CN112088217A

CN112088217A - Thermostable glucose limiting membrane for glucose sensors

Info

Publication number: CN112088217A
Application number: CN201980030243.0A
Authority: CN
Inventors: 振汉·拉里·王; 德洛·哈威纳斯; 普纳姆·S·古拉蒂
Original assignee: Medtronic Minimed Inc
Current assignee: Medtronic Minimed Inc
Priority date: 2018-05-16
Filing date: 2019-05-16
Publication date: 2020-12-15
Also published as: WO2019222499A1; EP3794135A1; CA3100384A1

Abstract

Embodiments of the invention provide compositions useful in analyte sensors and methods for making and using such compositions and sensors. In typical embodiments of the present invention, the sensor is a glucose sensor that includes an analyte modulating membrane formed from a polymerization reaction mixture formed to include a limited amount of catalyst and/or polycarbonate compound to provide such membranes with improved material properties, such as enhanced thermal and hydrolytic stability.

Description

Thermostable glucose limiting membrane for glucose sensors

Cross reference to related applications

The present application claims priority from U.S. patent application serial No. 15/981,681 entitled "thermally stable glucose limiting membrane for glucose sensor (THERMALLY STABLE GLUCOSE LIMITING MEMBRANE FOR GLUCOSE SENSORS)" filed on 2018, 5/16, according to section 120, the contents of which are incorporated herein by reference.

Technical Field

The present invention relates to biosensors such as glucose sensors for diabetes management and materials for making such sensors, e.g., polymeric compositions useful for biosensor membranes.

Background

Analyte sensors, such as biosensors, include a means for converting a chemical analyte in a matrix to a detectable signal using a biological element. There are many types of biosensors used to detect a wide variety of analytes. Perhaps the most studied type of biosensor is the amperometric glucose sensor, a device commonly used to monitor glucose levels in individuals with diabetes.

A typical glucose sensor works according to the following chemical reaction:

H₂O₂→O₂+2H⁺+2e^-equation 2

Glucose oxidase is used to catalyze the reaction between glucose and oxygen to produce gluconic acid and hydrogen peroxide as shown in equation 1. H₂O₂An electrochemical reaction occurs as shown in equation 2, and the current is measured by a potentiostat. The stoichiometry of the reaction presents challenges for developing sensors in vivo. In particular, for optimal sensor performance, the sensor signal output should be determined only by the analyte of interest (glucose), and not by any co-matrix (O)₂) Or kinetic control parameters such as diffusion. If oxygen and glucose are presentIn equimolar concentration, then H ₂0₂Stoichiometrically related to the amount of glucose reacted at the enzyme; and the associated current that generates the sensor signal is proportional to the amount of glucose reacted with the enzyme. However, if there is insufficient oxygen to react all of the glucose with the enzyme, the current will be proportional to the oxygen concentration rather than to the glucose concentration. Thus, in order for the sensor to provide a signal that depends only on the glucose concentration, glucose must be the limiting reagent, i.e. 0₂The concentration must exceed all potential glucose concentrations. However, a problem with using such glucose sensors in vivo is that the oxygen concentration at the time of implantation of the sensor in vivo is low relative to glucose, a phenomenon that can compromise the accuracy of the sensor readings.

There are many approaches to solving the problem of hypoxia. One approach is to use a homogeneous polymer membrane with hydrophobic and hydrophilic regions that control oxygen and glucose permeability. For example, Van Antwerp et al developed linear polyurea membranes comprising polyethylene glycol and silicone hydrophobic components that allow high oxygen permeability in combination with hydrophilic components that allow limited glucose permeability (see, e.g., U.S. patent nos. 5,777,060, 5,882,494, and 6,642,015). While having many useful and desirable properties, such polymeric compositions may exhibit some degradation over time under conditions of high temperature and high humidity. In view of this, there is a need in the art for more robust polymeric membrane compositions that can be used, for example, to address the problem of oxygen deficiency observed in glucose sensors that incorporate glucose oxidase.

Disclosure of Invention

Embodiments of the invention provide compositions useful in analyte sensors and methods for making and using such compositions and sensors. In typical embodiments of the invention, the sensor is a glucose sensor that includes an analyte modulating membrane formed from a polymerization reaction mixture that includes a limited amount of a catalyst to provide improved material properties, such as enhanced thermal and hydrolytic stability, to such membranes. As disclosed herein, when these polymer compositions are used to form analyte limiting membranes in glucose sensors, the resulting sensors exhibit enhanced long term stability profiles as compared to conventional polymer compositions formed from reaction mixtures using conventional amounts of catalysts.

The invention disclosed herein has many embodiments. One embodiment of the present invention is a method of increasing the thermal stability of a biocompatible film formed from a reaction mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst. In this method, the reaction mixture is formed such that the catalyst is present in the reaction mixture in an amount less than 0.2% of the reaction mixture components (e.g., 0.1%), thereby increasing the thermal stability of the biocompatible membrane as compared to a comparable membrane formed from the reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture. Optionally, the reaction mixture further comprises additional components, such as a polycarbonate diol.

Another embodiment of the invention is an amperometric detection analyte sensor comprising: a base layer; a conductive layer disposed on the base layer and comprising a working electrode; an analyte sensing layer disposed on the conductive layer; and an analyte modulation layer disposed on the analyte sensing layer. In this embodiment, the analyte modulating layer is formed from a reaction mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst. In this embodiment, the catalyst is present in the reaction mixture in an amount less than 0.2% of the reaction mixture components such that the analyte modulating layer exhibits greater thermal stability than a comparable analyte modulating layer formed from the reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture.

Yet another embodiment of the present invention is a method of making an analyte sensor for implantation in a mammal. This method embodiment comprises the steps of: providing a base layer; forming a conductive layer on the base layer, wherein the conductive layer includes a working electrode; forming an analyte sensing layer on the conductive layer, wherein the analyte sensing layer comprises an oxidoreductase; and then forming an analyte modulation layer on the analyte sensing layer. In this embodiment, the analyte modulating layer is formed from a reaction mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst present in the reaction mixture in an amount less than 0.2% of a reaction mixture component (e.g., 0.1%), such that the reaction mixture exhibits greater thermal stability as compared to a comparable analyte modulating layer formed from the reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture. Optionally, the reaction mixture further comprises additional components, such as a polycarbonate diol.

Other objects, features and advantages of the present invention will become apparent to those skilled in the art from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating some embodiments of the present invention, are given by way of illustration and not limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

Drawings

Referring now to the drawings in which like reference numbers represent corresponding parts throughout:

FIG. 1 provides a diagrammatic view of one embodiment of an amperometric detection analyte sensor having multiple layered materials/elements in accordance with one or more embodiments of the present invention;

fig. 2A-C show the chemical structure of raw materials used in a polycarbonate urea glucose-limiting membrane (GLM) according to one or more embodiments of the invention. Fig. 2A shows the chemical structures of PDMS and Jeffamine. FIG. 2B shows 4,4 '-methylenebis (cyclohexyl isocyanate) or HMDI and 4,4' -methylenebis (phenyl isocyanate) or MDI. FIG. 2C shows the chemical structure of a polycarbonate diol;

FIG. 3 illustrates a GLM synthesis reaction according to one or more embodiments of the present invention;

fig. 4A-B illustrate various counter electrode morphologies compared to the morphology of the working electrode after testing in accordance with one or more embodiments of the present invention. Fig. 10A shows bubbles (or pits) generated at the counter electrode after use. The formation of bubbles at the electrodes may trigger delamination or unwanted biological responses (due to texture changes or rough surfaces). Fig. 10B shows that MDI _ polycarbonate _ GLM can enhance GLM adhesion such that no bubbles (or craters) are generated at the counter electrode after use;

FIG. 5 shows in vitro SITS data comparison between standard 2xGLM and PCU _ GLM (polycarbonate urea glucose limiting membrane) according to one or more embodiments of the present invention;

FIG. 6 shows an E3 sensor morphology after 7-day SITS testing on a standard 2XGLM coated sensor and a PCU _ GLM coated sensor in accordance with one or more embodiments of the invention;

figures 7A-B provide graphs of data from thermal degradation studies for various formulations and compositions of the formulations. Fig. 7A provides results from a thermal degradation study comparing the degradation (as observed by molecular weight reduction) of polymeric materials useful as biocompatible membranes (e.g., analyte modulating layers in glucose sensors) at 45 ℃, while fig. 7B provides results from a similar thermal degradation study conducted at 60 ℃. In fig. 7A and 7B, the "control" material is formed from the polymerization mixture, where the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the polymerization mixture, and the "new" material is formed from the polymerization mixture, where the catalyst is present in the formulation in an amount less than 0.2% of the reaction mixture (0.1% in this case).

Fig. 8A-E show results from thermal degradation studies for various formulations and compositions of formulations, in accordance with one or more embodiments of the present invention. Fig. 8A shows results from a thermal degradation study. Fig. 8B-D show the composition of various formulations. FIG. 8E provides data showing that the glucose permeability (Pg) of polycarbonate _ GLM is not reduced after baking;

fig. 9 shows a summary of results from thermal/hydrolysis studies of various sample formulations, according to one or more embodiments of the invention. The thermal degradation test results demonstrate that MDI and polycarbonate chains can contribute to (slow) the GLM degradation process.

Detailed Description

Unless defined otherwise, all technical terms, symbols, and other scientific terms or terminology used herein are intended to have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In some instances, terms having commonly understood meanings are defined herein for clarity and/or ease of reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is commonly understood in the art. Those skilled in the art will readily understand and generally employ many of the techniques and procedures described or referenced herein using routine methodology. Procedures involving the use of commercially available kits and reagents were generally performed according to manufacturer-defined protocols and/or parameters, as desired, unless otherwise indicated. A number of terms are defined below. All publications mentioned herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The publications cited herein are incorporated by reference for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such publication by virtue of an earlier priority date or priority date of invention. Further, the actual publication date may be different from that shown and require independent verification.

It must be noted that, as used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "an oxidoreductase" includes a plurality of such oxidoreductases and equivalents thereof known to those skilled in the art, and so forth. All numbers recited in the specification and associated claims referring to a value that can be numerically characterized with a value other than an integer (e.g., "50 mol%") are to be understood as modified by the term "about".

The term "analyte" as used herein is a broad term and is used in its ordinary sense, including but not limited to referring to a substance or chemical constituent in a fluid such as a biological fluid (e.g., blood, interstitial fluid, cerebrospinal fluid, lymph or urine) that can be analyzed. The analyte may comprise a naturally occurring substance, an artificial substance, a metabolite, and/or a reaction product. In some embodiments, the analyte for measurement by the sensing regions, devices, and methods is glucose. However, other analytes are also contemplated, including but not limited to lactate. In certain embodiments, salts, sugars, proteins, fats, vitamins, and hormones naturally present in blood or interstitial fluid may constitute the analyte. The analyte may be naturally present in the biological fluid or endogenous; for example, metabolites, hormones, antigens, antibodies, and the like. Alternatively, the analyte may be introduced into the body or be exogenous, for example, a contrast agent for imaging, a radioisotope, a chemical agent, fluorocarbon-based synthetic blood, or a drug or pharmaceutical composition, including but not limited to insulin. Metabolites of drugs and pharmaceutical compositions are also contemplated analytes.

The term "sensor" as used herein is a broad term and is used in its ordinary sense, including, but not limited to, one or more portions of an analyte monitoring device that detect an analyte. In one embodiment, the sensor comprises an electrochemical cell having a working electrode, a reference electrode, and optionally a counter electrode that passes through the sensor body and is fixed within the sensor body, thereby forming an electrochemically reactive surface at one location on the body, forming an electrical connection at another location of the body, and forming a membrane system that is adhered to the body and covers the electrochemically reactive surface. During the general operation of the sensor, a biological sample (e.g., blood or interstitial fluid) or a portion thereof is contacted with an enzyme (e.g., glucose oxidase) (either directly or after passing through one or more membranes or domains); the reaction of the biological sample (or a portion thereof) results in the formation of a reaction product that allows the determination of the analyte level in the biological sample.

As discussed in detail below, embodiments of the present invention relate to the use of electrochemical sensors exhibiting a novel array of material and functional elements. Such sensors incorporate new polymeric compositions to form robust analyte modulating membranes having a unique set of technically desirable material properties, such as increased thermal stability. The electrochemical sensors of the present invention are designed to measure an analyte of interest (e.g., glucose) or a concentration of a substance present or the concentration of an analyte in an indicator fluid. In some embodiments, the sensor is a continuous device, such as a subcutaneous, percutaneous, or intravascular device. In some embodiments, the device may analyze a plurality of intermittent blood samples. The sensor embodiments disclosed herein may use any known method, including invasive, minimally invasive, and non-invasive sensing techniques, to provide an output signal indicative of the concentration of the analyte of interest. Typically, the sensor is of the type that senses the product or reactant of an enzymatic reaction between an analyte and an enzyme in the presence of oxygen as a measure of the analyte in vivo or in vitro. Such sensors include a polymeric membrane surrounding the enzyme through which the analyte migrates prior to reaction with the enzyme. The product is then measured using electrochemical methods, and thus the output of the electrode system serves as a measure of the analyte. In some embodiments, the sensor may use amperometric, coulometric, conductometric, and/or potentiometric techniques to measure the analyte.

Analyte modulating compositions (such as those that can be used as glucose limiting membranes in amperometric detection glucose sensors) include polymeric compositions formed from biocompatible polyurea materials (see, e.g., the context of biocompatible polyurea materials incorporated by reference). Such compositions may exhibit stable glucose and oxygen permeability, low protein adsorption rates, and biocompatibility. However, due to the content of PEG chains, certain degradation problems may occur under high temperature conditions and/or high humidity conditions. As disclosed in detail below, we have found that certain carbonate and aromatic isocyanate compounds can be added to the polymerization reaction to replace some portion of the polymeric chain elements of PDMS and HMDI. Two compounds have been found to increase the heat resistance and hydrolysis resistance of these polymers under high temperature and high humidity conditions. In addition, the chemical structure of the compounds provides evidence that such compositions have very good e-beam resistance. Carbonate materials that may be used in embodiments of the present invention include, but are not limited to, polycarbonate diols (e.g., butanediol or hexanediol or similar compounds). In an illustrative embodiment of the invention, the carbonate material has a Mw of 500 to 2000 daltons. Aromatic isocyanate materials that may be used in embodiments of the present invention include, but are not limited to, MDI or similar compounds.

