CA2428610A1 - Hydrophilic polymeric material for coating biosensors - Google Patents
Hydrophilic polymeric material for coating biosensors Download PDFInfo
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- CA2428610A1 CA2428610A1 CA002428610A CA2428610A CA2428610A1 CA 2428610 A1 CA2428610 A1 CA 2428610A1 CA 002428610 A CA002428610 A CA 002428610A CA 2428610 A CA2428610 A CA 2428610A CA 2428610 A1 CA2428610 A1 CA 2428610A1
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/61—Polysiloxanes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/48—Polyethers
- C08G18/50—Polyethers having heteroatoms other than oxygen
- C08G18/5021—Polyethers having heteroatoms other than oxygen having nitrogen
- C08G18/5024—Polyethers having heteroatoms other than oxygen having nitrogen containing primary and/or secondary amino groups
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/65—Low-molecular-weight compounds having active hydrogen with high-molecular-weight compounds having active hydrogen
- C08G18/66—Compounds of groups C08G18/42, C08G18/48, or C08G18/52
- C08G18/6666—Compounds of group C08G18/48 or C08G18/52
- C08G18/667—Compounds of group C08G18/48 or C08G18/52 with compounds of group C08G18/32 or polyamines of C08G18/38
- C08G18/6681—Compounds of group C08G18/48 or C08G18/52 with compounds of group C08G18/32 or polyamines of C08G18/38 with compounds of group C08G18/32 or C08G18/3271 and/or polyamines of C08G18/38
- C08G18/6685—Compounds of group C08G18/48 or C08G18/52 with compounds of group C08G18/32 or polyamines of C08G18/38 with compounds of group C08G18/32 or C08G18/3271 and/or polyamines of C08G18/38 with compounds of group C08G18/3225 or polyamines of C08G18/38
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
- C09D175/02—Polyureas
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- C—CHEMISTRY; METALLURGY
- C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
- C12Q—MEASURING OR TESTING PROCESSES INVOLVING ENZYMES, NUCLEIC ACIDS OR MICROORGANISMS; COMPOSITIONS OR TEST PAPERS THEREFOR; PROCESSES OF PREPARING SUCH COMPOSITIONS; CONDITION-RESPONSIVE CONTROL IN MICROBIOLOGICAL OR ENZYMOLOGICAL PROCESSES
- C12Q1/00—Measuring or testing processes involving enzymes, nucleic acids or microorganisms; Compositions therefor; Processes of preparing such compositions
- C12Q1/001—Enzyme electrodes
- C12Q1/002—Electrode membranes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31551—Of polyamidoester [polyurethane, polyisocyanate, polycarbamate, etc.]
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/31504—Composite [nonstructural laminate]
- Y10T428/31652—Of asbestos
- Y10T428/31663—As siloxane, silicone or silane
Abstract
Disclosed is a biocompatible membrane comprising a hydrophilic polyurea composition. The hydrophilic polyurea composition comprises the product of a reaction mixture comprising (a) an amino terminated polysiloxane, (b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000, and (c) diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture. In this mixture, (a) and (b) constitute a polymeric portion of the reaction mixture, and the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 2,000 to about 10,000. Also provided are biosensors coated with a membrane of the invention, and methods of using such biosensors to measure an analyte in a tissue of a subject.
Description
HYDROPHILIC POLYMERIC MATERIAL FOR COATING BIOSENSORS
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to polymeric materials and to methods of making and using such materials. The polymeric materials are hydrophilic, biocompatible, and suitable for use with biosensors, such as glucose sensors.
BACKGROUND OF THE INVENTION
Biosensors are small devices that use biological recognition properties for selective detection of various analytes or biomolecules. Typically, the sensor will produce a signal that is quantitatively related to the concentration of the analyte. To achieve a quantitative signal, a recognition molecule or combination of molecules is often immobilized at a suitable transducer, which converts the biological recognition event into a quantitative response.
The need for the continuous monitoring of biological markers (analytes) in medicine has sparked a tremendous interest in the study of biosensors in recent years.
Without question, the greatest interest has been geared toward the development of sensors to detect glucose. In particular, enzymatic (amperometzic) glucose electrodes have been studied in more detail than any other biosensors. Electroenzymatic biosensors use enzymes to convert a concentration of analyte to an electrical signal.
Immunological biosensors rely on molecular recognition of an analyte by, for example, antibodies. Chemoreceptor biosensors use chemoreceptor arrays such as those of the olfactory system or nerve fibers from the antennules of the blue crab Callinectes sapidus to detect the presence of amino acids in concentrations as low as 10v M. For a review of some of the operating principles of biosensors, see Bergveld, et al., Advances in Biosensors, Supplement 1, p. 31-91, Turner ed., and Collison, et al., Anal.
Chem. 62:425-437 (1990).
Regardless of the type of biosensor, each will possess certain properties to function in viva and provide an adequate signal. First, the elements of the biosensor should be compatible with the tissue to which it is attached, and be adequately safe such that allergic or toxic effects are not exerted. Further, the sensor should be shielded from the environment to control drift in the generated signal. Finally, the sensor should accurately measure the analyte in the presence of proteins, electrolytes and medications, which may have the potential to interfere.
The biosensor of interest is an amperometric glucose sensor. There are several reasons for the wide-ranging interest in glucose sensors. In the healthcare arena, enzymatic glucose test strips are useful for monitoring the blood sugar of patients with diabetes mellitus. A sensor that has the ability to continuously monitor the blood, or interstitial glucose of a person with diabetes could provide great insight into the level of control that they have over their disease and avoid the need fox repeated blood draws.
Additionally, a continuously monitoring glucose sensor is one of the critical components necessary for the development of an artificial pancreas. To make such a system possible, a reliable glucose sensor must communicate with an insulin pump.
An additional commercial application of this technology focuses on sensors that can be used to monitor fermentation reactions in the biotechnology industry.
From a scientific and commercial standpoint, interest has grown beyond glucose to other analytes for the diagnosis of numerous medical conditions other than diabetes.
Amperometric glucose sensors and oxido-reductase enzymes that use 02 as a co-substrate, and are designed for subcutaneous or intravenous use, typically require both an outer membrane and an anti-interference membrane. The necessity for two distinct membranes is largely due to the fundamental nature of the sensor, as well as the environment in which the measurement is made.
A glucose sensor works by a reaction in which glucose reacts with oxygen in the presence of glucose oxidase (GOd) to form gluconolactone and hydrogen peroxide. The gluconolactone further reacts with water to hydrolyze the lactone ring and produce gluconic acid. The H20z formed is electrochemically oxidized at an electrode as shown below (Equation 1):
HzOz -~ Oz +2e- +2H+ (I) The current measured by the sensor/potentiostat (+0.5 to +0.7 v oxidation at Pt black electrode) is the result of the two electrons generated by the oxidation of the HzOz.
Alternatively, one can measure the decrease in the oxygen by amperometric measurement (-0.5 to -1 V reduction at a Pt black electrode).
The stoichiometty of the GOd reaction points to a challenge of developing a reliable glucose sensor. If oxygen and glucose are present in equimolar concentrations, then the HZOz is stoichiometrically related to the amount of glucose that reacts at the enzyme. In this case, the ultimate current is also proportional to the amount of glucose that reacts with the enzyme. If there is insufficient oxygen for all of the glucose to react with the enzyme, then the current will be proportional to the oxygen concentration, not the glucose concentration. For the sensor to be a true glucose sensor, glucose must be the limiting reagent, i.e. the Oz concentration must be in excess for all potential glucose concentrations. For example, the glucose concentration in the body of a diabetic patient can vary from 2 to 30 mM (millimoles per liter or 36 to 540 mg/dl), whereas the typical oxygen concentration in the tissue is 0.02 to 0.2 mM (see, Fisher, et al., Biomed.
