Silicone based membranes for use in implantable glucose sensors

Abstract

Membrane systems incorporating silicone polymers are described for use in implantable analyte sensors. Some layers of the membrane system may comprise a blend of a silicone polymer with a hydrophilic polymer, for example, a triblock poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) polymer. Such polymeric blends provide for both high oxygen solubility and aqueous analyte solubility.

What is claimed is: 
     
         1 . An implantable continuous analyte sensor, comprising:
 a working electrode; and   a membrane system disposed over at least a portion of the working electrode, the membrane system comprising a first domain and a second domain, the first domain and the second domain each comprising a blend comprising a silicone-containing polymer and a hydrophilic polymer, the first domain having a blend ratio of silicone-containing polymer to hydrophilic polymer that is different than a blend ratio of silicone-containing polymer to hydrophilic polymer of the second domain.   
     
     
         2 . The implantable continuous analyte sensor of  claim 1 , wherein the first domain is less permeable to an interfering species than to an analyte. 
     
     
         3 . The implantable continuous analyte sensor of  claim 1 , wherein the first domain is configured to provide a greater reduction of transport of an interfering species therethrough than the second domain. 
     
     
         4 . An implantable continuous analyte sensor, comprising:
 a working electrode; and   a membrane disposed over the working electrode, the membrane comprising:
 a first domain configured to have a greater selectivity for reducing permeability therethrough of a first interfering species than a second interfering species; 
 a second domain configured to have a greater selectivity for reducing permeability therethrough of a second interfering species than a first interfering species; and 
 a third domain comprising an enzyme configured to react with an analyte; and 
 wherein the first and second interfering species are molecules that would be electro-reduced or electro-oxidized by the working electrode if they reached an electroactive surface the working electrode. 
   
     
     
         5 . The implantable continuous analyte sensor of  claim 4 , wherein the first domain comprises a blend comprising a silicone-containing polymer and a hydrophilic polymer. 
     
     
         6 . The implantable continuous analyte sensor of  claim 4 , wherein the second domain comprises ionic components configured to reduce a permeability of the second domain to the second interfering species. 
     
     
         7 . The implantable continuous analyte sensor of  claim 4 , wherein the first interfering species is acetaminophen, and wherein the second interfering species is ascorbic acid. 
     
     
         8 . A method of manufacturing a membrane for use in an analyte sensor, the method comprising:
 mixing a precursor of a silicone elastomer with a poly(ethylene oxide) and poly(propylene oxide) co-polymer; and   heating the mixture.   
     
     
         9 . The method of  claim 8 , wherein a ratio of co-polymer to silicone elastomer that is mixed is from about 1:20 w/w to about 1:4 w/w. 
     
     
         10 . The method of  claim 8 , further comprising mixing the co-polymer with a cross-linking agent. 
     
     
         11 . The method of  claim 10 , wherein the cross-linking agent is mixed with the co-polymer prior to mixing the co-polymer with the silicone elastomer precursor. 
     
     
         12 . The method of  claim 10 , wherein the cross-linking agent is selected from the group consisting of one or more of ethylene glycol diglycidyl ether and poly(ethylene glycol) diglycidyl ether. 
     
     
         13 . The method of  claim 10 , wherein the cross-linking agent comprises dicumyl peroxide. 
     
     
         14 . The method of  claim 10 , wherein the ratio of cross-linking agent to co-polymer is from about 10 cross-linking agent molecules per co-polymer molecule to about 30 cross-linking agent molecules per co-polymer molecule. 
     
     
         15 . The method of  claim 10 , wherein the amount of cross-linking agent added relative to the silicone elastomer and co-polymer is from about 0.5% to about 15% w/w. 
     
     
         16 . The method of  claim 10 , further comprising, after the mixing step but before the heating step, drawing the mixture into a thin film. 
     
     
         17 . The method of  claim 16 , further comprising, after the drawing the mixture into the thin film but before the heating the mixture, placing a piece of porous silicon on the thin film.