In addition to the limited amount of catalyst in the polymerization reaction mixture, the addition of MDI can improve the heat resistance and electron beam resistance of the polymeric composition used as an analyte modulating (e.g., glucose limiting) composition by its benzene ring structure. The benzene ring also acts as a good radical scavenger for preventing oxidation of the polymer component. Polycarbonate diols can provide better heat resistance and hydrolysis resistance through their carbonate structure (relative to ether or ester chains). The addition of polycarbonate segments in the polymer backbone can prevent unwanted deformation of the polymer composition layer disposed on the electrodes of the amperometric detection glucose sensor. Both gas and water are generated on the counter electrode between the analyte sensing layer (e.g. one containing an enzyme such as GOX) and the analyte modulating (e.g. glucose limiting membrane) layer, which may lead to sensor failure (signal drift) after prolonged use. In this case, the polycarbonate segments in the GLM backbone can prevent/reduce chain rotation of PDMS in the GLM film, so the glucose permeability (Pg) of GLM does not gradually decrease over time, since hydrophilic chains (Jeffamine or PEG) are wrapped/enclosed by hydrophobic PDMS chains, especially for low Pg GLM. In certain embodiments, to make a homogeneous urethane/urea copolymer, the synthesis will involve 3 raw material injections after different timings. The raw materials were injected at a rate of 4-2-4 at times of 0, 4, and 12 hours, respectively. The addition of polycarbonate chains in GLM can prevent the variation/decrease in Pg due to rotation/entanglement of PDMS chains over time, especially for low Pg GLM films. To reduce thermal/radiation/oxidative degradation, the desired MDI content in the final polymer may be 2% to 25%. To prevent film deformation or Pg reduction due to rotation of the silicone chains over time, the desired polycarbonate content in the final polymer may be 8% to 30%. Polycarbonate GLM showed good adhesion to AP and no more craters (bubbles) were formed after the test.

Embodiments of the invention disclosed herein provide sensor types for subcutaneous or transcutaneous monitoring of blood glucose levels in diabetic patients, for example. Various implantable electrochemical biosensors have been developed to treat diabetes and other life-threatening diseases. Many existing sensor designs use some form of immobilized enzyme to achieve their biospecificity. Embodiments of the invention described herein may be adapted and implemented using a variety of known electrochemical sensors, including, for example, U.S. patent application No. 20050115832, U.S. patent nos. 6,001,067, 6,702,857, 6,212,416, 6,119,028, 6,400,974, 6,595,919, 4,703,756, 6,595,919, 5,391,250, 5,482,473, 6,595,919, WO 6,595,919, WO 08/042625 and WO 03/074107, and european patent application EP 1153571, the contents of each of which are incorporated herein by reference.

As discussed in detail below, embodiments of the invention disclosed herein provide sensor elements having enhanced material properties and/or architectural configurations and sensor systems (e.g., sensor systems including a sensor and associated electronic components such as a monitor, processor, etc.) configured to contain such elements. The present disclosure further provides methods for making and using such sensors and/or architectural configurations. While some embodiments of the present invention relate to glucose sensors and/or lactate sensors, the various elements disclosed herein (e.g., an analyte modulating membrane made from a polycarbonate polymeric composition) may be adapted for use with any of a wide variety of sensors known in the art. Analyte sensor elements, architectures, and methods for making and using these elements disclosed herein can be used to create a variety of layered sensor structures. Such sensors of the present invention exhibit a surprising degree of flexibility and versatility, allowing a wide variety of sensor configurations to be designed to examine the characteristics of a wide variety of analyte species.

Specific aspects of embodiments of the invention are discussed in detail in the following sections.

Exemplary elements, configurations and analyte sensors of the invention

Optimized sensor element of the invention

A wide variety of sensors and sensor elements are known in the art including amperometric detection sensors for detecting and/or measuring biological analytes such as glucose. Many glucose sensors are based on oxygen (Clark-type) amperometric detection transducers (see, e.g., Yang et al, electronic analysis (Electroanalysis) 1997,9, 16: 1252- & 1256; Clark et al, Ann.N.Y., academy of

sciences

1962,102, 29; Updike et al, Nature 1967,214,986; and Wilkins et al, medical engineering and Physics 1996,18,273.3-51). Many in vivo glucose sensors utilize hydrogen peroxide-based amperometric detection transducers because the transducers are relatively easy to manufacture and can be readily made small using conventional techniquesAnd (4) forming. However, one problem associated with the use of certain amperometric detection transducers involves suboptimal reaction stoichiometry. As discussed in detail below, these problems are addressed by the use of one or more polycarbonate polymeric membranes disclosed herein that can modulate the transmission characteristics of different compounds whose reaction produces a signal at a hydrogen peroxide-based amperometric detection transducer element. Thus, these membranes can be used with, for example, various H-based membranes₂O₂Analyte sensors that benefit from optimized reaction stoichiometry are used together.

As noted above, embodiments of the present invention comprise a sensor film made from a reaction mixture to contain a limited amount of catalyst and/or polycarbonate polymer composition. As is known in the art, polymers comprise long molecules or larger molecules consisting of a chain or network of many repeating units formed by chemically bonding together many identical or similar small molecules called monomers. A copolymer or heteropolymer is a polymer derived from two (or more) monomer species, as opposed to a homopolymer where only one monomer is used. Copolymers may also be described in terms of the presence or arrangement of branches in the polymer structure. Linear copolymers consist of a single backbone, while branched copolymers consist of a single backbone and one or more polymeric side chains. Sensor membranes made from the polycarbonate polymeric compositions disclosed herein can optimize analyte sensor functions including sensor sensitivity, stability, and hydration profile. In addition, by optimizing the stoichiometry of a reactant species over a range of sensor temperatures, the membranes disclosed herein can optimize chemical reactions that produce key measurable signals related to analyte (e.g., glucose) levels of interest. The following sections describe illustrative sensor element, sensor configuration, and method embodiments of the invention.

The polymeric materials disclosed herein can be used in various circumstances as biocompatible membranes, for example as Glucose Limiting Membranes (GLM). However, polymers typically degrade over time due to oxidation, UV light, heat, hydrolysis, or other processes. In this case, it has been found that trace amounts of tin catalyst residues in polymer mixtures used to form biocompatible films such as GLM can accelerate GLM degradation over time. For this reason, older sensors may perform slightly worse than newly manufactured sensors due to the gradual degradation of GLM. While not being bound by a particular scientific theory or mechanism of action, it is believed that trace amounts of tin catalyst residues in GLM may further trigger immune reactions and loss of sensitivity. In this case, it was further found that reducing the amount of tin catalyst used during GLM synthesis (e.g., by 50%) unexpectedly produced a film with increased resistance to thermal degradation and improved GLM quality (biocompatibility and thermal stability) as well as glucose sensor in vivo performance. This greater GLM stability further extends the shelf life of the sensor and improves the biocompatibility of the sensor without any significant manufacturing process variations.

The invention disclosed herein has many embodiments. One embodiment of the present invention is a method of increasing the thermal stability of a biocompatible film formed from a reaction mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst. In this method, the reaction mixture is formed such that the catalyst is present in the reaction mixture in an amount less than 0.2% of the reaction mixture components (e.g., 0.1%), thereby increasing the thermal stability of the biocompatible membrane as compared to a comparable membrane formed from the reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture. Optionally, the reaction mixture (e.g., at 60 ℃) uses an organic solvent such as tetrahydrofuran and further includes additional components such as polycarbonate diol. The thermal stability of various biocompatible films fabricated in this manner can be measured by various prior art accepted practices, for example by observing the change in molecular weight of the biocompatible film during maintenance at a temperature of 60 ℃ for at least 3 days, 5 days, or 7 days (see, e.g., fig. 7).

In certain embodiments of the invention, a tin catalyst (e.g., dibutyltin bis (ethyl 2-hexanoate)) is present in the reaction mixture in an amount less than 0.19%, 0.17%, 0.15%, 0.13%, or 0.11% of the reaction mixture (e.g., 0.1%). In some embodiments of the invention, the diisocyanate comprises hexamethylene diisocyanate and/or methylene diphenyl diisocyanate, and/or the hydrophilic polymer comprising a hydrophilic diol or hydrophilic diamine comprises JEFFAMINE, and/or the siloxane having amino, hydroxyl or carboxylic acid functional groups at the termini comprises polydimethylsiloxane, and/or the polycarbonate diol comprises poly (1, 6-hexyl carbonate) diol and/or poly (1, 6-hexyl-1, 5-pentyl carbonate) diol. For example, in certain embodiments of the present invention, the diisocyanate comprises 17 to 23 weight percent hexamethylene diisocyanate and 0 to 8.5 weight percent methylene diphenyl diisocyanate, and the JEFFAMINE comprises 28 to 51 weight percent JEFFAMINE 600 and/or JEFFAMINE 900, and the polydimethylsiloxane comprises 14 to 48 weight percent polydimethylsiloxane-a 15, and the polycarbonate diol comprises 7.5 to 19 weight percent poly (1, 6-hexyl carbonate) diol. In a particular illustrative embodiment, the diisocyanate comprises about 22% hexamethylene diisocyanate and about 3.5% methylene diphenyl diisocyanate, the JEFFAMINE comprises about 45% JEFFAMINE 600 and/or JEFFAMINE 900, the polydimethylsiloxane comprises about 22.5% polydimethylsiloxane-a 15, and the polycarbonate diol comprises about 7.5% poly (1, 6-hexyl carbonate) diol. Optionally, in this process, water is added as a chain extender to the reaction mixture of the polyurea-polyurethane copolymer. Illustrative reaction mixtures of the present invention are shown in tables 1 and 2 below.

TABLE 1

TABLE 2

Another embodiment of the invention is an amperometric detection analyte sensor comprising: a base layer; a conductive layer disposed on the base layer and comprising a working electrode; an analyte sensing layer disposed on the conductive layer; and an analyte modulation layer disposed on the analyte sensing layer. In this embodiment, the analyte modulating layer is formed from a reaction mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst. In this embodiment, the catalyst is present in the reaction mixture in an amount less than 0.2% of the reaction mixture components such that the analyte modulating layer exhibits greater thermal stability than a comparable analyte modulating layer formed from the reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture. Optionally, the reaction mixture further comprises additional components, such as a polycarbonate diol.

In typical embodiments, the analyte sensor is a glucose sensor that can be implanted in vivo. Optionally, the analyte sensor further comprises at least one of: a protein layer disposed on the analyte sensing layer; or a cover layer disposed on the analyte sensor apparatus and comprising apertures positioned on the cover layer to facilitate analyte present in an in vivo environment from contacting and diffusing through an analyte modulation layer; and contacts the analyte sensing layer. In some of these analyte sensors, the conductive layer comprises a plurality of electrodes including a working electrode, a counter electrode, and a reference electrode, such as one embodiment wherein the conductive layer comprises a plurality of working and/or counter and/or reference electrodes; and optionally, the plurality of working, counter and reference electrodes are grouped together as a unit and positionally distributed on the conductive layer in a unit repeating pattern.

In one method of making an analyte sensor for implantation into a mammal, the diisocyanate comprises hexamethylene diisocyanate and/or methylene diphenyl diisocyanate, the JEFFAMINE comprises about 45% JEFFAMINE 600 and/or JEFFAMINE 900, the polydimethylsiloxane comprises about 22.5% polydimethylsiloxane-a 15, and the polycarbonate diol comprises about 7.5% poly (1, 6-hexyl carbonate) diol. Typically, in this example, the catalyst (e.g., dibutyltin bis (ethyl 2-hexanoate)) is present in the reaction mixture in an amount less than 0.19%, 0.17%, 0.15%, 0.13%, or 0.11% of the reaction mixture (e.g., about 0.1%).

Certain amperometric detection sensor designs for use with embodiments of the present invention include a plurality of layered elements including, for example, a substrate layer having electrodes, an analyte sensing layer (e.g., an analyte sensing layer comprising glucose oxidase), and an analyte modulating layer that functions in analyte diffusion control (e.g., to modulate the amount of glucose and oxygen exposed to the analyte sensing layer). One such sensor embodiment is shown in fig. 1. Layered sensor designs incorporating the polycarbonate polymeric compositions disclosed herein as analyte modulating layers exhibit a range of material properties that overcome the challenges observed in various sensors including in vivo implanted electrochemical glucose sensors. For example, sensors designed to measure analytes in aqueous environments (e.g., in vivo implanted sensors) typically require wetting of layers before and during measurement of accurate analyte readings. Because the properties of the material may affect the rate at which it hydrates, the material properties of the membrane used in an aqueous environment will ideally promote sensor wetting, for example, for the time period between introduction of the sensor into the aqueous environment and the ability of the sensor to provide an accurate signal corresponding to the concentration of analyte in that environment. Embodiments of the present invention that include polycarbonate polymeric compositions address such issues by facilitating sensor hydration.

Furthermore, in the case of electrochemical glucose sensors that utilize a chemical reaction between glucose and glucose oxidase to generate a measurable signal, the material of the analyte modulating layer should not exacerbate (and ideally should diminish) the situation referred to in the art as the "oxygen deficit problem". In particular, because glucose oxidase based sensors require oxygen (O)₂) And glucose, an excess of oxygen is necessary for the operation of glucose sensors based on glucose oxidase relative to an excess of glucose. However, since the concentration of oxygen in the subcutaneous tissue is much lower than the glucose concentration, oxygen may be the limiting reactant in the reaction between glucose, oxygen and glucose oxidase in the sensor, a condition that compromises the ability of the sensor to produce a signal that is strictly dependent on glucose concentration. In this caseBecause the material properties may affect the rate at which compounds diffuse through the material to sites of measurable chemical reaction, the material properties of the analyte modulating layer used in an electrochemical glucose sensor that utilizes the chemical reaction between glucose and glucose oxidase to generate a measurable signal should not favor the diffusion of glucose over oxygen, for example, in a manner that causes oxygen deficiency problems. Embodiments of the present invention that include the polycarbonate polymer compositions disclosed herein do not cause oxygen deficit problems, but rather act to ameliorate oxygen deficit problems.