Biochem. Acta. 48:965-971 (1989). This ratio in the body means that the sensor would be running in the Michaelis Menten limited regime and would be very insensitive to small changes in the glucose concentration. This problem has been called the "oxygen deficit problem". Accordingly, a method ox system must be devised to either increase the Oz in the GOd enzyme layer, decrease the glucose concentration, or devise a sensor that does not use Oz.
There is a need fox a glucose sensor having a biocompatible membrane with an improved ratio of its oxygen permeability to it glucose permeability, and that offers physical and biological stability and strength, adhesion to the substrate, processibility (i.e.
solubility in common organic solvents for the development of coatings from polymer lacquer and the ability to cut using laser ablation or other large scale processing method), the ability to be synthesized and manufactured in reasonable quantities and at reasonable prices, , and compatibility with the enzyme as deposited on the sensor. The present invention fulfills these needs and provides other related advantages.
SUMMARY OF THE INVENTION
The invention provides a biocompatible membrane comprising a hydrophilic polyurea composition. The hydrophilic polyuxea composition comprises the product of a reaction mixture comprising (a) an amino terminated polysiloxane, (b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of 1o polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000, and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture. In this mixture, 15 (a) and (b) constitute a polymeric portion of the reaction mixture, and when the mixture is reacted with (c), the end product polymer has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 2,000 to about 10,000. In a preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 3,000 to 20 about 7,000. In a more preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 5,000 to about 7,000.
The biocompatible membrane of the invention can include a hydrophilic polymer that comprises a poly(pxopylene glycol)-block-polyethylene glycol) bis(2-aminopxopyl 25 ether). The polysiloxane preferably has a molecular weight of about 500 to about 3,500, and most preferably, about 2,500. In some embodiments, the reaction mixture further comprises a chain extender, such as N-methyl diethanolamine, ethylene diamine, butane diol, diethylene glycol, propane diol or water. The biocompatible membrane of the invention can be the product of a mixture having a glucose diffusion coefficient of from about 1 x 10-'~ cm2/s to about 200 x 10 '' cm2/s at 37°C, or preferably, from about 2.5 x 10v cm2/s to about 10 x 10v cmz/s at 37°C.
In a preferred embodiment, the polysiloxane content is from about 15 mole percent to about 75 mole percent of the polymeric portion of the mixture, or more preferably, about 50 mole percent of the polymeric portion of the mixture. In one embodiment, the hydrophilic polymer comprises a combination of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 600 and a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 900. In another embodiment, the polymeric portion of the mixture comprises about 50 mole percent polysiloxane, about 25 mole percent hydrophilic polymer having an average molecular weight of about 600, and about 25 mole percent hydrophilic polymer having an average molecular weight of about 900. Preferably, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol. A
preferred diamino terminated copolymer of polypropylene glycol and polyethylene glycol is polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether).
The invention further provides an implantable biosensor for measuring an analyte in biological tissue, the biosensor having a coating comprising a biocompatible membrane of the invention. The implantable biosensor can further comprise a transducer that generates a signal upon contact with the analyte. In a preferred embodiment, the analyte is glucose and the transducer is glucose oxidase.
The invention additionally provides a method of measuring an analyte in a tissue of a subject. The method comprises introducing an implantable biosensor of the invention into the tissue of the subject, and detecting the signal generated by the transducer. The amount of signal corresponds to the amount of analyte.
Preferably, the analyte is glucose and the transducer is glucose oxidase.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a schematic illustration of polymer formation using water as a chain extender and starting with a polyol diamine, a polysiloxane diamine and hexamethylene diisocyanate.
DETAILED DESCRIPTION
All scientific and technical terms used in this application have meanings commonly used in the art unless otherwise specified. As used in this application, the following words or phrases have the meanings specified.
As used herein, the term "polyurea" refers to a polymer containing urea linkages.
Such polymers may additionally contain urethane linkages. Typically, such polymers are formed by combining diisocyanates with amines and/or alcohols. For example, combining isophorone diisocyanate with PEG 600 and aminopropyl polysiloxane under polymerizing conditions provides a polyurethane/polyurea composition having both urethane (carbamate) linkages and urea linkages.
As used herein, "adhered to" or "adhered thereto" means stuck to or fused with such that a substance adhered to a surface remains substantially attached to or closely associated with the surface.
As used herein, "a" or "an" means at least one, and unless clearly indicated otherwise, includes a plurality.
Overview The invention provides hydrophilic glucose limiting polymeric materials that offer improved hydration and faster response times. The superior hydration characteristics of the polymeric materials provide improved biocompatibility and resistance to biofouling. The increased hydrophilicity of the material provides a polymer that can be coated onto a biosensor without requiring a second coating to enhance surface wetting of the device. In addition, the invention offers polymeric materials whose overall polymeric structure can be controlled by use of a diamine or diol chain extender instead of water. The invention additionally provides polymer blends that offer advantageous features over individual polymeric materials that can be selected in accordance with desired characteristics. Also provided are biosensors having a biocompatible membrane of the invention adhered thereto, and methods of measuring an analyte in a tissue of a subject using such a biosensor.
Three characteristics of the biocompatible membranes of the invention that are of particular interest axe glucose permeability, oxygen permeability, and the thermal dependence of these permeabilities. A preferred membrane has a permeability constant for glucose mass transport through the material that approximates 5.0 x 10-cmz/s at 37°C. Additionally, a ratio of oxygen permeability to glucose permeability of greater than about 3000 is preferred. Generally, the higher the permeability ratio, the better, with the exception of a ratio of infinity, which would result from a glucose permeability approaching zero. Also preferred is a membrane that exhibits minimal change in oxygen and glucose permeability in response to temperature changes.
Biocom~atible Membranes A glucose sensor intended for in vivo use requires that the supply of oxygen in the vicinity of the sensing element not be depleted. Additionally, the glucose should diffuse to the sensor at a controlled rate. Overall, the membrane should control the relative rates of diffusion of oxygen and glucose to the sensor so that the local concentration of oxygen is not depleted. Additionally, glucose sensors intended for in vivo use must also be biocompatible with the body, and they must be able to function in an environment in which harsh inflammatory components brought on by the process of tissue injury and healing are present. Furthermore, these membranes must resist against the adhesion of biological components (biofouling) such as cells and proteins that can interfere with a sensor's performance. Thus, the enzymes) used in such sensors must be protected from degradation or denaturation, while the elements of such sensors must be protected from molecules that would foul the sensors or their accuracy will decrease over time.
In one aspect, the present invention provides a biocompatible membrane comprising a hydrophilic polyurea composition. The hydrophilic polyurea composition comprises the product of a reaction mixture comprising (a) an amino terminated polysiloxane, (b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000, and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture. In this mixture, (a) and (b) constitute a polymeric portion of the reaction mixture, and the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from greater than 2,000 to about 10,000. In a preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 3,000 to about 7,000. In a more preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 5,000 to about 7,000. The biocompatible membrane of the invention can be the product of a mixture having a glucose diffusion coefficient of from about 1 x 10 '~ cm2/s to about 200 x 10-'~ cm2/s at 37°C, or preferably, from about 2.5 x 10- cm'-/s to about 10 x 10- cmz/s at 37°C.
