Hydrophilic polyurethane membranes for electrochemical glucose sensors

DETAILED DESCRIPTION The primary requirement for an electrochemical glucose sensor intended for in vivo use is that the supply of oxygen in the vicinity of the sensing element not be depleted.
This does not mean that an electrochemical glucose sensor membrane need have an extremely high permeability to oxygen.
What is needed is a membrane that can moderate the diffusion of oxygen and glucose so that the local concentration of oxygen is not depleted.
It is sufficient if the ratio of the diffusion coefficient of oxygen to that of glucose is appropriate to the design of the glucose sensor.
Electrochemical glucose sensors intended for in vivo use must also be rendered biocompatible with the body, and they must be able to function in a hostile environment.
The enzyme(s) used in such sensors must be protected from degradation or denaturation.
At the same time, the sensing elements of such sensors must be protected from molecules which would foul the sensors or their accuracy will decrease over time.
The membranes of the present invention possess unique attributes that satisfy the above objectives.
Their properties can be varied to tailor their glucose and oxygen transport behavior to match the requirements of a particular configuration of an electrochemical glucose sensor.
The membranes of the present invention are particularly useful in the construction of electrochemical glucose sensors intended for in vivo use.
The homogeneous membranes of the invention are prepared from biologically acceptable polymers 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 electrochemical glucose sensors intended for in vivo use.
The membranes of the invention are fabricated from polymers prepared by the reaction of a diisocyanate, a poly(ethylene oxide), and an aliphatic diol.
The polymerization reaction may be carried out in solution or in bulk.
The preferred hydrophilic polyurethanes so produced are capable of absorbing from about 10 to about 50% of their weight of water, with those capable of absorbing from about 20% to about 30% of their weight of water being preferred