In addition, sensor designs using the polycarbonate polymeric compositions disclosed herein as analyte modulating layers can also overcome the complexities observed with the use of sensor materials that can exhibit different diffusion profiles (e.g., rates of analyte diffusion through the sensor material) at different temperatures. In particular, to achieve optimal sensor performance, the sensor signal output over a range of temperatures should be determined only by the level of the analyte of interest (e.g., glucose), and not by any co-matrix (e.g., O)₂) Or kinetic control parameters. However, as is known in the art, the diffusion of compounds through a polymer matrix may be temperature dependent. In the case where an analyte (e.g., glucose) diffuses through a polymer to react at a site of reaction with another compound (e.g., glucose oxidase), such a temperature-dependent diffusion profile may affect the stoichiometry of the reaction from which the sensor signal is generated, thereby allowing the skilled artisan to rely on sensor signal output solely for the analyte concentration of interest over a range of temperatures. Thus, analyte modulating compositions made from materials having analyte (e.g., glucose) diffusion profiles that are stable over a range of temperatures (e.g., 22 to 40 degrees celsius) address such issues.

The invention disclosed herein provides polycarbonate polymeric compositions that can be used as membranes for biosensors, such as amperometric glucose sensors, for example. Embodiments of the invention include, for example, a sensor having a plurality of layered elements including an analyte limiting membrane comprising a polycarbonate polymeric composition. Such polymeric membrane bodies can be used to construct electrochemical sensors for in vivo use. The film embodiments of the present invention allow for a combination of desired properties, including: enhanced hydration profile and permeability to molecules such as glucose that are stable over a range of temperatures. In addition, these polymeric films exhibit good mechanical properties for use as external polymeric films. Thus, glucose sensors incorporating such polymeric membranes show a highly desirable in vivo performance profile.

Embodiments of the present invention include both materials (e.g., polycarbonate polymer compositions) and architectures designed to facilitate sensor performance. For example, in certain embodiments of the present invention, the conductive layer comprises a plurality of working and/or counter and/or reference electrodes (e.g., 3 working electrodes, one reference electrode, and one counter electrode) in order to, for example, avoid problems associated with poor sensor hydration and/or provide redundant sensing capabilities. Optionally, the plurality of working, counter and reference electrodes are configured together as a unit and positionally distributed on the conductive layer in a repeating unit pattern. In certain embodiments of the invention, the base layer is made of a flexible material that allows the sensor to twist and bend when implanted in vivo; and the electrodes are grouped into the following configurations: facilitating in vivo fluid contact with at least one of the working electrodes when the sensor device is twisted and bent upon implantation in vivo. In some embodiments, the electrodes are grouped into the following configurations: if a portion of the sensor having one or more electrodes is removed from an in vivo environment and exposed to an ex vivo environment, the sensor is allowed to continue to operate. Typically, the sensor is operatively coupled to: a sensor input capable of receiving a signal from a sensor based on a sensed analyte; and a processor coupled to the sensor input, wherein the processor is capable of characterizing one or more signals received from the sensor. In some embodiments of the invention, a pulsed voltage is used to obtain a signal from one or more electrodes of the sensor.

The sensors disclosed herein can be made from a wide variety of materials known in the art. In one illustrative embodiment of the invention, the analyte modulation layer comprises a polyurethane/polyurea polymer formed from a mixture comprising: a diisocyanate; a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine; and a siloxane having an amino, hydroxyl, or carboxylic acid functional group at a terminal end; with this polymer, the polycarbonate with the branched acrylate-containing polymer formed from the mixture comprises: butyl acrylate, propyl acrylate, ethyl acrylate, or methyl acrylate; an amino acrylate; siloxane acrylate (siloxane-acrylate); and poly (ethylene oxide) -acrylates. Optionally, additional materials may be included in these polymer blends. For example, certain embodiments of branched acrylate polymers are formed from a reaction mixture comprising a hydroxy acrylate compound (e.g., 2-hydroxyethyl methacrylate).

The term "polyurethane/polyurea polymer" as used herein refers to a polymer containing urethane linkages, urea linkages, or combinations thereof. As is known in the art, polyurethanes are polymers consisting of chains of organic units linked by urethane (urethane) chains. Polyurethane polymers are typically formed by step growth polymerization by: reacting a monomer containing at least two isocyanate functional groups with another monomer containing at least two hydroxyl (alcohol) groups in the presence of a catalyst. The polyurea polymer is derived from the reaction product of an isocyanate component and a diamine. Typically, such polymers are formed by combining diisocyanates with alcohols and/or amines. For example, combining isophorone diisocyanate with PEG 600 and aminopropylpolysiloxane under polymerization conditions provides a polyurethane/polyurea composition having both urethane (urethane) chains and urea linkages. Such polymers are known in the art and are described, for example, in the following documents: U.S. Pat. nos. 5,777,060, 5,882,494 and 6,632,015, and PCT publication No. WO 96/30431; WO 96/18115; WO 98/13685; and WO 98/17995, the contents of each of which are incorporated by reference.

The polyurethane/polyurea compositions of the invention are prepared from a biologically acceptable polymer whose hydrophobic/hydrophilic balance can be varied over a wide range to control the ratio of the diffusion coefficient of oxygen to that of glucose and to match this ratio to the design requirements of an electrochemical glucose sensor intended for in vivo use. Such compositions may be prepared by conventional methods of polymerization of the monomers and polymers described above. The resulting polymer is soluble in solvents such as acetone or ethanol and can be formed into a film from the solution by dip coating, spray coating or spin coating.

The diisocyanates that can be used in this embodiment of the invention are those typically used to prepare biocompatible polyurethanes. Such diisocyanates are described in detail in Szycher, the medical grade polyurethane development workshop (SEMINAR ON ADVANCES IN MEDICAL GRADE POLYURETHANES), taconomick Publishing company (technical Publishing), (1995) and include both aromatic and aliphatic diisocyanates. Examples of suitable aromatic diisocyanates include toluene diisocyanate, 4' -methylene diphenyl diisocyanate, 3' -dimethyl-4, 4' -biphenyl diisocyanate, naphthalene diisocyanate, and p-phenylene diisocyanate. Suitable aliphatic diisocyanates include, for example, 1, 6-Hexamethylene Diisocyanate (HDI), trimethylhexyl diisocyanate (TMDI), trans-1, 4-cyclohexane diisocyanate (CHDI), 1, 4-cyclohexanedi (methylene isocyanate) (BDI), 1, 3-cyclohexanedi (methylene isocyanate) (H₆XDI), isophorone diisocyanate (IPDI) and 4,4' -methylenebis (cyclohexyl isocyanate) (H₂MDI). In some embodiments, the diisocyanate is isophorone diisocyanate, 1, 6-hexamethylene diisocyanate, or 4,4' methylene bis (cyclohexyl isocyanate). Many of these diisocyanates are available from commercial sources such as Aldrich Chemical Company (Milwaukee, wis., USA) or can be readily prepared by standard synthetic methods using literature procedures.

The amount of diisocyanate in the reaction mixture for the polyurethane/polyurea polymer composition is typically about 50 mol% relative to the combination of the remaining reactants. More specifically, the amount of diisocyanate used in preparing the polyurethane/polyurea polymer will be sufficient to provide at least about 100% of the-NCO groups needed to react with the hydroxyl or amino groups of the remaining reactants. For example, a polymer prepared using x moles of diisocyanate would use a moles of hydrophilic polymer (diol, diamine, or combination thereof), b moles of silicone polymer with functionalized ends, and c moles of chain extender such that x ═ a + b + c, it being understood that c may be zero.

Another reactant for preparing the polyurethane/polyurea polymers described herein is a hydrophilic polymer. The hydrophilic polymer may be a hydrophilic diol, a hydrophilic diamine, or a combination thereof. The hydrophilic diol may be a poly (alkylene) glycol, a polyester-based polyol, or a polycarbonate polyol. The term "polyalkylene glycol" as used herein refers to polymers of lower alkylene glycols such as poly (ethylene) glycol, poly (propylene) glycol, and polytetramethylene ether glycol (PTMEG). The term "polyester-based polyol" refers to polymers in which the R group is a lower alkylene group such as ethylene, 1, 3-propylene, 1, 2-propylene, 1, 4-butene, 2-dimethyl-1, 3-propylene, and the like (e.g., as depicted in figure 4 of U.S. patent No. 5,777,060). Those skilled in the art will also appreciate that the diester portion of the polymer may also be different from the six carbon diacid shown. For example, while figure 4 of U.S. patent No. 5,777,060 illustrates an adipic acid component, the present invention also contemplates the use of succinates, glutarates, and the like. The term "polycarbonate polyol" refers to a polymer having hydroxyl functionality at the chain ends and carbonate functionality within the polymer chain. The alkyl portion of the polymer is typically composed of C2 to C4 aliphatic groups, or in some embodiments, longer chain aliphatic, cycloaliphatic, or aromatic groups. The term "hydrophilic diamine" refers to any of the above hydrophilic diols, wherein the terminal hydroxyl group has been substituted with a reactive amine group or wherein the terminal hydroxyl group has been derivatized to produce a chain extension with a terminal amine group. For example, a certain hydrophilic diamine is "diamino poly (oxyalkylene)", which is a poly (alkylene) glycol in which the terminal hydroxyl groups are replaced by amino groups. The term "diamino poly (oxyalkylene)" also refers to poly (alkylene) glycols having aminoalkyl ether groups at the chain ends. An example of a suitable diamino poly (alkylene oxide) is poly (propylene glycol) bis (2-aminopropyl ether). Many of the above polymers are available from aldrich chemical company. Alternatively, conventional methods known in the art may be used for the synthesis of the polymer.

The amount of hydrophilic polymer used to prepare the linear polymer composition is typically from about 10 to about 80 mole% relative to the diisocyanate used. Typically, the amount is from about 20 mole% to about 60 mole% relative to the diisocyanate. When lower amounts of hydrophilic polymer are used, it is common to include a chain extender.

The silicone-containing polyurethane/polyurea polymers useful in the present invention are generally linear, have excellent oxygen permeability, and are substantially free of glucose permeability. Typically, the silicone polymer is a polydimethylsiloxane having two reactive functional groups (i.e., a functionality of 2). The functional group may be, for example, a hydroxyl, amino or carboxylic acid group, but is typically a hydroxyl or amino group. In some embodiments, a combination of silicone polymers may be used, wherein the first moiety comprises a hydroxyl group and the second moiety comprises an amino group. Typically, the functional groups are located at the chain ends of the silicone polymer. Many suitable silicone polymers are commercially available from sources such as The Dow Chemical Company (The Dow Chemical Company) (Midland, michx., USA) and General Electric Company (General Electric Company) (silicone Division, Schenectady, n.y., USA) in stark cadidi, n.y., USA. Still other silicone polymers can be prepared by general synthetic methods known in the art (see, e.g., U.S. patent No. 5,777,060) starting from commercially available siloxanes (United Chemical Technologies, bristol.pa., USA) for use in the present invention, the silicone polymer is typically a silicone polymer having a molecular weight of from about 400 to about 10,000, more typically a silicone polymer having a molecular weight of from about 2000 to about 4000. The amount of silicone polymer is from 10 to 90 mole% relative to the diisocyanate. Typically, the amount is about 20 to 60 mole% relative to the diisocyanate.

In one set of embodiments, the reaction mixture used to make the biocompatible film will also contain a chain extender that is an aliphatic or aromatic diol, an aliphatic or aromatic diamine, an alkanolamine, or a combination thereof (e.g., as depicted in fig. 8 of U.S. patent No. 5,777,060). Examples of suitable aliphatic chain extenders include ethylene glycol, propylene glycol, 1, 4-butanediol, 1, 6-hexanediol, ethanolamine, ethylenediamine, butanediamine, 1, 4-cyclohexanedimethanol. Aromatic chain extenders include, for example, p-bis (2-hydroxyethoxy) benzene, M-bis (2-hydroxyethoxy) benzene, Ethacure 100 (a mixture of two isomers of 2, 4-diamino-3, 5-diethyltoluene), Ethacure 300 (2, 4-diamino-3, 5-di (methylthio) toluene), 3 '-dichloro-4, 4' diaminodiphenylmethane, Polacure 740M (trimethylene glycol bis (p-aminobenzoate)), and diphenylaminomethane. The incorporation of one or more of the above chain extenders typically provides additional physical strength to the resulting biocompatible membrane, but does not significantly increase the glucose permeability of the polymer. Typically, when a relatively low amount (i.e., 10-40 mol%) of hydrophilic polymer is used, a chain extender is used. Specifically in some compositions, the chain extender is diethylene glycol present at about 40 to 60 mole% relative to the diisocyanate.

The polymerization of the above reactants may be carried out in batch form or in a solvent system. The use of a catalyst is partially required, but not essential. Suitable catalysts include dibutyltin bis (ethyl-2-hexanoate) (CAS number: 2781-10-4), dibutyltin diacetate, triethylamine, and combinations thereof. Typically, dibutyltin bis (ethyl-2-hexanoate) was used as the catalyst. Typical amounts of this catalyst used in the formulation are 0.05% to 0.2% (w/w ratio). Bulk polymerization is typically performed at an initial temperature of about 25 ℃ (ambient temperature) to about 50 ℃ to ensure adequate mixing of the reactants. Upon mixing of the reactants, an exotherm is typically observed in which the temperature rises to about 90-120 ℃. After the initial exotherm, the reaction flask can be heated at 75 ℃ to 125 ℃, with 90 ℃ to 100 ℃ being an exemplary temperature range. Heating is typically performed for one to two hours. Solution polymerization can be performed in a similar manner. Solvents suitable for solution polymerization include dimethylformamide, dimethyl sulfoxide, dimethylacetamide, halogenated solvents such as 1,2, 3-trichloropropane and ketones such as 4-methyl-2-pentanone. Typically, THF is used as the solvent. When the polymerization is performed in a solvent, heating of the reaction mixture is typically performed for three to four hours.