Polymer Blends The biocompatible membrane of the invention comprises a combination of hydrophobic (polysiloxane) and hydrophilic polymers. In a preferred embodiment, the hydrophilic polymer comprises polyurea (see, e.g., U.S. Patent Nos. 5,777,060 and 5,786,439, both of which are incorporated herein by reference) and, optionally, polyurethane as well. The membrane preferably includes a blend of two or more polymers, each of which can comprise a combination of two or more polymers with different characteristics, including combinations of hydrophobic and hydrophilic polymers, yielding a solid mixture or blend with desired glucose limiting and performance properties.
In one embodiment, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol. A preferred diamino terminated copolymer of polypropylene glycol and polyethylene glycol, comprises polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether).
Suitable hydrophilic polymers for use in polymer blends of the invention have average molecular weights in the range of from about 400 to about 2000, and include polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ethers QeffamineTM;
Huntsman Chemical) such as Jeffamine 600 QG00), having an average molecular weight (mw) of 600, and Jeffamine 900 Q900), having an average mw of 900; polyethylene glycols (PEGS), such as PEG having an average mw of 600, 1000 or 2000 (1'EG 600, PEG
1000, PEG 2000); polypropylene glycols (PPGs), such as PPG having an average mw of 400;
and diamino polyethylene glycol (DAPEG), such as DAPEG 2000, having an average mw of 2000.
In a preferred embodiment, the polysiloxane content is from about 15 mole% to about 75 mole % of the polymeric portion of the mixture, or more preferably, about 50 mole % of the polymeric portion of the mixture. A preferred polysiloxane has a molecular weight of about 500 to about 3,500, with a molecular weight of about 2,500 being most preferable. In one embodiment, the hydrophilic polymer comprises a combination of J600 and J900. In another embodiment, the polymeric portion of the mixture comprises about 50 mole % polysiloxane, about 25 mole % hydrophilic polymer having an average molecular weight of about 600, and about 25 mole %
hydrophilic polymer having an average molecular weight of about 900. Preferably, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, such as polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether) QeffamineTl''~. Exemplary polymeric compositions for use in the reaction mixture of the invention and their permeability characteristics are described in Table 1 (wherein "hp" refers to hydrophilic portion). Additional preferred polymer combinations and their influence on sensor characteristics axe described in Table 2.
Table 1 Desig-CompositionHydration DiffusionIntrinsicnA SignalRZ Thick-@100 nation CoefficientViscositymg/dL Min- ness (mm*h)(mL/g) Max (gym) x 10e-6 (nA) Initial %
Rate Max m /min 75/25 29 37 0.82 30 25-39 22- 0.997-2.7 600/PS510 G2 0.999 936-5385/15 52.5 4G 1.G4 20 70.1 59- 0.998 1.G
936-11hp-75/2523 32 0.59 35 39.2 35.5-1 3.8 600/P600 42.4 936-15hp-100 97 54 15.5 50 195.8 149- 0.974 2.3 936-22hp-75/2528.5 43 2.7G 38 G4 G0.7-0.999 3.G
G00/ 71.5 93G-42hp-90/1068.5 35 1.7 21 42.8 39.1-0.998 2.8 600/ 47.1 985-G7hp-85/1558 42 1.67 26 68.6 65-720.999 2.2 985-2335/20/4511 5 0.24 46 23.6 23.3-1 2.6 JG00/J900/ 24.1 985-7975/25 51.5 38 1.33 16 49.2 43.5-0.997 1.9 JG00/PS510 56.6 w/ EDA
Extension 2% Blend49 30 1.09 N/A 3G.1 29.9-0.999 2.5 of 75/25 46.1 w/
h - 100 5% Blend56.5 31.6 1.56 N/A 54.2 42.3-0.999 2.1 7G.6 11% Blend62 31.9 1.32 N/A 49 44-550.998 2.2 15% Blend60 37.3 1.52 N/A 58.8 54-620.998 2.3 20% Blend65 36.7 1.92 N/A 57.6 32.4-0.993 2.3 G9.9 1001- 50/50 280.9 52 38.4 36 39 DAPEG2ooo 2% Blend51 28.5 36.3 34-401 2.6 of 75/25 w/ 1/1 DAPEG
5% Blend54 21.5 43.5 41-450.999 2.5 15% Blend58 11.7 61.9 58-670.999 2.5 927- h :50% 15 37 0.06 46 12 10 0.999 1.8 to 34 a G00 14 927-40hp:50% 77 98 9.23 39 103 100 0.997 un-peg1000 to even 927-43hp:50% GO 47 3.88 40 13G 117 0.993 1.8 jeff900 to 927-4880% jeffG0052 39 2.32 23 32 28 0.998 2.5 to 927-52hp:25% 24 21 0.54 31 2G 23 0.999 1.7 to 0.47 927-54hp:50% 10 12 0.04 23 G 7 0.978 4.1 to 98G-17G5% jeffG0022 20 0.22 32 18 17 0.999 3.2 to 98G-49nmda/ 38 29 0.79 27 24 23 0.999 2.9 to extension 25 98G-G310% excess42 31 0.79 20 2G 25 0.998 3.4 to hmdi 35 Table 1 ,continued Desig-CompositionTheta Theta (air) (AI) nation Dry HydratedPost- Dry HydratedPost-h dration h dration Production Material 936-5385/15 109.197.9 106.8 113.195.3 104.2 93G-11hp-75/25 100.198.G 107.8 103.4105.3 109.8 93G-15hp-100 93G-22hp-75/25 93G-42hp-90/10 985-G7hp-85/15 103.9106.2 105 112 109.1 108.7 985-2335/20/45 93.G 105.4 985-79Production108.1105.9 111.4106.2 Ration w/
EDA
Extension 2% Blend of Production w/ h -5% Blend 11% Blend 15% Blend 20% Blend 107.2105.2 93.8 102.7 1001-50/50 109.179.3 105.4 103.551.2 105.4 3~ DAI'T'G2000/
Table 2 Oxygen Glucose Oa/ Percent Change Poly-Membrane Perm- Perm- Glucosein Glucose mer Com eabilityeabilityPerm- permeability osition (cm2/s) (cm2/s) eability x 10-5 x 10-9 Ratio from C
Jeff Jeff 27 C 42 C
s 900 600 (high) (low) lox-ane A 50% 50% 2.9 27 1074 18% -19%
Below B 50% 50% 2.0 detectionN/A
limit C 50% 25% 25% 2.3 4.4 5227 41% -15%
Below D 75% 25% 2.2 detectionN/A
limit E 25% 75% 1 5.0 2000 64% -42%
As shown in Table 2, glucose permeability is more affected than oxygen permeability by changing the characteristics of the hydrophilic component. In these examples, the hydrophilic component is altered by varying the relative amounts of J600 and J900, the latter of which is more hydrophilic than J600 by virtue of its greater molecular weight. Polymer C is an illustration of how these trends can be used to tailor glucose and oxygen permeabilities. This material has the same fractional amount of polysiloxane (PS) therefore maintaining good oxygen permeation. The hydrophilicity of the polymer has been reduced (relative to a J900-PS polymer) by using equimolar amounts of J900 and J600. Because the hydrophilicity has been decreased without compromising the oxygen permeability of the polymer to a great extent, a material with a superior oxygen/glucose permeability ratio is obtained.
