Thermally stable glucose limiting membrane for glucose sensors
Embodiments of the invention provide compositions useful in analyte sensors as well as methods for making and using such compositions and sensors. In typical embodiments of the invention, the sensor is a glucose sensor comprising an analyte modulating membrane formed from a polymeric reaction mixture formed to include limiting amounts of catalyst and/or polycarbonate compounds so as to provide such membranes with improved material properties such as enhanced thermal and hydrolytic stability.
1. A method of increasing the thermal stability of a biocompatible membrane formed by a reaction mixture comprising:
a diisocyanate;
a hydrophilic polymer comprising a hydrophilic diol or hydrophilic diamine;
a siloxane having an amino, hydroxyl or carboxylic acid functional group at a terminus;
a polycarbonate diol; and
a catalyst;
the method comprising forming the reaction mixture such that the catalyst is present in the reaction mixture in amounts less than 0.2% of reaction mixture components;
thereby increasing the thermal stability of the biocompatible membrane as compared to a comparable membrane formed from a reaction mixture where the catalyst is present in the reaction mixture in amounts greater than or equal to 0.2% of the reaction mixture; wherein:
the biocompatible membrane comprises:
from 17% to 23% weight percent hexamethylene diisocyanate;
from 0% to 8.5% weight percent methylene diphenyl diisocyanate;
from 14% to 48% weight percent polydimethylsiloxane having amino terminal groups; and
from 7.5% to 19% weight percent poly(1,6-hexyl carbonate) diol.
2. The method of claim 1 , wherein the catalyst is present in the reaction mixture in amounts less than 0.11% of the reaction mixture.
3. The method of claim 1 , wherein:
(a) the biocompatible membrane comprises:
about 22% hexamethylene diisocyanate; and
about 3.5% methylene diphenyl diisocyanate;
(b) the biocompatible membrane comprises about 22.5% polydimethylsiloxane having amino terminal groups; and
(c) the biocompatible membrane comprises about 7.5% poly(1,6-hexyl carbonate) diol.
4. The method of claim 1 , wherein water is added as a chain extender in the reaction mixture.
5. The method of claim 1 , wherein thermal stability of the biocompatible membrane is measured by observing changes in molecular weight of the biocompatible membrane maintained at a temperature of 60° C. over at least 3, 5 or 7 days.