The polymer prepared by bulk polymerization is usually dissolved in dimethylformamide and precipitated from water. The polymer prepared in the water immiscible solvent can be isolated by vacuum stripping of the solvent. These polymers were then dissolved in dimethylformamide and precipitated from water. After thorough washing with water, the polymer can be dried under vacuum at about 50 ℃ to constant weight.

The preparation of the film can be accomplished by dissolving the dried polymer in a suitable solvent and casting the film onto a glass plate. The selection of a suitable solvent for casting generally depends on the particular polymer and the volatility of the solvent. Typically, the solvent is THF, CHCl₃、CH₂Cl₂DMF, IPA, or combinations thereof. More typically, the solvent is THF or DMF/CH₂Cl₂(2/98 vol%). The solvent was removed from the film, the resulting film was completely hydrated, its thickness was measured and the water absorption (water pickup) was determined. The films useful in the present invention typically have a water absorption of from about 20 to about 100 weight percent, typically from 30 to about 90 weight percent, and more typically from 40 to about 80 weight percent.

Oxygen diffusion coefficient and glucose diffusion coefficient can also be determined for the polymer composition alone and the polycarbonate polymeric film of the present invention. Methods for determining diffusion coefficient for the artThe skilled person is known and examples are provided in the following. Certain embodiments of the biocompatible films described herein typically have about 0.1x 10^-6cm²Sec to about 2.0x 10^-6cm²Oxygen diffusion coefficient of/sec (D)_{Oxygen gas}) And about 1x 10^-9cm²Sec to about 500x 10^-9cm²Glucose diffusion coefficient of/sec (D)_Glucose). More typically, the glucose diffusion coefficient is about 10x 10^-9cm²Sec to about 200x 10^-9cm²/sec。

Typical combinations of sensor elements

Embodiments of the present invention further comprise sensors comprising the polycarbonate polymeric compositions disclosed herein in combination with other sensor elements, such as an interference rejection membrane (e.g., an interference rejection membrane as disclosed in U.S. patent application serial No. 12/572,087, the contents of which are incorporated by reference). One such embodiment of the invention is an interference rejection membrane comprising a methacrylic polymer having a molecular weight between 100 kilodaltons and 1000 kilodaltons, wherein the methacrylic polymer is crosslinked by a hydrophilic crosslinking agent such as an organofunctional dialkoxy silane (dipodal alkoxy silane). Another embodiment of the invention is an interference rejection membrane having a primary amine polymer with a molecular weight between 4,000 daltons and 500 kilodaltons, wherein the primary amine polymer is crosslinked by a hydrophilic crosslinking agent such as glutaraldehyde. Typically, these interference rejection membranes are coated with the hydrogen peroxide conversion composition. In an illustrative embodiment, the hydrogen peroxide conversion composition includes an electrode; and the cross-linked interference rejection film is coated on the electrodes in a 0.1 μm and 1.0 μm thick layer.

In some embodiments of the invention, elements of the sensor device, such as electrodes or holes, are designed to have a particular configuration and/or to be made of a particular material and/or positioned relative to other elements in order to facilitate the function of the sensor. In one such embodiment of the invention, the working, counter and reference electrodes are distributed positionally on the base layer and/or conductive layer in the following configuration: this phenomenon may inhibit hydration and capacitive activation of the sensor circuit when the sensor device is placed in contact with a fluid including an analyte (e.g., by shielding of the suppression electrode, which may inhibit hydration and capacitive activation of the sensor circuit) facilitates sensor activation and/or maintains hydration of the working, counter and/or reference electrodes. Generally, such embodiments of the present invention facilitate sensor startup and/or initialization.

Optionally, embodiments of the device include multiple working and/or counter and/or reference electrodes (e.g., 3 working electrodes, one reference electrode, and one counter electrode), for example, to provide redundant sensing capabilities. Certain embodiments of the present invention include a single sensor. Other embodiments of the invention include multiple sensors. In some embodiments of the invention, a pulsed voltage is used to obtain a signal from one or more electrodes of the sensor. Optionally, the plurality of working, counter and reference electrodes are configured together as a unit and positionally distributed on the conductive layer in a repeating unit pattern. In certain embodiments of the invention, the elongate substrate layer is made of a flexible material that allows the sensor to twist and bend when implanted in vivo; and the electrodes are grouped into the following configurations: facilitating in vivo fluid contact with at least one of the working electrodes when the sensor device is twisted and bent upon implantation in vivo. In some embodiments, the electrodes are grouped into the following configurations: if a portion of the sensor having one or more electrodes is removed from an in vivo environment and exposed to an ex vivo environment, the sensor is allowed to continue to operate.

In certain embodiments of the present invention comprising a plurality of sensors, elements such as sensor electrodes are organized/disposed within a flexible circuit assembly. In such embodiments of the invention, the architecture of the sensor system may be designed such that the first sensor does not affect the signal generated by the second sensor, etc. (and vice versa); and causing the first sensor and the second sensor to sense from separate tissue envelopes (tissue enveloppes); the signals from the individual sensors do not interact. Also, in typical embodiments of the present invention, the sensors will be spaced a distance from each other so as to allow the sensors to be easily packaged together and/or adapted for implantation by a single insertion motion. One such embodiment of the present invention is an apparatus for monitoring an analyte in a patient, the apparatus comprising: a base element adapted to secure the device to a patient; a first piercing member coupled to and extending from the base element; a first electrochemical sensor operably coupled to the first piercing member and comprising a first electrochemical sensor electrode for determining at least one physiological characteristic of the patient at a first electrochemical sensor placement site; a second piercing member coupled to and extending from the base element; a second electrochemical sensor operably coupled to the second piercing member and comprising a second electrochemical sensor electrode for determining at least one physiological characteristic of the patient at a second electrochemical sensor placement site. In such embodiments of the invention, the at least one physiological characteristic monitored by the first electrochemical sensor or the second electrochemical sensor comprises a concentration of a naturally occurring analyte in the patient; the first piercing member positions the first electrochemical sensor in a first tissue compartment of a patient and the second piercing member positions the second electrochemical sensor in a second tissue compartment of the patient; and the first piercing member and the second piercing member are disposed on the substrate in a configuration selected to avoid a physiological response that may result from implanting the first electrochemical sensor changing a sensor signal generated by the second electrochemical sensor.

The various elements of the sensor device may be positioned at certain locations in the device and/or configured in a particular shape and/or constructed of a particular material to facilitate the strength and/or function of the sensor. One embodiment of the present invention includes an elongated substrate comprising a polyimide or dielectric ceramic material that promotes the strength and durability of the sensor. In certain embodiments of the invention, the structural features and/or relative positions of the working electrode and/or counter electrode and/or reference electrode are designed to affect the manufacture, use and/or function of the sensor. Optionally, the sensor is operatively coupled to a series of elements (e.g., electrodes, electrical conduits, contact pads, etc.) that comprise a flexible circuit. One embodiment of the invention includes an electrode having one or more rounded edges to inhibit delamination of a layer (e.g., an analyte sensing layer comprising glucose oxidase) disposed on the electrode.

In certain embodiments of the invention, the electrode of the apparatus comprises a platinum composition, and the apparatus further comprises a titanium composition disposed between the elongated base layer and the conductive layer. Optionally, in such embodiments, the device further comprises a gold composition disposed between the titanium composition and the conductive layer. Such embodiments of the present invention generally exhibit enhanced bonding and/or less corrosion and/or improved biocompatibility profiles between layered materials within the sensor. Related embodiments of the invention include methods for inhibiting corrosion of sensor elements and/or methods for improving the biocompatibility of sensor embodiments of the invention (e.g., sensors configured to use such materials).

In an exemplary embodiment of the invention, the sensor is operatively coupled to additional components (e.g., electronics), such as components designed to send and/or receive signals, monitors, processors, etc., and devices that may use the sensor data to modulate patient physiological functions, such as drug infusion pumps. For example, in some embodiments of the present invention, the sensor is operably coupled to: a sensor input capable of receiving a signal from a sensor based on a value of a physiological characteristic sensed in a mammal; and a processor coupled to the sensor input, wherein the processor is capable of characterizing one or more signals received from the sensor. A wide variety of sensor configurations as disclosed herein may be used in such systems. Optionally, for example, the sensor includes three working electrodes, one counter electrode, and one reference electrode. In certain embodiments, at least one working electrode is coated with an analyte sensing layer comprising glucose oxidase and at least one working electrode is not coated with an analyte sensing layer comprising glucose oxidase.

Diagrammatic view of a typical sensor configuration

Fig. 1 illustrates a cross-section of an exemplary sensor embodiment 100 of the present invention. This sensor embodiment is formed from a plurality of components, typically in the form of layers of various conductive and non-conductive components, disposed upon one another according to art-recognized methods disclosed herein and/or specific methods of the present invention. The components of the sensor are generally characterized herein as layers, as they allow for easy characterization of the sensor structure shown in fig. 1, for example. However, the skilled person will appreciate that in certain embodiments of the invention, the sensor components are combined such that the plurality of components form one or more heterogeneous layers. In this context, it will be understood by those skilled in the art that the order of the layered components may be changed in various embodiments of the present invention.

The embodiment shown in fig. 1 includes a substrate layer 102 for supporting the sensor 100. The base layer 102 may be made of a material such as a metal and/or ceramic and/or polymer substrate, which may be self-supporting or may be further supported by another material known in the art. Embodiments of the present invention include a conductive layer 104 disposed on and/or combined with a base layer 102. Typically, the conductive layer 104 includes one or more electrodes. The operation sensor 100 generally includes a plurality of electrodes, such as a working electrode, a counter electrode, and a reference electrode. Other embodiments may also include multiple working and/or counter and/or reference electrodes and/or one or more electrodes that perform multiple functions, such as an electrode that functions as both a reference and counter electrode.

As discussed in detail below, the base layer 102 and/or the conductive layer 104 may be created using any number of known techniques and materials. In some embodiments of the invention, the circuitry of the sensor is defined by etching the disposed conductive layer 104 into a desired conductive path pattern. A typical circuit for sensor 100 includes two or more adjacent conductive paths having a region at a proximal end to form a contact pad and a region at a distal end to form a sensor electrode. An electrically insulating cover layer 106, such as a polymer coating, may be disposed over portions of the sensor 100. Acceptable polymer coatings for use as the insulating protective cover layer 106 can include, but are not limited to, non-toxic biocompatible polymers such as silicone compounds, polyimides, biocompatible solder masks, epoxy acrylate copolymers, and the like. In the sensor of the present invention, one or more exposed areas or apertures 108 may be formed through the cover layer 106 to open the conductive layer 104 to the external environment and, for example, to allow an analyte, such as glucose, to permeate through the layers of the sensor and be sensed by the sensing element. The holes 108 may be formed by a variety of techniques including laser ablation, tape masking, chemical milling or etching or photolithographic development, and the like. In some embodiments of the present invention, a second photoresist may also be applied to the protective layer 106 during fabrication to define the areas of the protective layer to be removed to form one or more apertures 108. The exposed electrodes and/or contact pads may also be subjected to secondary processing (e.g., through holes 108) such as additional plating processes to prepare the surface and/or strengthen the conductive regions.

In the sensor configuration shown in fig. 1, an analyte sensing layer 110 (which is typically a sensor chemistry layer, meaning that the material in this layer undergoes a chemical reaction to produce a signal that can be sensed by the conductive layer) is disposed on one or more of the exposed electrodes of the conductive layer 104. In the sensor configuration shown in fig. 2B, an interference rejection membrane 120 is disposed on one or more of the exposed electrodes of the conductive layer 104, with the analyte sensing layer 110 then disposed on this interference rejection membrane 120. Typically, the analyte sensing layer 110 is an enzyme layer. Most typically, the analyte sensing layer 110 includes an enzyme capable of generating and/or utilizing oxygen and/or hydrogen peroxide, such as glucose oxidase. Optionally, the enzyme in the analyte sensing layer is combined with a second carrier protein, such as human serum albumin, bovine serum albumin, or the like. In an illustrative embodiment, an oxidoreductase enzyme, such as glucose oxidase, in the analyte sensing layer 110 reacts with glucose to produce hydrogen peroxide, which then modulates the current at the electrode. Since this adjustment of the current depends on the concentration of hydrogen peroxide, which is related to the concentration of glucose, the concentration of glucose can be determined by monitoring this adjustment of the current. In a specific embodiment of the invention, hydrogen peroxide is oxidized at a working electrode that is an anode (also referred to herein as an anodic working electrode), wherein the current generated is proportional to the hydrogen peroxide concentration. This modulation of the current caused by the change in hydrogen peroxide concentration may be monitored by any of a variety of sensor detector devices, such as a universal sensor amperometric biosensor detector or one of various other similar devices known in the art, such as the glucose monitoring device manufactured by Medtronic MiniMed.

In embodiments of the present invention, the analyte sensing layer 110 may be applied over portions of the conductive layer or over the entire area of the conductive layer. Typically, the analyte sensing layer 110 is disposed on a working electrode, which may be an anode or a cathode. Optionally, an analyte sensing layer 110 is also disposed on the counter electrode and/or the reference electrode. While the thickness of analyte sensing layer 110 may be up to about 1000 micrometers (μm), the analyte sensing layer is typically relatively thin compared to the thicknesses found in sensors previously described in the art, and typically has a thickness of, for example, less than 1 micrometer, 0.5 micrometer, 0.25 micrometer, or 0.1 micrometer. As discussed in detail below, some methods for producing the thin analyte sensing layer 110 include: the layer is brushed onto a substrate (e.g., the reactive surface of a platinum black electrode), as well as spin coating processes, dip and dry processes, low shear spray processes, ink jet printing processes, screen printing processes, and the like.