Because the temperature of adipose tissue surrounding a subcutaneous glucose sensor could be expected to range from roughly 30 to 40°C, a polymer whose glucose permeability is unaffected by temperature is desirable. Table 2 details the change in glucose permeability (%) observed when cooling the sensor from 37°C to 27 °C or warming the sensor to 42 °C from 37 °C. Interestingly, glucose permeability drops with increasing temperature, whereas oxygen permeability increases with temperature.
The inverse relationship between glucose permeability and temperature is believed to be the result of the known lower critical solution temperature (LCST) of many water-soluble polyethers such as JeffamineTM 600 and JeffamineTM 900. The LCST
of aqueous solutions of these polymers is manifested by the fact that these polymers axe less soluble in water at higher temperatures. Previous data have shown that glucose permeability improves with increasing membrane hydrophilicity. Therefore, if higher temperatures result in a less hydrated membrane due to the LCST
characteristics of the polyether segments of the membrane, glucose permeability would also be lessened at higher temperatures.
The data in the table below suggest materials with smaller fractional polyether compositions are less subject to changes in glucose permeability with changes in temperature. Furthermore, polymers with higher JeffamineTM 900 content in their hydrophilic portion appear to have glucose permeabilities that are less susceptible to changing temperature.
A polymer with greater than 50% PS content would be beneficial due to the increased oxygen permeability and its reduced susceptibility to temperature modulated glucose permeability. However, the decreased hydrophilicity should be offset with the addition of more JeffamineTM 900 than JeffamineTM 600, as the former promotes glucose permeability better than the latter and appears to be less sensitive to thermal changes.
Polymer D, 75% PS-25% Jeff 900, did not show any glucose permeability (OZ
permeability was not measured). This suggests that the PS content is best kept below about 75%. A material comprising 60% PS and 40% Jeff 900 (F~ may offer advantageous properties. Additionally, 60% 1'S-30% Jeff 900-10% Jeff 600 (G) would be an additional attractive alternative. Other alternatives that should yield similar results include polymers incorporating polyethylene glycol (1'EG), polypropylene glycol (PPG), amino-terminated PEG or PPG, as well as polymeric blends of the polymers incorporating the above components, block copolymers generated from the above components or blends of the above monomers to yield random copolymeric structures.
In addition to the hydrophilic and hydrophobic polymers described above, the reaction mixture comprises a diisocyanate, which constitutes about 50 mole %
of the reaction mixture. Examples of diisocyanates include hexamethylene-1,6-diisocyanate (HMDI), dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate.
In some embodiments, 10% excess HMDI is included in the reaction mixture. In some embodiments, the reaction mixture further comprises a chain extender, such as N-methyl diethanolamine (NMDA), ethylene diamine (EDA) or water (H20).
Factors useful in selecting a polymeric composition for use in a biocompatible membrane of the invention include hydration rate, diffusion coefficient, and sensor performance and linearity. Preferred compositions have an initial hydration rate (mg/min for a 5 minute period) at least equal to 29, a diffusion coefficient at least equal to 0.82 x 10-~ mm h, and sensor performance in 100 mg/dL glucose solution of between 20 and 70 n.A (more preferably between 25 and 30 nA) with membrane thickness' (as measured by reflectometry from a gold plated glass slide coated under the same conditions as the sensors) that will allow for increasing coating thickness in the case of high readings, and reducing thickness in the case of low readings.
Biosensor Biosensors typically include a transducer that generates a signal upon contact with an analyte of interest. ror example, glucose sensors suitable for in vivo use can be prepared by depositing a glucose sensitive enzyme, such as glucose oxidase, onto an electrode via an electromotive plating process. The substrate can be applied by immersion of the sensor in a bath comprising glucose oxidase, a stabilizing protein, a surfactant and a buffer for conductivity and stability of the protein solution, and the enzyme is then deposited onto the electrode potentiometrically. Alternatively, the substrate can be applied using a microelectrogravimetric plating method, such as is described in U.S. patent application number 09/642,623.
The invention provides an implantable biosensor fox measuring an analyte of interest in biological tissue, the biosensor having a coating comprising a biocompatible membrane of the invention. The implantable biosensox can further comprise a transducer that generates a signal upon contact with the analyte. In a preferred embodiment, the analyte is glucose and the transducer is glucose oxidase.
Other enzymes can serve as transducers as appropriate for the analyte of interest and examples of such enzymes include, but are not limited to, lactate oxidase, amino acid oxidase, glutathione, and reductase.
Methods The invention additionally provides a method of measuring an analyte in a tissue of a subject. The method comprises introducing an implantable biosensor of the invention into the tissue of the subject, and detecting the signal generated by the transducer. The amount of signal corresponds to the amount of analyte.
Preferably, the analyte is glucose and the transducer is glucose oxidase.
The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure.
Merely by way of example a variety of solvents, membrane formation methods, and other materials may be used without departing from the scope of the invention.
The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.
All publications, patents and patent applications mentioned in this specification are herein incorporated by reference into the specification to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference.
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to polymeric materials and to methods of making and using such materials. The polymeric materials are hydrophilic, biocompatible, and suitable for use with biosensors, such as glucose sensors.
BACKGROUND OF THE INVENTION
Biosensors are small devices that use biological recognition properties for selective detection of various analytes or biomolecules. Typically, the sensor will produce a signal that is quantitatively related to the concentration of the analyte. To achieve a quantitative signal, a recognition molecule or combination of molecules is often immobilized at a suitable transducer, which converts the biological recognition event into a quantitative response.
The need for the continuous monitoring of biological markers (analytes) in medicine has sparked a tremendous interest in the study of biosensors in recent years.
Without question, the greatest interest has been geared toward the development of sensors to detect glucose. In particular, enzymatic (amperometzic) glucose electrodes have been studied in more detail than any other biosensors. Electroenzymatic biosensors use enzymes to convert a concentration of analyte to an electrical signal.
Immunological biosensors rely on molecular recognition of an analyte by, for example, antibodies. Chemoreceptor biosensors use chemoreceptor arrays such as those of the olfactory system or nerve fibers from the antennules of the blue crab Callinectes sapidus to detect the presence of amino acids in concentrations as low as 10v M. For a review of some of the operating principles of biosensors, see Bergveld, et al., Advances in Biosensors, Supplement 1, p. 31-91, Turner ed., and Collison, et al., Anal.
Chem. 62:425-437 (1990).
Regardless of the type of biosensor, each will possess certain properties to function in viva and provide an adequate signal. First, the elements of the biosensor should be compatible with the tissue to which it is attached, and be adequately safe such that allergic or toxic effects are not exerted. Further, the sensor should be shielded from the environment to control drift in the generated signal. Finally, the sensor should accurately measure the analyte in the presence of proteins, electrolytes and medications, which may have the potential to interfere.
The biosensor of interest is an amperometric glucose sensor. There are several reasons for the wide-ranging interest in glucose sensors. In the healthcare arena, enzymatic glucose test strips are useful for monitoring the blood sugar of patients with diabetes mellitus. A sensor that has the ability to continuously monitor the blood, or interstitial glucose of a person with diabetes could provide great insight into the level of control that they have over their disease and avoid the need fox repeated blood draws.
Additionally, a continuously monitoring glucose sensor is one of the critical components necessary for the development of an artificial pancreas. To make such a system possible, a reliable glucose sensor must communicate with an insulin pump.
An additional commercial application of this technology focuses on sensors that can be used to monitor fermentation reactions in the biotechnology industry.
