, wherein the metal layer comprises titanium, gold, or platinum.

16. The apparatus of claim 1, wherein the electrode layer comprises a film with a thickness not exceeding 1000 nm, 900 nm, 800 nm, 700 nm, 600 nm, 500 nm, 400 nm, 300 nm, 200 nm or 100 nm.

17. The device of claim 1, wherein the redox mediator and the enzyme allow electrons to transfer from subcutaneous glucose to the at least one indicating electrode, the electron transfer being sufficient to cause the current-type glucose sensor to respond to subcutaneous glucose concentration at an applied bias potential not exceeding +200 mV, +150 mV, +100 mV, or +50 mV relative to a reference electrode.

18. The device of claim 17, wherein the applied bias potential, relative to the reference electrode, is no more than +200 mV, +150 mV, +100 mV, or +50 mV, allowing the electrode layer not to undergo electropolymerization of the excipient during at least one hour of continuous operation of the current-type glucose sensor, thereby maintaining the sensitivity of the current-type glucose sensor to the subcutaneous glucose concentration in the presence of the insulin or insulin analog formulation.

19. The apparatus according to any one of claims 1 to 18, wherein the ligand comprises a pyridine ring bound to an imidazole ring, a non-nitrogen element substituted into a heterocycle, or an associated "R" group bound to a heterocycle.

20. The apparatus of claim 1, wherein the apparatus is used to perform a method for measuring subcutaneous glucose concentration during subcutaneous delivery of insulin or an insulin analog formulation, the method comprising: ‎ (a) Obtaining an apparatus for measuring subcutaneous glucose concentration during subcutaneous delivery of the insulin or insulin analog formulation; (b) Connecting the proximal end of the hollow tube to the source of the insulin or insulin analog formulation; (c) The distal end of the hollow tube is subcutaneously inserted into the body of the subject; and (d) During subcutaneous delivery of the insulin or insulin analog formulation, the subcutaneous glucose concentration of the subject is measured.

21. The apparatus of claim 20, wherein the subject suffers from type 1 diabetes.

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