Typically, the analyte sensing layer 110 is coated and/or disposed adjacent to one or more additional layers. Optionally, one or more additional layers include a protein layer 116 disposed on the analyte sensing layer 110. Typically, the protein layer 116 comprises a protein, such as human serum albumin, bovine serum albumin, and the like. Typically, the protein layer 116 comprises human serum albumin. In some embodiments of the present invention, the additional layer comprises an analyte modulation layer 112 disposed over the analyte sensing layer 110 to modulate the proximity of the analyte to the analyte sensing layer 110. For example, the analyte modulating membrane layer 112 may include a glucose limiting membrane that regulates the amount of glucose that comes into contact with an enzyme present in the analyte sensing layer (e.g., glucose oxidase). Such glucose limiting membranes may be made from a variety of materials known to be suitable for such purposes, for example, silicone compounds such as polydimethylsiloxane, polyurethane, cellulose polyurea acetate, perfluorosulfonic acid (NAFION), polyester sulfonic acid (e.g., Kodak AQ), hydrogels, polymer blends disclosed herein, or any other suitable hydrophilic membrane known to those skilled in the art.

In some embodiments of the present invention, as illustrated in FIG. 1, an adhesion promoter layer 114 is disposed between layers, such as analyte modulation layer 112 and analyte sensing layer 110, to promote contact and/or adhesion thereof. In a particular embodiment of the present invention, as illustrated in fig. 1, an adhesion promoter layer 114 is disposed between the analyte modulation layer 112 and the protein layer 116 to promote contact and/or adhesion thereof. Adhesion promoter layer 114 may be made of any of a variety of materials known in the art to promote bonding between such layers. The adhesion promoter layer 114 typically includes a silane compound. In alternative embodiments, the proteins or similar molecules in the analyte sensing layer 110 may be sufficiently cross-linked or otherwise prepared to allow the analyte modulating membrane layer 112 to be placed in direct contact with the analyte sensing layer 110 in the absence of the adhesion promoter layer 114.

Embodiments of exemplary elements for fabricating the sensors disclosed herein are discussed below.

Typical analyte sensor compositions used in embodiments of the invention

The following disclosure provides examples of typical elements/compositions used in sensor embodiments of the present invention. Although these elements may be described as discrete units (e.g., layers), one skilled in the art will appreciate that the sensor may be designed to contain a combination of some or all of the material properties and/or functions of the elements/components discussed below (e.g., elements that act as both supporting substrate components and/or conductive components and/or matrices for analyte sensing components and further serve as electrodes in the sensor). Those skilled in the art will appreciate that these thin film analyte sensors may be adapted for use in a number of sensor systems, such as those described below.

Base composition

The sensors of the present invention generally comprise a substrate composition (see, e.g., element 102 in fig. 1). The term "substrate component" is used herein according to art-recognized dedication and refers to a component in a device that generally provides a supporting matrix for a plurality of components stacked on top of each other and comprising functional sensors. In one form, the base component comprises a thin film sheet of insulating (e.g. electrically insulating and/or water impermeable) material. The base composition may be made of various materials having desired qualities such as dielectric properties, water impermeability and air impermeability. Some materials include metallic and/or ceramic and/or polymeric substrates, and the like.

The substrate component may be self-supporting or may be further supported by another material known in the art. In one embodiment of the sensor configuration shown in FIG. 1, the substrate composition 102 comprises a ceramic. Alternatively, the substrate component comprises a polymeric material, such as a polyamide. In one illustrative embodiment, the ceramic substrate comprises primarily Al₂O₃(e.g., 96%) of the composition. The use of alumina as an insulating base component for use with implantable devices is disclosed in U.S. patent nos. 4,940,858, 4,678,868, and 6,472,122, which are incorporated herein by reference. The substrate composition of the present invention may further comprise other elements known in the art, such as a sealed through-hole (see, for example, WO 03/023388). Depending on the particular sensor design, the base composition may be a relatively thick composition (e.g., thicker than 50, 100, 200, 300, 400, 500, or 1000 microns). Alternatively, a non-conductive ceramic, such as alumina, in a thin composition, e.g., less than about 30 microns, may be utilized.

Conductive component

Electrochemical sensors of the invention generally comprise a conductive component comprising at least one electrode for measuring an analyte or a byproduct thereof (e.g., oxygen and/or hydrogen peroxide) to be determined disposed on a substrate component (see, e.g., element 104 in fig. 1). The term "conductive component" is used herein according to art-recognized terminology and refers to a conductive sensor element, such as an electrode, that is capable of measuring a detectable signal and conducting the signal to a detection device. An illustrative example of such a conductive component is one that can measure an increase or decrease in current in response to exposure to a stimulus, such as a change in the concentration of an analyte or a byproduct thereof, as compared to a reference electrode that does not undergo a change in the concentration of an analyte (a co-reactant (e.g., oxygen) or a reaction product of such an interaction (e.g., hydrogen peroxide) used when the analyte interacts with a composition present in the analyte sensing component 110, such as the enzyme glucose oxidase). Illustrative examples of such elements include electrodes capable of producing a variable detectable signal in the presence of a variable concentration of a molecule, such as hydrogen peroxide or oxygen. Typically, one of these electrodes in the conductive composition is a working electrode, which may be made of a non-corrosive metal or carbon. The carbon working electrode may be vitreous or graphitic and may be made of a solid or paste. The metal working electrode may be made of a platinum group metal comprising palladium or gold, or a non-corrosive metal conductive oxide, such as ruthenium dioxide. Alternatively, the electrode may comprise a silver/silver chloride electrode composition. The working electrode may be a wire or a thin conductive film applied to the substrate, for example by coating or printing. Typically, only a portion of the surface of the metal or carbon conductor is in electrolytic contact with the analyte-containing solution. This portion is referred to as the working surface of the electrode. The remaining surface of the electrode is typically isolated from the solution by an electrically insulating cover composition 106. Examples of useful materials for creating this protective covering component 106 include polymers such as polyimides, polytetrafluoroethylene, polyhexafluoropropylene, and silicones such as polysiloxanes.

In addition to the working electrode, the analyte sensors of the present invention typically comprise a reference electrode or a combined reference and counter electrode (also referred to as a quasi-reference electrode or counter/reference electrode). If the sensor does not have a counter/reference electrode, it may comprise a separate counter electrode, which may be made of the same or different material as the working electrode. Typical sensors of the invention have one or more working electrodes and one or more counter, reference and/or counter/reference electrodes. One embodiment of the sensor of the present invention has two, three, or four or more working electrodes. The working electrodes in the sensor may be integrally connected or they may be kept separate.

Generally, for in vivo use, embodiments of the present invention are implanted subcutaneously in the skin of a mammal to be in direct contact with bodily fluids of the mammal, such as blood. Alternatively, the sensor may be implanted in other areas within the mammalian body, such as in the intraperitoneal space. When multiple working electrodes are used, they may be implanted together or at different locations within the body. The counter, reference and/or counter/reference electrodes may also be implanted near one or more working electrodes or at other locations within the mammalian body. Embodiments of the invention include sensors that include electrodes composed of nanostructured materials. As used herein, a "nanostructured material" is an object that is fabricated to have at least one dimension that is less than 100 nm. Examples include, but are not limited to, single-walled nanotubes, double-walled nanotubes, multi-walled nanotubes, nanotube bundles, fullerenes, cocoons, nanowires, nanofibers, onions, and the like.

Interference suppressing component

The electrochemical sensors of the invention optionally comprise an interference suppressing component disposed between the electrode surface and the environment to be measured. In particular, certain sensor embodiments rely on the oxidation and/or reduction of hydrogen peroxide generated by an enzymatic reaction at the surface of the working electrode at a constant applied potential. Because amperometric detection based on direct oxidation of hydrogen peroxide requires a relatively high oxidation potential, sensors employing this detection scheme can experience interference from oxidizable substances present in biological fluids, such as ascorbic acid, uric acid, and acetamidophenol. In this context, the term "interference suppressing component" is used herein according to art-recognized terminology and refers to a coating or film in the sensor that functions to suppress stray signals generated by such oxidizable species that interfere with detecting signals generated by the analyte to be sensed. Certain interference-inhibiting components act by size exclusion (e.g., by excluding interfering species of a particular size). Examples of interference suppressing components include one or more layers or coatings of compounds such as hydrophilic cross-linked pHEMA and lysine polymers and cellulose acetate (including cellulose acetate incorporating agents such as poly (ethylene glycol), polyethersulfone, polytetrafluoroethylene, perfluorinated ionomer NAFION, polyphenylenediamine, epoxy resins, and the like). Illustrative discussions of such interference-inhibiting components are found, for example, in Ward et al, Biosensors and Bioelectronics (Biosensors and Bioelectronics) 17(2002)181-189 and Choi et al, Analytical chemistry reports (Analytical chip Acta) 461(2002)251-260, which are incorporated herein by reference. Other interference inhibiting components include, for example, interference inhibiting components where compound movement is observed to be limited based on molecular weight ranges, such as cellulose acetate as disclosed, for example, in U.S. Pat. No. 5,755,939, the contents of which are incorporated by reference. The compositions and methods of making and using them that can make additional compositions ideal for use as interference rejection membranes in certain amperometric glucose sensors having a range of undesirable material properties are disclosed herein, for example, in U.S. patent application serial No. 12/572,087.

Analyte sensing element

The electrochemical sensors of the present invention comprise an analyte sensing element (see, e.g., element 110 in fig. 1) disposed on an electrode of the sensor. The term "analyte sensing constituent" is used herein according to art-recognized terminology and refers to a constituent that includes a material that is capable of recognizing or reacting with an analyte whose presence is to be detected by the analyte sensor apparatus. Typically, this material in the analyte sensing constituent produces a detectable signal upon interaction with the analyte to be sensed, typically via electrodes of the conductive constituent. In this regard, the electrodes of the analyte sensing component and the conductive component operate in combination to produce an electrical signal that is read by a device associated with the analyte sensor. Typically, the analyte sensing component comprises an oxidoreductase enzyme (e.g. glucose oxidase) capable of reacting with and/or producing a change in concentration of a molecule, which can be measured by measuring a change in current at an electrode of a conductive component (e.g. oxygen and/or hydrogen peroxide). Enzymes capable of producing molecules such as hydrogen peroxide can be placed on the electrodes according to a number of methods known in the art. The analyte sensing constituent may coat all or a portion of the individual electrodes of the sensor. In this context, the analyte sensing constituent may coat the electrode to an equivalent extent. Alternatively, the analyte sensing constituent may coat different electrodes to different extents, with, for example, the coated surface of the working electrode being larger than the coated surface of the counter and/or reference electrode.

Typical sensor embodiments of this element of the invention utilize an enzyme (e.g. glucose oxidase) that has been combined with a second protein (e.g. albumin) in a fixed ratio and then applied to the surface of an electrode to form a thin enzyme component (e.g. an enzyme that is typically optimized for glucose oxidase stability properties). In typical embodiments, the analyte sensing constituent comprises a mixture of GOx and HSA. In a typical embodiment of an analyte sensing element having GOx, the GOx reacts with glucose present in the sensing environment (e.g., the body of a mammal) and produces hydrogen peroxide according to the reaction shown in FIG. 1, wherein the hydrogen peroxide so produced is detected at the anode at the working electrode in the conductive element.

As described above, the enzyme and the second protein (e.g., albumin) are typically treated to form a cross-linked matrix (e.g., by adding a cross-linking agent to the protein mixture). As is known in the art, the crosslinking conditions can be manipulated to modulate factors such as the retained biological activity of the enzyme, its mechanical and/or operational stability. Illustrative crosslinking procedures are described in U.S. patent application serial No. 10/335,506 and PCT publication WO 03/035891, which are incorporated herein by reference. For example, an amine crosslinking agent (such as, but not limited to, glutaraldehyde) can be added to the protein mixture.

Protein component

The electrochemical sensors of the present invention optionally comprise a protein component (see, e.g., element 116 in fig. 1) disposed between the analyte sensing component and the analyte modulating component. The term "protein component" is used herein according to art-recognized terminology and refers to a component containing a carrier protein or the like, which component is selected to be compatible with the analyte sensing component and/or the analyte modulating component. In typical embodiments, the protein component comprises albumin, such as human serum albumin. HSA concentrations may vary between about 0.5% to 30% (w/v). Typically, the HSA concentration is about 1-10% w/v, and most typically about 5% w/v. In alternative embodiments of the invention, collagen or BSA or other structural proteins used in these contexts may be used in place of or in addition to HSA. This component is typically cross-linked on the analyte sensing component according to art-recognized protocols.

Adhesion promoting ingredients

Electrochemical sensors of the invention can comprise one or more adhesion-promoting (AP) components (see, e.g., element 114 in fig. 1). The term "adhesion-promoting constituent" is used herein according to art-recognized terminology and refers to a constituent comprising a material selected to promote adhesion between adjoining constituents in a sensor. The adhesion-promoting constituent is typically disposed between the analyte sensing constituent and the analyte modulating constituent. The adhesion-promoting component is typically disposed between the optional protein component and the analyte modulating component. The adhesion promoter component may be made from any of a variety of materials known in the art for promoting bonding between such components, and may be applied by any of a variety of methods known in the art. The adhesion promoter component typically includes a silane compound, such as gamma-aminopropyltrimethoxysilane.

Using silane coupling agents, in particular of the formula R' Si (OR)₃Wherein R' is typically an aliphatic group with a terminal amine and R is a lower alkyl group to promote adhesion is known in the art (see, e.g., U.S. patent No. 5,212,050, which is incorporated herein by reference). For example, wherein silanes such as gamma-aminopropyltriethoxysilane and glutaraldehyde are used in a stepwise process to solubilize Bovine Serum Albumin (BSA) and Glucose Oxidase (GO)_X) Adhered to and co-crosslinked with the electrode surfaceChemically modified electrodes of (a) are known in the art (see, e.g., Yao, T., journal of analytical chemistry 1983,148, 27-33).