From a scientific and commercial standpoint, interest has grown beyond glucose to other analytes for the diagnosis of numerous medical conditions other than diabetes.
Amperometric glucose sensors and oxido-reductase enzymes that use 02 as a co-substrate, and are designed for subcutaneous or intravenous use, typically require both an outer membrane and an anti-interference membrane. The necessity for two distinct membranes is largely due to the fundamental nature of the sensor, as well as the environment in which the measurement is made.
A glucose sensor works by a reaction in which glucose reacts with oxygen in the presence of glucose oxidase (GOd) to form gluconolactone and hydrogen peroxide. The gluconolactone further reacts with water to hydrolyze the lactone ring and produce gluconic acid. The H20z formed is electrochemically oxidized at an electrode as shown below (Equation 1):
HzOz -~ Oz +2e- +2H+ (I) The current measured by the sensor/potentiostat (+0.5 to +0.7 v oxidation at Pt black electrode) is the result of the two electrons generated by the oxidation of the HzOz.
Alternatively, one can measure the decrease in the oxygen by amperometric measurement (-0.5 to -1 V reduction at a Pt black electrode).
The stoichiometty of the GOd reaction points to a challenge of developing a reliable glucose sensor. If oxygen and glucose are present in equimolar concentrations, then the HZOz is stoichiometrically related to the amount of glucose that reacts at the enzyme. In this case, the ultimate current is also proportional to the amount of glucose that reacts with the enzyme. If there is insufficient oxygen for all of the glucose to react with the enzyme, then the current will be proportional to the oxygen concentration, not the glucose concentration. For the sensor to be a true glucose sensor, glucose must be the limiting reagent, i.e. the Oz concentration must be in excess for all potential glucose concentrations. For example, the glucose concentration in the body of a diabetic patient can vary from 2 to 30 mM (millimoles per liter or 36 to 540 mg/dl), whereas the typical oxygen concentration in the tissue is 0.02 to 0.2 mM (see, Fisher, et al., Biomed.
Biochem. Acta. 48:965-971 (1989). This ratio in the body means that the sensor would be running in the Michaelis Menten limited regime and would be very insensitive to small changes in the glucose concentration. This problem has been called the "oxygen deficit problem". Accordingly, a method ox system must be devised to either increase the Oz in the GOd enzyme layer, decrease the glucose concentration, or devise a sensor that does not use Oz.
There is a need fox a glucose sensor having a biocompatible membrane with an improved ratio of its oxygen permeability to it glucose permeability, and that offers physical and biological stability and strength, adhesion to the substrate, processibility (i.e.
solubility in common organic solvents for the development of coatings from polymer lacquer and the ability to cut using laser ablation or other large scale processing method), the ability to be synthesized and manufactured in reasonable quantities and at reasonable prices, , and compatibility with the enzyme as deposited on the sensor. The present invention fulfills these needs and provides other related advantages.
SUMMARY OF THE INVENTION
The invention provides a biocompatible membrane comprising a hydrophilic polyurea composition. The hydrophilic polyuxea composition comprises the product of a reaction mixture comprising (a) an amino terminated polysiloxane, (b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of 1o polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000, and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture. In this mixture, 15 (a) and (b) constitute a polymeric portion of the reaction mixture, and when the mixture is reacted with (c), the end product polymer has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 2,000 to about 10,000. In a preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 3,000 to 20 about 7,000. In a more preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 5,000 to about 7,000.
The biocompatible membrane of the invention can include a hydrophilic polymer that comprises a poly(pxopylene glycol)-block-polyethylene glycol) bis(2-aminopxopyl 25 ether). The polysiloxane preferably has a molecular weight of about 500 to about 3,500, and most preferably, about 2,500. In some embodiments, the reaction mixture further comprises a chain extender, such as N-methyl diethanolamine, ethylene diamine, butane diol, diethylene glycol, propane diol or water. The biocompatible membrane of the invention can be the product of a mixture having a glucose diffusion coefficient of from about 1 x 10-'~ cm2/s to about 200 x 10 '' cm2/s at 37°C, or preferably, from about 2.5 x 10v cm2/s to about 10 x 10v cmz/s at 37°C.
In a preferred embodiment, the polysiloxane content is from about 15 mole percent to about 75 mole percent of the polymeric portion of the mixture, or more preferably, about 50 mole percent of the polymeric portion of the mixture. In one embodiment, the hydrophilic polymer comprises a combination of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 600 and a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 900. In another embodiment, the polymeric portion of the mixture comprises about 50 mole percent polysiloxane, about 25 mole percent hydrophilic polymer having an average molecular weight of about 600, and about 25 mole percent hydrophilic polymer having an average molecular weight of about 900. Preferably, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol. A
preferred diamino terminated copolymer of polypropylene glycol and polyethylene glycol is polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether).
The invention further provides an implantable biosensor for measuring an analyte in biological tissue, the biosensor having a coating comprising a biocompatible membrane of the invention. The implantable biosensor can further comprise a transducer that generates a signal upon contact with the analyte. In a preferred embodiment, the analyte is glucose and the transducer is glucose oxidase.
The invention additionally provides a method of measuring an analyte in a tissue of a subject. The method comprises introducing an implantable biosensor of the invention into the tissue of the subject, and detecting the signal generated by the transducer. The amount of signal corresponds to the amount of analyte.
Preferably, the analyte is glucose and the transducer is glucose oxidase.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 is a schematic illustration of polymer formation using water as a chain extender and starting with a polyol diamine, a polysiloxane diamine and hexamethylene diisocyanate.
DETAILED DESCRIPTION
All scientific and technical terms used in this application have meanings commonly used in the art unless otherwise specified. As used in this application, the following words or phrases have the meanings specified.
As used herein, the term "polyurea" refers to a polymer containing urea linkages.
Such polymers may additionally contain urethane linkages. Typically, such polymers are formed by combining diisocyanates with amines and/or alcohols. For example, combining isophorone diisocyanate with PEG 600 and aminopropyl polysiloxane under polymerizing conditions provides a polyurethane/polyurea composition having both urethane (carbamate) linkages and urea linkages.
As used herein, "adhered to" or "adhered thereto" means stuck to or fused with such that a substance adhered to a surface remains substantially attached to or closely associated with the surface.
As used herein, "a" or "an" means at least one, and unless clearly indicated otherwise, includes a plurality.
Overview The invention provides hydrophilic glucose limiting polymeric materials that offer improved hydration and faster response times. The superior hydration characteristics of the polymeric materials provide improved biocompatibility and resistance to biofouling. The increased hydrophilicity of the material provides a polymer that can be coated onto a biosensor without requiring a second coating to enhance surface wetting of the device. In addition, the invention offers polymeric materials whose overall polymeric structure can be controlled by use of a diamine or diol chain extender instead of water. The invention additionally provides polymer blends that offer advantageous features over individual polymeric materials that can be selected in accordance with desired characteristics. Also provided are biosensors having a biocompatible membrane of the invention adhered thereto, and methods of measuring an analyte in a tissue of a subject using such a biosensor.
Three characteristics of the biocompatible membranes of the invention that are of particular interest axe glucose permeability, oxygen permeability, and the thermal dependence of these permeabilities. A preferred membrane has a permeability constant for glucose mass transport through the material that approximates 5.0 x 10-cmz/s at 37°C. Additionally, a ratio of oxygen permeability to glucose permeability of greater than about 3000 is preferred. Generally, the higher the permeability ratio, the better, with the exception of a ratio of infinity, which would result from a glucose permeability approaching zero. Also preferred is a membrane that exhibits minimal change in oxygen and glucose permeability in response to temperature changes.
Biocom~atible Membranes A glucose sensor intended for in vivo use requires that the supply of oxygen in the vicinity of the sensing element not be depleted. Additionally, the glucose should diffuse to the sensor at a controlled rate. Overall, the membrane should control the relative rates of diffusion of oxygen and glucose to the sensor so that the local concentration of oxygen is not depleted. Additionally, glucose sensors intended for in vivo use must also be biocompatible with the body, and they must be able to function in an environment in which harsh inflammatory components brought on by the process of tissue injury and healing are present. Furthermore, these membranes must resist against the adhesion of biological components (biofouling) such as cells and proteins that can interfere with a sensor's performance. Thus, the enzymes) used in such sensors must be protected from degradation or denaturation, while the elements of such sensors must be protected from molecules that would foul the sensors or their accuracy will decrease over time.
In one aspect, the present invention provides a biocompatible membrane comprising a hydrophilic polyurea composition. The hydrophilic polyurea composition comprises the product of a reaction mixture comprising (a) an amino terminated polysiloxane, (b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000, and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture. In this mixture, (a) and (b) constitute a polymeric portion of the reaction mixture, and the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from greater than 2,000 to about 10,000. In a preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 3,000 to about 7,000. In a more preferred embodiment, the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 5,000 to about 7,000. The biocompatible membrane of the invention can be the product of a mixture having a glucose diffusion coefficient of from about 1 x 10 '~ cm2/s to about 200 x 10-'~ cm2/s at 37°C, or preferably, from about 2.5 x 10- cm'-/s to about 10 x 10- cmz/s at 37°C.
Polymer Blends The biocompatible membrane of the invention comprises a combination of hydrophobic (polysiloxane) and hydrophilic polymers. In a preferred embodiment, the hydrophilic polymer comprises polyurea (see, e.g., U.S. Patent Nos. 5,777,060 and 5,786,439, both of which are incorporated herein by reference) and, optionally, polyurethane as well. The membrane preferably includes a blend of two or more polymers, each of which can comprise a combination of two or more polymers with different characteristics, including combinations of hydrophobic and hydrophilic polymers, yielding a solid mixture or blend with desired glucose limiting and performance properties.
In one embodiment, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol. A preferred diamino terminated copolymer of polypropylene glycol and polyethylene glycol, comprises polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether).
Suitable hydrophilic polymers for use in polymer blends of the invention have average molecular weights in the range of from about 400 to about 2000, and include polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ethers QeffamineTM;
Huntsman Chemical) such as Jeffamine 600 QG00), having an average molecular weight (mw) of 600, and Jeffamine 900 Q900), having an average mw of 900; polyethylene glycols (PEGS), such as PEG having an average mw of 600, 1000 or 2000 (1'EG 600, PEG
1000, PEG 2000); polypropylene glycols (PPGs), such as PPG having an average mw of 400;
and diamino polyethylene glycol (DAPEG), such as DAPEG 2000, having an average mw of 2000.
In a preferred embodiment, the polysiloxane content is from about 15 mole% to about 75 mole % of the polymeric portion of the mixture, or more preferably, about 50 mole % of the polymeric portion of the mixture. A preferred polysiloxane has a molecular weight of about 500 to about 3,500, with a molecular weight of about 2,500 being most preferable. In one embodiment, the hydrophilic polymer comprises a combination of J600 and J900. In another embodiment, the polymeric portion of the mixture comprises about 50 mole % polysiloxane, about 25 mole % hydrophilic polymer having an average molecular weight of about 600, and about 25 mole %
hydrophilic polymer having an average molecular weight of about 900. Preferably, the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, such as polypropylene glycol)-block-polyethylene glycol) bis(2-aminopropyl ether) QeffamineTl''~. Exemplary polymeric compositions for use in the reaction mixture of the invention and their permeability characteristics are described in Table 1 (wherein "hp" refers to hydrophilic portion). Additional preferred polymer combinations and their influence on sensor characteristics axe described in Table 2.
Table 1 Desig-CompositionHydration DiffusionIntrinsicnA SignalRZ Thick-@100 nation CoefficientViscositymg/dL Min- ness (mm*h)(mL/g) Max (gym) x 10e-6 (nA) Initial %
Rate Max m /min 75/25 29 37 0.82 30 25-39 22- 0.997-2.7 600/PS510 G2 0.999 936-5385/15 52.5 4G 1.G4 20 70.1 59- 0.998 1.G
936-11hp-75/2523 32 0.59 35 39.2 35.5-1 3.8 600/P600 42.4 936-15hp-100 97 54 15.5 50 195.8 149- 0.974 2.3 936-22hp-75/2528.5 43 2.7G 38 G4 G0.7-0.999 3.G
G00/ 71.5 93G-42hp-90/1068.5 35 1.7 21 42.8 39.1-0.998 2.8 600/ 47.1 985-G7hp-85/1558 42 1.67 26 68.6 65-720.999 2.2 985-2335/20/4511 5 0.24 46 23.6 23.3-1 2.6 JG00/J900/ 24.1 985-7975/25 51.5 38 1.33 16 49.2 43.5-0.997 1.9 JG00/PS510 56.6 w/ EDA
Extension 2% Blend49 30 1.09 N/A 3G.1 29.9-0.999 2.5 of 75/25 46.1 w/
h - 100 5% Blend56.5 31.6 1.56 N/A 54.2 42.3-0.999 2.1 7G.6 11% Blend62 31.9 1.32 N/A 49 44-550.998 2.2 15% Blend60 37.3 1.52 N/A 58.8 54-620.998 2.3 20% Blend65 36.7 1.92 N/A 57.6 32.4-0.993 2.3 G9.9 1001- 50/50 280.9 52 38.4 36 39 DAPEG2ooo 2% Blend51 28.5 36.3 34-401 2.6 of 75/25 w/ 1/1 DAPEG
5% Blend54 21.5 43.5 41-450.999 2.5 15% Blend58 11.7 61.9 58-670.999 2.5 927- h :50% 15 37 0.06 46 12 10 0.999 1.8 to 34 a G00 14 927-40hp:50% 77 98 9.23 39 103 100 0.997 un-peg1000 to even 927-43hp:50% GO 47 3.88 40 13G 117 0.993 1.8 jeff900 to 927-4880% jeffG0052 39 2.32 23 32 28 0.998 2.5 to 927-52hp:25% 24 21 0.54 31 2G 23 0.999 1.7 to 0.47 927-54hp:50% 10 12 0.04 23 G 7 0.978 4.1 to 98G-17G5% jeffG0022 20 0.22 32 18 17 0.999 3.2 to 98G-49nmda/ 38 29 0.79 27 24 23 0.999 2.9 to extension 25 98G-G310% excess42 31 0.79 20 2G 25 0.998 3.4 to hmdi 35 Table 1 ,continued Desig-CompositionTheta Theta (air) (AI) nation Dry HydratedPost- Dry HydratedPost-h dration h dration Production Material 936-5385/15 109.197.9 106.8 113.195.3 104.2 93G-11hp-75/25 100.198.G 107.8 103.4105.3 109.8 93G-15hp-100 93G-22hp-75/25 93G-42hp-90/10 985-G7hp-85/15 103.9106.2 105 112 109.1 108.7 985-2335/20/45 93.G 105.4 985-79Production108.1105.9 111.4106.2 Ration w/
EDA
Extension 2% Blend of Production w/ h -5% Blend 11% Blend 15% Blend 20% Blend 107.2105.2 93.8 102.7 1001-50/50 109.179.3 105.4 103.551.2 105.4 3~ DAI'T'G2000/
Table 2 Oxygen Glucose Oa/ Percent Change Poly-Membrane Perm- Perm- Glucosein Glucose mer Com eabilityeabilityPerm- permeability osition (cm2/s) (cm2/s) eability x 10-5 x 10-9 Ratio from C
Jeff Jeff 27 C 42 C
s 900 600 (high) (low) lox-ane A 50% 50% 2.9 27 1074 18% -19%
Below B 50% 50% 2.0 detectionN/A
limit C 50% 25% 25% 2.3 4.4 5227 41% -15%
Below D 75% 25% 2.2 detectionN/A
limit E 25% 75% 1 5.0 2000 64% -42%
As shown in Table 2, glucose permeability is more affected than oxygen permeability by changing the characteristics of the hydrophilic component. In these examples, the hydrophilic component is altered by varying the relative amounts of J600 and J900, the latter of which is more hydrophilic than J600 by virtue of its greater molecular weight. Polymer C is an illustration of how these trends can be used to tailor glucose and oxygen permeabilities. This material has the same fractional amount of polysiloxane (PS) therefore maintaining good oxygen permeation. The hydrophilicity of the polymer has been reduced (relative to a J900-PS polymer) by using equimolar amounts of J900 and J600. Because the hydrophilicity has been decreased without compromising the oxygen permeability of the polymer to a great extent, a material with a superior oxygen/glucose permeability ratio is obtained.