In certain embodiments of the invention, the adhesion-promoting constituent further comprises one or more compounds that may also be present in an adjacent constituent, such as a Polydimethylsiloxane (PDMS) compound, for limiting diffusion of an analyte, such as glucose, through the analyte modulating constituent. In an illustrative embodiment, the formulation comprises 0.5-20% PDMS, typically 5-15% PDMS, and most typically 10% PDMS. In certain embodiments of the invention, the adhesion-promoting component is crosslinked within the layered sensor system, and correspondingly comprises an agent selected for its ability to crosslink portions present in the proximal component, such as the analyte modulating component. In illustrative embodiments of the invention, the adhesion-promoting constituent comprises a reagent selected for its ability to crosslink amine or carboxyl moieties of proteins present in proximal constituents such as analyte sensing constituents and/or protein constituents and/or to crosslink siloxane moieties present in compounds disposed in proximal layers such as analyte modulating layers.

Analyte modulating composition

The electrochemical sensors of the present invention comprise an analyte modulating constituent (see, e.g., element 112 in fig. 1) disposed on the sensor. The term "analyte modulating component" is used herein according to art-recognized terminology and refers to a component that generally forms a membrane on the sensor that operates to modulate diffusion of one or more analytes (e.g., glucose) therethrough. In certain embodiments of the invention, the analyte modulating constituent is an analyte limiting membrane (e.g., a glucose limiting membrane) that operates to prevent or limit diffusion of one or more analytes (e.g., glucose) through the constituent. In other embodiments of the invention, the analyte modulating composition operates to facilitate diffusion of one or more analytes through the composition. Optionally, such analyte modulating components may be formed to prevent or limit the diffusion of one type of molecule (e.g., glucose) through the component, while allowing or even facilitating other typesMolecule (e.g. O)₂) Diffusing through the composition. Typically, the analyte modulating component comprises a polycarbonate polymer composition as disclosed herein.

With regard to glucose sensors, in known enzyme electrodes, glucose and oxygen from the blood and some interferents (such as ascorbic acid and uric acid) diffuse through the primary membrane of the sensor. When glucose, oxygen and interferents reach the analyte sensing constituent, an enzyme (e.g., glucose oxidase) catalyzes the conversion of glucose to hydrogen peroxide and gluconolactone. The hydrogen peroxide may diffuse back through the analyte modulating component, or it may diffuse to an electrode where it may react to form oxygen and protons to produce an electrical current proportional to the glucose concentration. The sensor membrane assembly has a variety of functions, including selectively allowing glucose to pass therethrough. In this case, an illustrative analyte modulating constituent is a semi-permeable membrane that allows water, oxygen, and at least one selective analyte to pass through and has the ability to absorb water, the membrane having a hydrophilic polymer that is soluble in water.

Various illustrative analyte modulating compositions are known in the art and are described, for example, in U.S. patent nos. 6,319,540, 5,882,494, 5,786,439, 5,777,060, 5,771,868 and 5,391,250, the disclosures of each of which are incorporated herein by reference. The hydrogels described therein are particularly suitable for use with a variety of implantable devices for which it is advantageous to provide a surrounding water component. In typical embodiments of the present invention, the analyte modulating composition comprises a polycarbonate polymeric composition disclosed herein.

Covering composition

The electrochemical sensor of the present invention comprises one or more covering elements (see, e.g., element 106 in fig. 1), typically an electrically insulating protective element. Typically, such cover components may be in the form of a coating, sheath or tube and disposed over at least a portion of the analyte modulating component. Acceptable polymeric coatings for use as insulating protective covering elements may include, but are not limited to, non-toxic biocompatible polymers such as silicone compounds, polyimides, biocompatible solder masks, epoxy acrylate copolymers, and the like. Further, these coatings may be photoimageable to facilitate photolithographic formation of holes through the conductive component. A typical covering composition comprises a spun on silicone. This ingredient may be a commercially available RTV (room temperature vulcanizing) silicone composition as known in the art. In this context, a typical chemical is polydimethylsiloxane (acetoxy based).

Illustrative embodiments of analyte sensor apparatus and associated features

The analyte sensor apparatus disclosed herein has many embodiments. A general embodiment of the present invention is an analyte sensor apparatus for implantation within a mammal. While analyte sensors are generally designed to be implantable within a mammal, the sensors are not limited to any particular environment, but can be used in a variety of contexts, for example, for analyzing most liquid samples, including biological fluids such as whole blood, lymph, plasma, serum, saliva, urine, stool, sweat, mucus, tears, cerebrospinal fluid, nasal secretions, cervical or vaginal secretions, semen, pleural fluid, amniotic fluid, peritoneal fluid, middle ear effusions, joint fluid, gastric fluid, and the like. Alternatively, a solid or dry sample may be dissolved in a suitable solvent to provide a liquid mixture suitable for analysis.

As described above, the sensor embodiments disclosed herein can be used to sense an analyte of interest in one or more physiological environments. For example, in certain embodiments, the sensor may be in direct contact with interstitial fluid, as typically occurs with subcutaneous sensors. The sensor of the present invention may also be part of a skin surface system in which interstitial glucose is extracted through the skin and brought into contact with the sensor (see, e.g., U.S. Pat. nos. 6,155,992 and 6,706,159, which are incorporated herein by reference). In other embodiments, the sensor may be in contact with blood, as commonly occurs with, for example, intravenous sensors. Sensor embodiments of the present invention further include sensors suitable for use in a variety of situations. For example, in some embodiments, the sensor may be designed for use in mobile situations, as employed by ambulatory users. Alternatively, the sensor may be designed for use in a stationary situation, as is appropriate in a clinical setting. Such sensor embodiments include, for example, sensors for monitoring one or more analytes present in one or more physiological environments in an inpatient.

The sensors of the present invention may also be incorporated into a wide variety of medical systems known in the art. The sensor of the present invention may be used, for example, in a closed-loop infusion system designed to control the rate of infusion of a drug into a user's body. Such closed-loop infusion systems may include sensors and associated meters that generate inputs to a controller that, in turn, operates a delivery system (e.g., a system that calculates a dose to be delivered by a drug infusion pump). In such cases, the meter associated with the sensor may also transmit commands to the delivery system and may be used to remotely control the delivery system. Typically, the sensor is a subcutaneous sensor in contact with interstitial fluid to monitor glucose concentration in the body of the user, and the fluid infused into the body of the user by the delivery system comprises insulin. Illustrative systems are disclosed in, for example, U.S. patent nos. 6,558,351 and 6,551,276; PCT application Nos. US99/21703 and US 99/22993; and WO 2004/008956 and WO 2004/009161, all of which are incorporated herein by reference.

Certain embodiments of the present invention measure peroxide and have advantageous properties suitable for implantation in various sites in mammals, including subcutaneous and intravenous implanted regions, as well as implantation in various non-vascular regions. Peroxide sensor designs that allow implantation in non-vascular regions have advantages over certain sensor device designs that measure oxygen due to oxygen noise issues that may arise in oxygen sensors implanted in non-vascular regions. For example, in such implantable oxygen sensor device designs, oxygen noise at the reference sensor can compromise the signal-to-noise ratio, thereby interfering with the ability of the implantable oxygen sensor device to obtain stable glucose readings in such environments. Thus, the peroxide sensors of the present invention overcome the difficulties observed with such oxygen sensors in non-vascular regions.

Certain peroxide sensor embodiments of the present invention further comprise an advantageous long-term or "permanent" sensor suitable for implantation in a mammal for a period of time greater than 30 days. In particular, as known in the art (see, e.g., ISO 10993, "Biological Evaluation of Medical Devices"), Medical Devices such as the sensors described herein may be divided into three groups based on implant duration: (1) "limited" (<24 hours), (2) "extended" (24 hours-30 days), and (3) "permanent" (>30 days). In some embodiments of the invention, the design of the peroxide sensor of the invention allows for "permanent" implantation according to this classification, i.e. >30 days. In related embodiments of the invention, the highly stable design of the peroxide sensor of the invention allows the implantable sensor to continue to operate in this regard for 2 months, 3 months, 4 months, 5 months, 6 months, or 12 months or more.

Analyte sensor apparatus and arrangement of elements

As noted above, the invention disclosed herein encompasses a number of embodiments, including sensors having an array of elements comprising a polycarbonate polymeric film. Such embodiments of the invention allow the skilled person to produce various arrangements of the analyte sensor apparatus disclosed herein. As noted above, illustrative general embodiments of sensors disclosed herein include a base layer, a cover layer, and at least one layer having sensor elements, such as electrodes, disposed between the base layer and the cover layer. Typically, the exposed portions of one or more sensor elements (e.g., working electrode, counter electrode, reference electrode, etc.) are coated with a very thin layer of material with appropriate electrode chemistry. For example, an enzyme such as lactate oxidase, glucose dehydrogenase, or hexokinase can be disposed on exposed portions of the sensor element within openings or pores defined in the cover layer. Fig. 1 illustrates a cross-section of an exemplary sensor structure 100 of the present invention. In accordance with the method of the present invention for producing the sensor structure 100, the sensor is formed of multiple layers of various conductive and non-conductive components disposed on one another.

As described above, in the sensors of the present invention, each layer of the sensor (e.g., the analyte sensing layer) may have one or more bioactive materials and/or inert materials incorporated therein. The term "incorporated" as used herein is meant to describe any state or condition in which the incorporated material is held on the outer surface of the layer or within the solid phase or supporting matrix of the layer. Thus, a material that is "incorporated" may, for example, be immobilized, physically entrapped, covalently attached to one or more functional groups of the matrix layer. Furthermore, if any method, agent, additive, or molecular linker that facilitates "incorporation" of the material is not detrimental to the invention but is consistent with the objectives of the invention, then these additional steps or agents may be employed. Of course, this definition applies to any of the embodiments of the present invention in which a biologically active molecule (e.g., an enzyme such as glucose oxidase) is "incorporated". For example, certain layers of the sensors disclosed herein comprise a proteinaceous substance, such as albumin, that acts as a cross-linkable matrix. As used herein, proteinaceous matter is meant to encompass substances that are typically derived from proteins, whether the actual substance is a native protein, an inactivated protein, a denatured protein, a hydrolyzed substance, or a derivative thereof. Examples of suitable proteinaceous materials include, but are not limited to, enzymes such as glucose oxidase and lactate oxidase, albumin (e.g., human serum albumin, bovine serum albumin, etc.), casein, gamma globulin, collagen, and collagen-derived products (e.g., fish gelatin, animal gelatin, and animal glue).

An illustrative embodiment of the invention is shown in fig. 1. This embodiment includes an electrically insulating base layer 102 for supporting the sensor 100. The electrically insulating base layer 102 may be made of a material such as a ceramic substrate, which may be self-supporting or may be further supported by another material known in the art. In an alternative embodiment, electrically insulating layer 102 comprises a polyimide substrate, such as a polyimide tape, dispensed from a reel. Providing layer 102 in this form may facilitate clean, high density mass production. Further, in some production processes using such polyimide tape, the sensor 100 may be produced on both sides of the tape.

Typical embodiments of the present invention include an analyte sensing layer disposed on a substrate layer 102. In the illustrative embodiment shown in fig. 1, the analyte sensing layer includes a conductive layer 104 disposed on an insulating substrate layer 102. Typically, the conductive layer 104 includes one or more electrodes. As described below, the conductive layer 104 may be applied using many known techniques and materials, however, the circuitry of the sensor 100 is typically defined by etching the disposed conductive layer 104 into a desired pattern of conductive paths. A typical circuit for sensor 100 includes two or more adjacent conductive paths having a region at a proximal end to form a contact pad and a region at a distal end to form a sensor electrode. An electrically insulating protective cover layer 106, such as a polymer coating, may generally be disposed over portions of the conductive layer 104. Acceptable polymer coatings for use as the insulating protective layer 106 may include, but are not limited to, non-toxic biocompatible polymers such as polyimides, biocompatible solder masks, epoxy acrylate copolymers, and the like. Further, these coatings may be photoimageable to facilitate photolithography to form holes 108 through the conductive layer 104. In certain embodiments of the invention, the analyte sensing layer is disposed on a porous metal and/or ceramic and/or polymer matrix, wherein such a combination of elements serves as an electrode in the sensor.

In the sensor of the present invention, one or more exposed areas or holes 108 may be made through the protective layer 106 to the conductive layer 104 to define contact pads and electrodes of the sensor 100. In addition to photolithographic development, the holes 108 may be formed by a number of techniques, including laser ablation, chemical milling or etching, and the like. A second photoresist may also be applied to the capping layer 106 to define the area where the protective layer is to be removed to form the aperture 108. The operation sensor 100 typically includes a plurality of electrodes, such as a working electrode and a counter electrode, that are electrically insulated from each other, but are typically positioned in close proximity to each other. Other embodiments may also include a reference electrode. Still other embodiments may utilize a separate reference element that is not formed on the sensor. The exposed electrodes and/or contact pads may also be subjected to secondary processing through the holes 108, such as additional plating processes, to prepare the surface and/or to strengthen the conductive regions.

Analyte sensing layer 110 is typically disposed on one or more of the exposed electrodes of conductive layer 104 through apertures 108. The analyte sensing layer 110 is typically a sensor chemistry layer, and most typically an enzyme layer. The analyte sensing layer 110 typically includes glucose oxidase or lactate oxidase. In such embodiments, the analyte sensing layer 110 reacts with glucose to produce hydrogen peroxide that modulates the current to the electrodes, which can be monitored to measure the amount of glucose present. The sensor chemistry layer 110 can be applied over portions of the conductive layer or over the entire area of the conductive layer. The sensor chemistry layer 110 is typically disposed on portions of the working and counter electrodes that include conductive layers. Some methods for creating the thin sensor chemistry layer 110 include spin coating processes, dip and dry processes, low shear spray processes, inkjet printing processes, screen processes, and the like. Most commonly, the thin sensor chemistry layer 110 is applied using a spin-on process.

Analyte sensing layer 110 is typically coated with one or more coatings. In some embodiments of the invention, one such coating comprises a membrane that can modulate the amount of analyte that can contact the enzyme of the analyte sensing layer. For example, the coating may include an analyte modulating membrane layer, such as a glucose limiting membrane, that regulates the amount of glucose that contacts the glucose oxidase layer on the electrode. Such glucose limiting membranes may be made from a wide variety of materials known to be suitable for such purposes, such as silicone, polyurethane, polyurea cellulose acetate, perfluorosulfonic acid, polyester sulfonic acid (Kodak AQ), hydrogel or any other membrane known to those skilled in the art. In certain embodiments of the invention, the analyte modulating layer comprises a linear polyurethane/polyurea polymer polycarbonate having a branched acrylate hydrophilic comb copolymer having a central chain and a plurality of side chains coupled to the central chain, wherein at least one side chain comprises a silicone moiety.

In some embodiments of the invention, the coating is a glucose limiting membrane layer 112 disposed over the sensor chemistry layer 110 to regulate contact of glucose with the sensor chemistry layer 110. In some embodiments of the invention, as shown in fig. 1, an adhesion promoter layer 114 is disposed between the membrane layer 112 and the sensor chemistry layer 110 to promote contact and/or adhesion thereof. Adhesion promoter layer 114 may be made of any of a variety of materials known in the art to promote bonding between such layers. The adhesion promoter layer 114 typically includes a silane compound. In alternative embodiments, the proteins or similar molecules in the sensor chemistry layer 110 may be sufficiently cross-linked or otherwise prepared to allow the film layer 112 to be placed in direct contact with the sensor chemistry layer 110 in the absence of the adhesion promoter layer 114.

As described above, embodiments of the present invention may include one or more functional coatings. The term "functional coating" as used herein means a layer that coats at least a portion of at least one surface of the sensor, more typically substantially all of the surface of the sensor and is capable of interacting with one or more analytes, such as compounds, cells and fragments thereof, etc., in the environment in which the sensor is disposed. Non-limiting examples of functional coatings include sensor chemistry layers (e.g., enzyme layers), analyte limiting layers, biocompatible layers; a layer that increases the slidability of the sensor; a layer that facilitates attachment to sensor cells; reducing the layer connecting to the sensor cells; and the like. Typically, the analyte modulation layer operates to prevent or limit diffusion of one or more analytes, such as glucose, through the layer. Optionally, such layers may be formed to prevent or limit the diffusion of one type of molecule (e.g., glucose) through the layer while allowing or even facilitating other types of molecules (e.g., O)₂) Diffusing through the layer. Illustrative functional coatings are hydrogels, such as those disclosed in U.S. patent nos. 5,786,439 and 5,391,250, the disclosures of which are incorporated herein by reference. The hydrogels described therein are particularly suitable for use with a variety of implantable devices for which it is advantageous to provide a surrounding layer of water.

Sensor embodiments disclosed herein may include a layer having a UV absorbing polymer. According to one aspect of the present invention, there is provided a sensor comprising at least one functional coating comprising a UV absorbing polymer. In some embodiments, the UV absorbing polymer is a polyurethane, polyurea, or polyurethane/polyurea copolymer. More typically, the selected UV absorbing polymer is formed from a reaction mixture comprising a diisocyanate, at least one diol, diamine, or mixtures thereof, and a multifunctional UV absorbing monomer.

The UV absorbing polymer is advantageously used in various sensor manufacturing methods, such as the sensor manufacturing methods described in: U.S. patent No. 5,390,671 entitled "Transcutaneous Sensor Insertion Set" to Lord et al; U.S. Pat. No. 5,165,407 to Wilson et al entitled "Implantable Glucose Sensor"; and U.S. Pat. No. 4,890,620 entitled "Two-Dimensional Diffusion Glucose Substrate Sensing Electrode" to Gough et al, which is incorporated herein by reference in its entirety. However, any sensor production method comprising the step of forming a UV-absorbing polymer layer above or below the sensor element is considered to be within the scope of the present invention. In particular, the method of the present invention is not limited to thin film fabrication methods and can work with other sensor fabrication methods that utilize UV laser cutting. Embodiments may work with thick film, planar or cylindrical sensors, etc., as well as other sensor shapes that require laser cutting.

As disclosed herein, the sensor of the present invention is particularly designed for use as a subcutaneous or transcutaneous glucose sensor to monitor blood glucose levels in diabetic patients. Typically, each sensor comprises a plurality of sensor elements, for example conductive elements, such as elongate thin film conductors, formed between a base layer of underlying insulating film and a cover layer of overlying insulating film.

If desired, a plurality of different sensor elements may be included in a single sensor. For example, both conductive and reactive sensor elements may be combined in one sensor, optionally with each sensor element disposed on a different portion of the substrate layer. One or more control elements may also be provided. In such embodiments, the sensor may define a plurality of openings or holes in its cover layer. One or more openings may also be defined in the cover layer directly over a portion of the base layer to provide for interaction of the base layer with one or more analytes in the environment in which the sensor is disposed. The base layer and the cover layer may comprise a variety of materials, typically polymers. In a more specific embodiment, the base layer and the cover layer comprise an insulating material such as polyimide. Openings are typically formed in the cover layer to expose the distal electrode and the proximal contact pad. For example, in a glucose monitoring application, the sensor may be placed percutaneously such that the distal electrode is in contact with the patient's blood or extracellular fluid, and the contact pad is disposed externally to facilitate connection to a monitoring device.

Analyte sensor apparatus configuration

In a clinical setting, electrochemical sensors can be used to determine accurate and relatively rapid measurements of, for example, glucose and/or lactate levels from blood samples. Conventional sensors are manufactured in large sizes, including many serviceable components, or in small planar sensors, which may be more convenient in many cases. The term "planar" as used herein refers to a well-known procedure for fabricating substantially planar structures comprising relatively thin layers of material, for example, using well-known thick film or thin film techniques. See, for example, U.S. patent No. 4,571,292 to Liu et al and U.S. patent No. 4,536,274 to Papadakis et al, both of which are incorporated herein by reference. As described below, embodiments of the invention disclosed herein have a wider range of geometric configurations (e.g., planar) than prior art sensors. Additionally, certain embodiments of the present invention include one or more of the sensors disclosed herein coupled to another device, such as a drug infusion pump.

FIG. 2 provides a diagrammatic view of an exemplary analyte sensor configuration of the present invention. Some sensor configurations are in a relatively flat "ribbon" type configuration that can be fabricated with an analyte sensor apparatus. This "ribbon" type configuration demonstrates the advantages of the sensors disclosed herein that result from spin coating of a sensing enzyme, such as glucose oxidase, which is a manufacturing step that produces an extremely thin enzyme coating that allows for highly flexible sensor geometries to be designed and produced. Such thin enzyme-coated sensors provide additional advantages, such as allowing for a smaller sensor area while maintaining sensor sensitivity, a highly desirable feature for implantable devices (e.g., smaller devices are easier to implant). Thus, sensor embodiments of the present invention that utilize a very thin analyte sensing layer that can be formed by processes such as spin coating can have a wider range of geometric configurations (e.g., planar) than sensors that utilize an enzyme layer formed by processes such as electrodeposition.

Some sensor configurations include multiple conductive elements, such as multiple working, counter, and reference electrodes. Advantages of such configurations include increased surface area, providing higher sensor sensitivity. For example, one sensor configuration incorporates a third operational sensor. One significant advantage of such a configuration is that the signals of the three sensors are averaged, thereby improving the accuracy of the sensors. Other advantages include the ability to measure multiple analytes. In particular, an analyte sensor configuration that includes electrodes in this arrangement (e.g., a plurality of working, counter and reference electrodes) can be incorporated into a plurality of analyte sensors. The measurement of a variety of analytes such as oxygen, hydrogen peroxide, glucose, lactate, potassium, calcium and any other physiologically relevant substance/analyte provides many advantages, for example such sensors can provide a linear response and are easy to calibrate and/or recalibrate.

An exemplary multi-sensor device includes a single device having: a first sensor that is cathodically polarized and is designed to measure changes in oxygen concentration that occur at the working electrode (cathode) due to glucose interaction with glucose oxidase; and a second sensor that is anodically polarized and is designed to measure changes in hydrogen peroxide concentration that occur at the working electrode (anode) due to glucose coming from the external environment and interacting with glucose oxidase. As is known in the art, in such designs, a first oxygen sensor typically experiences a decrease in current at the working electrode when oxygen contacts the sensor, while a second hydrogen peroxide sensor typically experiences an increase in current at the working electrode when hydrogen peroxide generated as shown in fig. 1 contacts the sensor. In addition, as is known in the art, the observation of the current changes occurring at the working electrode as compared to the reference electrode in the corresponding sensor system is correlated with changes in the concentrations of oxygen and hydrogen peroxide molecules, which may then be correlated with glucose concentrations in the external environment (e.g., the body of a mammal).

The analyte sensors of the present invention may be coupled to other medical devices, such as drug infusion pumps. In an illustrative variation of this aspect, the replaceable analyte sensor of the present invention may be coupled with other medical devices, such as a drug infusion pump, for example, through a port coupled to the medical device (e.g., a subcutaneous port with a locking electrical connection).

Illustrative methods and materials for making the analyte sensor apparatus of the invention

Many articles, U.S. patents and patent applications describe the prior art with the general methods and materials disclosed herein, and further describe various elements (and methods of making the same) that can be used in the sensor designs disclosed herein. These include, for example, U.S. Pat. nos. 6,413,393; 6,368,274 No; 5,786,439 No; U.S. Pat. No. 5,777,060; U.S. Pat. No. 5,391,250; 5,390,671 No; nos. 5,165,407, 4,890,620, 5,390,671, 5,390,691, 5,391,250, 5,482,473, 5,299,571, 5,568,806; U.S. patent application 20020090738; and PCT international publications No. WO 01/58348, No. WO 03/034902, No. WO 03/035117, No. WO 03/035891, No. WO 03/023388, No. WO 03/022128, No. WO 03/022352, No. WO 03/023708, No. WO 03/036255, No. WO 03/036310 and No. WO 03/074107, the contents of each of which are incorporated herein by reference.

Typical sensors for monitoring Glucose concentration In diabetic patients are further described In Shichiri et al, "In Vivo characterization of Needle Glucose Sensor Measurements of Subcutaneous Glucose concentration In Human Volunteers (In Vivo Characteristics of Properties of Needle Glucose sensors of Subcutaneous Glucose concentration In Subcutaneous Glucose Concentrations In Human volumes)", hormone and metabolism research (Horm. Metab. Res., suppl. 20:17-20 (1988); bruckel et al, "In Vivo Measurement of Subcutaneous Glucose concentration using an enzyme Glucose Sensor and the Vickers Method (In Vivo Measurement of Subcutaneous Glucose Concentrations with an Enzymatic Glucose Sensor and a Wick Method)," J.Clin.Wochenschr 491. (67: 495 (1989)); and Pickup et al, "in vivo molecular sensing of diabetes: implantable Glucose sensors (In Vivo Molecular Sensing In Diabetes cells: An Implantable Glucose Sensor with Direct Electron Transfer), "Diabetes (Diabetes)," 32:213- "217 (1989). Other sensors are described, for example, in Reach et al, Advance in IMPLANTABLE DEVICES (ADVANCES IN Implantable DEVICES), A.Turner (ed., London JAI Press, Chapter 1, (1993), which is incorporated herein by reference.

An exemplary embodiment of the invention disclosed herein is a method of manufacturing a sensor device for implantation in a mammal, the method comprising the steps of: providing a base layer; forming a conductive layer on the base layer, wherein the conductive layer comprises electrodes (and typically a working electrode, a reference electrode, and a counter electrode); forming an analyte sensing layer on the conductive layer, wherein the analyte sensing layer comprises a composition that can alter the current at an electrode in the conductive layer in the presence of an analyte; optionally forming a protein layer on the analyte sensing layer; forming an adhesion promoting layer on the analyte sensing layer or the optional protein layer; forming an analyte modulation layer disposed on the adhesion promoting layer, wherein the analyte modulation layer comprises a composition that modulates diffusion of an analyte therethrough; and forming a cover layer disposed over at least a portion of the analyte modulation layer, wherein the cover layer further comprises an aperture over at least a portion of the analyte modulation layer. In certain embodiments of the present invention, the analyte modulating layer comprises a linear polyurethane/polyurea polymer polycarbonate having a branched acrylate copolymer having a central chain and a plurality of side chains coupled to the central chain. In some embodiments of these methods, the analyte sensor apparatus is formed in a planar geometric configuration.

As disclosed herein, the various layers of the sensor can be fabricated to exhibit a variety of different characteristics that can be manipulated according to the particular design of the sensor. For example, the adhesion promoting layer comprises a compound, typically a silane composition, selected for its ability to stabilize the overall sensor structure. In some embodiments of the invention, the analyte sensing layer is formed by a spin coating process and has a thickness selected from the group consisting of: heights are less than 1 micron, 0.5 micron, 0.25 micron, and 0.1 micron.

The method of making a sensor generally comprises the step of forming a protein layer on the analyte sensing layer, wherein the protein within the protein layer is an albumin selected from the group consisting of: bovine serum albumin and human serum albumin. The method of making a sensor generally comprises the step of forming an analyte sensing layer comprising an enzyme composition selected from the group consisting of: glucose oxidase, glucose dehydrogenase, lactate oxidase, hexokinase, and lactate dehydrogenase. In such methods, the analyte sensing layer typically includes a carrier protein composition in a substantially fixed ratio to the enzyme, and the enzyme and carrier protein are distributed in a substantially uniform manner throughout the analyte sensing layer.

The electrodes of the present invention can be formed from a wide variety of materials known in the art. For example, the electrode may be made of a noble transition metal (noble transition metal). Metals such as gold, platinum, silver, rhodium, iridium, ruthenium, palladium, or osmium may be suitable for various embodiments of the present invention. Other compositions, such as carbon or mercury, are also useful in certain sensor embodiments. Of these metals, silver, gold, or platinum are commonly used as reference electrode metals. A subsequently chlorinated silver electrode is usually used as a reference electrode. These metals may be deposited by any means known in the art, including the plasma deposition methods cited above, or by electroless methods, which may involve depositing the metal onto a previously metallized region while the substrate is immersed in a solution containing a metal salt and a reducing agent. The electroless process continues as the reducing agent donates electrons to the conductive (metallized) surface, with concomitant reduction of the metal salt at the conductive surface. The result is an adsorbed metal layer. (for additional discussion of Electroless methods, see: Wise, E.M., Palladium, Recovery, Properties, and Uses, Academic Press, N.Y. (1988), Wong, K.et al, Plating and Surface polishing, 1988,75,70-76, Matsuoka, M.et al, 1988,75,102-106, and Pearlstein, F. "Electroless Plating (Electroplate Plating)", "Modern Plating (Modern Plating), Lowenheim, F.A., eds., York, N.Y. (19731). However, such metal deposition processes must produce structures with excellent metal-to-metal adhesion and minimal surface contamination to provide a high density of active sites to the catalytic metal electrode surface. Such high density of active sites is a property necessary for efficient redox conversion of an electrically active species such as hydrogen peroxide.

In an exemplary embodiment of the invention, a substrate layer is first coated with a thin film conductive layer by electrode deposition, surface sputtering, or other suitable process steps. In one embodiment, this conductive layer may be provided as a plurality of thin film conductive layers, such as an initial chromium-based layer suitable for chemical adhesion to a polyimide-based base layer, a gold-based thin film layer and a chromium-based thin film layer that are subsequently formed in sequence. In alternative embodiments, other electrode layer configurations or materials may be used. The conductive layer is then covered with a selected photoresist coating in accordance with conventional photolithography techniques, and a contact mask may be applied over the photoresist coating for suitable photoimaging. The contact mask typically contains one or more patterns of conductor traces for proper exposure of the photoresist coating, followed by an etching step to leave a plurality of conductive sensor traces on the base layer. In an exemplary sensor configuration designed for use as a subcutaneous glucose sensor, each sensor trace may contain three parallel sensor elements corresponding to three separate electrodes (e.g., a working electrode, a counter electrode, and a reference electrode).

Portions of the sensor conductive layer are typically covered by an insulating cover layer, which is typically a material such as a silicon polymer and/or polyimide. The insulating cover layer may be applied in any desired manner. In an exemplary procedure, the insulating cover layer is applied over the sensor traces as a liquid layer, after which the substrate is rotated to distribute the liquid material as a thin film over the sensor traces and to extend the liquid material as a thin film beyond the marginal margin of the sensor traces that are in sealing contact with the base layer. Such liquid material may then be subjected to one or more suitable radiation and/or chemical and/or thermal curing steps as known in the art. In alternative embodiments, the liquid material may be applied using spraying techniques or any other desired application. Various insulating layer materials may be used, such as photoimageable epoxy acrylate, with illustrative materials including photoimageable polyimide available from OCG corporation of western patison, nj under product number 7020.

As described above, optionally, after exposing the sensor tip through the opening, appropriate electrode chemistries defining the distal electrode may be applied to the sensor tip. In an illustrative sensor embodiment having three electrodes for use as a glucose sensor, an enzyme (typically glucose oxidase) is disposed within one of the openings, thus coating one of the sensor tips to define the working electrode. One or both of the other electrodes may be provided with the same coating as the working electrode. Alternatively, the other two electrodes may be provided with other suitable chemicals, such as other enzymes, uncoated or provided with chemicals to define the reference and counter electrodes of the electrochemical sensor.

Methods for producing the extremely thin enzymatic coatings of the present invention include spin coating processes, dip and dry processes, low shear spray processes, inkjet printing processes, screen processes, and the like. Since the skilled person can easily determine the thickness of the enzyme coating applied by the process in the art, the skilled person can easily identify methods that are capable of producing the extremely thin coatings of the present invention. Typically, such coatings are steam crosslinked after their application. Surprisingly, the material properties of the sensors produced by these processes exceed those of sensors having coatings produced by electrodeposition, including improved lifetime, linearity, regularity, and improved signal-to-noise ratio. In addition, embodiments of the present invention utilizing glucose oxidase coatings formed by such processes are designed to recycle hydrogen peroxide and improve the biocompatibility profile of such sensors.

Sensors produced by processes such as spin coating processes also avoid other problems associated with electrodeposition, such as problems associated with stress of materials placed on the sensor during the electrodeposition process. In particular, the electrodeposition process is observed to produce mechanical stresses on the sensor, for example, mechanical stresses produced by tensile and/or compressive forces. In some cases, such mechanical stresses may result in a sensor having a coating that tends to crack or delaminate to some extent. This is not observed in coatings that are placed on the sensor by spin coating or other low stress processes. Thus, yet another embodiment of the present invention is a method of avoiding electrodeposition-affected cracking and/or delamination of a coating on a sensor, the method comprising applying the coating by a spin-coating process.

Methods for using the analyte sensor apparatus of the present invention

A related embodiment of the invention is a method of sensing an analyte in a mammal, the method comprising implanting an analyte sensor embodiment disclosed herein into the mammal, and then sensing a change in current at the working electrode and correlating the change in current with the presence of the analyte such that the analyte is sensed. The analyte sensor may be anodically polarized such that the working electrode that senses the change in current is an anode or cathodically polarized such that the working electrode that senses the change in current is a cathode. In one such method, an analyte sensor apparatus senses glucose in a mammal. In alternative embodiments, the analyte sensor apparatus senses lactate, potassium, calcium, oxygen, pH, and/or any physiologically relevant analyte in the mammal.

Certain analyte sensors having the structure discussed above have many highly desirable characteristics that allow for a variety of methods for sensing analytes in mammals. For example, in such methods, an analyte sensor apparatus implanted in a mammal is used to sense an analyte in the body of the mammal for more than 1 month, more than 2 months, more than 3 months, more than 4 months, more than 5 months, or more than 6 months. Typically, an analyte sensor apparatus so implanted in a mammal senses a change in current in response to an analyte within 15 minutes, 10 minutes, 5 minutes or 2 minutes of the analyte contacting the sensor. In such methods, the sensor may be implanted in various locations within the mammalian body, such as in both vascular and non-vascular spaces.

Examples of the invention

The following examples are given to aid in the understanding of the invention, but it should be understood that the invention is not limited to the specific materials or procedures of the examples. All materials used in the examples were obtained from commercial sources.

Example 1: an illustrative polyurea/polyurethane polymer was synthesized and characterized using conventional methods:

the disclosure provided herein, in combination with what is known in the art, demonstrates that functional linear polyurethane/polyurea polymers can be made from a number of formulations, such as the following: U.S. Pat. nos. 5,777,060; nos. 5,882,494; nos. 6,642,015; and PCT publication No. WO 96/30431; WO 96/18115; WO 98/13685; and WO 98/17995, the contents of which are incorporated herein by reference. Certain of these polymers provide formulations that are useful as Glucose Limiting Membranes (GLMs).

Standard GLM formulations used to make embodiments of the invention include:

25 mol% Polymethylsiloxane (PDMS), trimethylsilyl end-capping, 25-35 centistokes;

75 mol% of polypropylene glycol diamine (Jeffamine 600, polyethylene glycol amine with molecular weight of about 600); and 50 mol% of a diisocyanate (e.g., 4,4' -diisocyanate).

Such standard GLM formulations and methods of their synthesis are disclosed, for example, in U.S. Pat. nos. 6,642,015, 5,777,060, and 6,642,015.

Another formulation used in embodiments of the present invention is referred to as "semi-permeable GLM" because it is observed that its glucose permeability is half that of the standard formulation described above. In standard GLM Jeffamine/PDMS quantitative 3/1 (molar ratio). In contrast, in "semi-permeable GLM", this ratio is changed such that Jeffamine/PDMS is 12/1. Such semi-permeable GLM can be used, for example, to reduce the wt% of GLM urea in the overall polymer blend to achieve a particular Isig (or glucose permeability). Also, the presence of more GLM-acrylate polymer in the polymer blend may enhance adhesion between the polycarbonate polymeric film layer and the proximal layer (e.g., a layer comprising glucose oxidase) in the sensor.

Claims

1. A method of increasing the thermal stability of a biocompatible film formed from a reaction mixture comprising:

a diisocyanate;

a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine;

a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and a catalyst;

the method includes forming the reaction mixture such that the catalyst is present in the reaction mixture in an amount of less than 0.2% of the reaction mixture components;

thereby increasing the thermal stability of the biocompatible membrane as compared to a comparable membrane formed from a reaction mixture in which the catalyst is present in the reaction mixture in an amount greater than or equal to 0.2% of the reaction mixture.

2. The method of claim 1, wherein the reaction mixture further comprises a polycarbonate diol.

3. The method of claim 1, wherein the catalyst is present in the reaction mixture in an amount of less than 0.11% of the reaction mixture.

4. The method of claim 1, wherein:

(a) the diisocyanate comprises hexamethylene diisocyanate and/or methylene diphenyl diisocyanate;

(b) the hydrophilic polymer comprising a hydrophilic diol or hydrophilic diamine comprises JEFFAMINE;

(c) the siloxane having an amino, hydroxyl, or carboxylic acid functional group at a terminal end includes polydimethylsiloxane.

5. The method of claim 2, wherein the polycarbonate diol comprises poly (1, 6-hexyl carbonate) diol and/or poly (1, 6-hexyl-1, 5-pentyl carbonate) diol.

6. The biocompatible composition of claim 2, wherein:

(a) the diisocyanate comprises:

17 to 23 weight percent hexamethylene diisocyanate; and

0 to 8.5 percent by weight of methylene diphenyl diisocyanate;

(b) the JEFFAMINE comprises 28-51 wt% of JEFFAMINE 600 and/or JEFFAMINE 900;

(c) the polydimethylsiloxane comprises 14 to 48 weight percent of polydimethylsiloxane-A15; and is

(d) The polycarbonate diol comprises 7.5 to 19 weight percent poly (1, 6-hexylcarbonate) diol.

7. The biocompatible composition of claim 6, wherein:

(a) the diisocyanate comprises:

about 22% hexamethylene diisocyanate; and

about 3.5% methylene diphenyl diisocyanate;

(b) JEFFAMINE comprises about 45% JEFFAMINE 600 and/or JEFFAMINE 900;

(c) the polydimethylsiloxane included approximately 22.5% polydimethylsiloxane-A15; and is

(d) The polycarbonate diol comprises about 7.5% poly (1, 6-hexyl carbonate) diol.

8. The biocompatible composition according to claim 1, wherein water is added as a chain extender in the reaction mixture of the polyurea-polyurethane copolymer.

9. The method of claim 1, wherein the thermal stability of the biocompatible membrane is measured by observing a change in the molecular weight of the biocompatible membrane during maintenance at a temperature of 60 ℃ for at least 3 days, 5 days, or 7 days.

10. An amperometric detection analyte sensor comprising:

a base layer;

a conductive layer disposed on the base layer and comprising a working electrode;

an analyte sensing layer disposed on the conductive layer; and

an analyte modulation layer disposed on the analyte sensing layer, wherein the analyte modulation layer:

(a) formed from a reaction mixture comprising:

a diisocyanate;

a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine;

a siloxane having amino, hydroxyl, or carboxylic acid functional groups at the terminal ends; and

a catalyst present in the reaction mixture in an amount of less than 0.2% of the reaction mixture components; and is

(b) Exhibits greater thermal stability compared to a comparable analyte modulating layer formed from a reaction mixture in which the catalyst is present in the formulation in an amount greater than or equal to 0.2% of the reaction mixture.

11. The analyte sensor of claim 10, which is an implantable glucose sensor.

12. The analyte sensor of claim 10, further comprising at least one of:

a protein layer disposed on the analyte sensing layer; or

A cover layer disposed on the analyte sensor apparatus, wherein the cover layer comprises pores positioned on the cover layer to facilitate analyte present in an in vivo environment from contacting and diffusing through the analyte modulation layer; and contacts the analyte sensing layer.

13. The analyte sensor of claim 10, wherein the conductive layer comprises a plurality of electrodes including a working electrode, a counter electrode, and a reference electrode.

14. The analyte sensor of claim 13, wherein the conductive layer comprises a plurality of working and/or counter and/or reference electrodes; and optionally, the plurality of working, counter and reference electrodes are grouped together as a unit and positionally distributed on the conductive layer in a unit repeating pattern.

15. A method of manufacturing an analyte sensor for implantation within a mammal, the method comprising the steps of:

providing a base layer;

forming a conductive layer on the base layer, wherein the conductive layer includes a working electrode;

forming an analyte sensing layer on the conductive layer, wherein the analyte sensing layer comprises an oxidoreductase;

forming an analyte modulation layer on the analyte sensing layer, wherein the analyte modulation layer

(a) Formed from a reaction mixture comprising:

a diisocyanate;

a hydrophilic polymer comprising a hydrophilic diol or a hydrophilic diamine;

16. The method of claim 15, wherein the reaction mixture further comprises a polycarbonate diol.

17. The method of claim 16, wherein:

(b) JEFFAMINE comprises about 45% JEFFAMINE 600 and/or JEFFAMINE 900;

18. The method of claim 17, wherein:

(a) the diisocyanate comprises:

about 22% hexamethylene diisocyanate; and

about 3.5% methylene diphenyl diisocyanate;

(b) JEFFAMINE comprises about 45% JEFFAMINE 600 and/or JEFFAMINE 900;

19. The method of claim 15, wherein water is added as a chain extender to the polyurea-polyurethane copolymer reaction mixture.

20. The method of claim 15, wherein the catalyst is present in the reaction mixture in an amount of less than 0.11% of the reaction mixture.