Because the temperature of adipose tissue surrounding a subcutaneous glucose sensor could be expected to range from roughly 30 to 40°C, a polymer whose glucose permeability is unaffected by temperature is desirable. Table 2 details the change in glucose permeability (%) observed when cooling the sensor from 37°C to 27 °C or warming the sensor to 42 °C from 37 °C. Interestingly, glucose permeability drops with increasing temperature, whereas oxygen permeability increases with temperature.
The inverse relationship between glucose permeability and temperature is believed to be the result of the known lower critical solution temperature (LCST) of many water-soluble polyethers such as JeffamineTM 600 and JeffamineTM 900. The LCST
of aqueous solutions of these polymers is manifested by the fact that these polymers axe less soluble in water at higher temperatures. Previous data have shown that glucose permeability improves with increasing membrane hydrophilicity. Therefore, if higher temperatures result in a less hydrated membrane due to the LCST
characteristics of the polyether segments of the membrane, glucose permeability would also be lessened at higher temperatures.
The data in the table below suggest materials with smaller fractional polyether compositions are less subject to changes in glucose permeability with changes in temperature. Furthermore, polymers with higher JeffamineTM 900 content in their hydrophilic portion appear to have glucose permeabilities that are less susceptible to changing temperature.
A polymer with greater than 50% PS content would be beneficial due to the increased oxygen permeability and its reduced susceptibility to temperature modulated glucose permeability. However, the decreased hydrophilicity should be offset with the addition of more JeffamineTM 900 than JeffamineTM 600, as the former promotes glucose permeability better than the latter and appears to be less sensitive to thermal changes.
Polymer D, 75% PS-25% Jeff 900, did not show any glucose permeability (OZ
permeability was not measured). This suggests that the PS content is best kept below about 75%. A material comprising 60% PS and 40% Jeff 900 (F~ may offer advantageous properties. Additionally, 60% 1'S-30% Jeff 900-10% Jeff 600 (G) would be an additional attractive alternative. Other alternatives that should yield similar results include polymers incorporating polyethylene glycol (1'EG), polypropylene glycol (PPG), amino-terminated PEG or PPG, as well as polymeric blends of the polymers incorporating the above components, block copolymers generated from the above components or blends of the above monomers to yield random copolymeric structures.
In addition to the hydrophilic and hydrophobic polymers described above, the reaction mixture comprises a diisocyanate, which constitutes about 50 mole %
of the reaction mixture. Examples of diisocyanates include hexamethylene-1,6-diisocyanate (HMDI), dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate.
In some embodiments, 10% excess HMDI is included in the reaction mixture. In some embodiments, the reaction mixture further comprises a chain extender, such as N-methyl diethanolamine (NMDA), ethylene diamine (EDA) or water (H20).
Factors useful in selecting a polymeric composition for use in a biocompatible membrane of the invention include hydration rate, diffusion coefficient, and sensor performance and linearity. Preferred compositions have an initial hydration rate (mg/min for a 5 minute period) at least equal to 29, a diffusion coefficient at least equal to 0.82 x 10-~ mm h, and sensor performance in 100 mg/dL glucose solution of between 20 and 70 n.A (more preferably between 25 and 30 nA) with membrane thickness' (as measured by reflectometry from a gold plated glass slide coated under the same conditions as the sensors) that will allow for increasing coating thickness in the case of high readings, and reducing thickness in the case of low readings.
Biosensor Biosensors typically include a transducer that generates a signal upon contact with an analyte of interest. ror example, glucose sensors suitable for in vivo use can be prepared by depositing a glucose sensitive enzyme, such as glucose oxidase, onto an electrode via an electromotive plating process. The substrate can be applied by immersion of the sensor in a bath comprising glucose oxidase, a stabilizing protein, a surfactant and a buffer for conductivity and stability of the protein solution, and the enzyme is then deposited onto the electrode potentiometrically. Alternatively, the substrate can be applied using a microelectrogravimetric plating method, such as is described in U.S. patent application number 09/642,623.
The invention provides an implantable biosensor fox measuring an analyte of interest in biological tissue, the biosensor having a coating comprising a biocompatible membrane of the invention. The implantable biosensox can further comprise a transducer that generates a signal upon contact with the analyte. In a preferred embodiment, the analyte is glucose and the transducer is glucose oxidase.
Other enzymes can serve as transducers as appropriate for the analyte of interest and examples of such enzymes include, but are not limited to, lactate oxidase, amino acid oxidase, glutathione, and reductase.
Methods The invention additionally provides a method of measuring an analyte in a tissue of a subject. The method comprises introducing an implantable biosensor of the invention into the tissue of the subject, and detecting the signal generated by the transducer. The amount of signal corresponds to the amount of analyte.
Preferably, the analyte is glucose and the transducer is glucose oxidase.
The above description is illustrative and not restrictive. Many variations of the invention will become apparent to those of skill in the art upon review of this disclosure.
Merely by way of example a variety of solvents, membrane formation methods, and other materials may be used without departing from the scope of the invention.
The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their full scope of equivalents.
All publications, patents and patent applications mentioned in this specification are herein incorporated by reference into the specification to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference.
Claims (23)
1. A biocompatible membrane comprising a hydrophilic polyurea composition comprising the product of a first reaction mixture comprising:
(a) an amino terminated polysiloxane;
(b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000; and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture;
wherein (a) and (b) constitute a polymeric portion of the first reaction mixture, and wherein the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from greater than 2,000 to about 10,000.
(a) an amino terminated polysiloxane;
(b) a hydrophilic polymer selected from the group consisting of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol, polyethylene glycol, polypropylene glycol and diamino polyethylene glycol having an average molecular weight of from about 400 to about 2000; and (c) a diisocyanate selected from the group consisting of hexamethylene-1,6-diisocyanate, dicyclohexylinethane 4,4'-diisocyanate, and isophorone diisocyanate, and constituting about 50 mole % of the reaction mixture;
wherein (a) and (b) constitute a polymeric portion of the first reaction mixture, and wherein the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from greater than 2,000 to about 10,000.
2. The biocompatible membrane of claim 1, wherein the hydrophilic polyurea composition further comprises the product of blend of the first reaction mixture and a second reaction mixture, wherein the second reaction mixture comprises (a), (b) and (c).
3. The biocompatible membrane of claim 1, wherein the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 3,000 to about 7,000.
4. The biocompatible membrane of claim 1, wherein the hydrophilic polyurea composition has a ratio of its diffusion coefficient for oxygen to its diffusion coefficient for glucose of from about 5,000 to about 7,000.
5. The biocompatible membrane of claim 1, wherein the hydrophilic polymer comprises a poly(propylene glycol)-block-poly(ethylene glycol) bis(2-aminopropyl ether).
6. The biocompatible membrane of claim 1, wherein the polysiloxane has a molecular weight of from about 500 to about 3,500.
7. The biocompatible membrane of claim 6, wherein the polysiloxane has a molecular weight of about 2,500.
8. The biocompatible membrane of claim 1, wherein the mixture further comprises a chain extender.
9. The biocompatible membrane of claim 8, wherein the chain extender is selected from the group consisting of N-methyl diethanolamine, ethylene diamine, butane diol, diethylene glycol, propane diol and water.
10. The biocompatible membrane of claim 1, wherein the mixture has a glucose diffusion coefficient of from about 1 x 10-9 cm2/s to about 200 x 10-9 cm2/s at 37°C.
11. The biocompatible membrane of claim 1, wherein the mixture has a glucose diffusion coefficient of from about 2.5 x 10-9 cm2/s to about 10 x 10-9 cm2/s at 37°C.
12. The biocompatible membrane of claim 1, wherein the polysiloxane content is from about 15 mole percent to about 75 mole percent of the polymeric portion of the mixture.
13. The biocompatible membrane of claim 1, wherein the polysiloxane content is about 50 mole percent of the polymeric portion of the mixture.
14. The biocompatible membrane of claim 1, wherein the hydrophilic polymer comprises a combination of a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 600;
and a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 900.
and a diamino terminated copolymer of polypropylene glycol and polyethylene glycol having an average molecular weight of about 900.
15. The biocompatible membrane of claim 14, wherein the diamino terminated copolymer of polypropylene glycol and polyethylene glycol comprises a poly(propylene glycol)-block-poly(ethylene glycol) bis(2-aminopropyl ether).
16. The biocompatible membrane of claim 1, wherein the polymeric portion of the mixture comprises about 50 mole percent polysiloxane, about 25 mole percent hydrophilic polymer having an average molecular weight of about 600, and about 25 mole percent hydrophilic polymer having an average molecular weight of about 900.
17. The biocompatible membrane of claim 16, wherein the hydrophilic polymer comprises a diamino terminated copolymer of polypropylene glycol and polyethylene glycol.
18. The biocompatible membrane of claim 17, wherein the diamino terminated copolymer of polypropylene glycol and polyethylene glycol comprises a poly(propylene glycol)-block-poly(ethylene glycol) bis(2-aminopropyl ether).
19. An implantable biosensor for measuring an analyte in biological tissue, the biosensor having a coating adhered thereto, the coating comprising a biocompatible membrane of claim 1.
20. The implantable biosensor of claim 19, further comprising a transducer that generates a signal upon contact with the analyte.
21. The implantable biosensor of claim 20, wherein the analyte is glucose and the transducer is glucose oxidase.
22. A method of measuring an analyte in a tissue of a subject, the method comprising introducing an implantable biosensor of claim 20 into the tissue of the subject and detecting the signal generated by the transducer, wherein the amount of signal corresponds to the amount of analyte.
23. The method of claim 22, wherein the analyte is glucose and the transducer is glucose oxidase.
Applications Claiming Priority (3)
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|---|---|---|---|
| US09/753,095 US6642015B2 (en) | 2000-12-29 | 2000-12-29 | Hydrophilic polymeric material for coating biosensors |
| US09/753,095 | 2000-12-29 | ||
| PCT/US2001/045506 WO2002053764A2 (en) | 2000-12-29 | 2001-10-25 | Hydrophilic polymeric material for coating biosensors |
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|---|---|
| CA2428610A1 true CA2428610A1 (en) | 2002-07-11 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002428610A Abandoned CA2428610A1 (en) | 2000-12-29 | 2001-10-25 | Hydrophilic polymeric material for coating biosensors |
Country Status (6)
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| US (1) | US6642015B2 (en) |
| EP (1) | EP1346000A2 (en) |
| JP (1) | JP2004517195A (en) |
| AU (1) | AU2002220075A1 (en) |
| CA (1) | CA2428610A1 (en) |
| WO (1) | WO2002053764A2 (en) |
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| JPS62102816A (en) | 1985-10-30 | 1987-05-13 | Agency Of Ind Science & Technol | Gas permselective membrane |
| US5214119A (en) * | 1986-06-20 | 1993-05-25 | Minnesota Mining And Manufacturing Company | Block copolymer, method of making the same, dimaine precursors of the same, method of making such diamines and end products comprising the block copolymer |
| US5045391A (en) * | 1990-02-23 | 1991-09-03 | Minnesota Mining And Manufacturing Company | Release coatings for dielectric substrates |
| US5593852A (en) | 1993-12-02 | 1997-01-14 | Heller; Adam | Subcutaneous glucose electrode |
| US5322063A (en) | 1991-10-04 | 1994-06-21 | Eli Lilly And Company | Hydrophilic polyurethane membranes for electrochemical glucose sensors |
| US5786439A (en) | 1996-10-24 | 1998-07-28 | Minimed Inc. | Hydrophilic, swellable coatings for biosensors |
| US5882494A (en) | 1995-03-27 | 1999-03-16 | Minimed, Inc. | Polyurethane/polyurea compositions containing silicone for biosensor membranes |
| US6355759B1 (en) * | 1996-04-25 | 2002-03-12 | 3M Innovative Properties Company | Polydiorganosiloxane polyurea segmented copolymers and a process for making same |
| AU7245796A (en) | 1996-09-26 | 1998-04-17 | Minimed, Inc. | Silicon-containing biocompatible membranes |
-
2000
- 2000-12-29 US US09/753,095 patent/US6642015B2/en not_active Expired - Lifetime
-
2001
- 2001-10-25 JP JP2002555269A patent/JP2004517195A/en active Pending
- 2001-10-25 EP EP01272550A patent/EP1346000A2/en not_active Withdrawn
- 2001-10-25 CA CA002428610A patent/CA2428610A1/en not_active Abandoned
- 2001-10-25 WO PCT/US2001/045506 patent/WO2002053764A2/en active Application Filing
- 2001-10-25 AU AU2002220075A patent/AU2002220075A1/en not_active Abandoned
Also Published As
| Publication number | Publication date |
|---|---|
| US6642015B2 (en) | 2003-11-04 |
| JP2004517195A (en) | 2004-06-10 |
| WO2002053764A2 (en) | 2002-07-11 |
| WO2002053764A3 (en) | 2002-10-17 |
| AU2002220075A1 (en) | 2002-07-16 |
| US20020123087A1 (en) | 2002-09-05 |
| EP1346000A2 (en) | 2003-09-24 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |