Techniques to improve polyurethane membranes for implantable glucose sensors

Abstract

The invention provides an implantable membrane for regulating the transport of analytes therethrough that includes a matrix including a first polymer; and a second polymer dispersed throughout the matrix, wherein the second polymer forms a network of microdomains which when hydrated are not observable using photomicroscopy at 400× magnification or less. In one aspect, the homogeneous membrane of the present invention has hydrophilic domains dispersed substantially throughout a hydrophobic matrix to provide an optimum balance between oxygen and glucose transport to an electrochemical glucose sensor.

Description

RELATED APPLICATION [0001] This application is a division of application Ser. No. 10 / 153,356 filed May 22, 2002, the disclosure of which is hereby incorporated by reference in its entirety and is made a portion of this application.FIELD OF THE INVENTION [0002] The present invention relates generally to membranes for use in combination with implantable devices for evaluating an analyte in a body fluid. More particularly, the invention relates to membranes for controlling the diffusion of glucose therethrough to a glucose sensor. BACKGROUND OF THE INVENTION [0003] A biosensor is a device that uses biological recognition properties for the selective analysis of various analytes or biomolecules. Generally, the sensor will produce a signal that is quantitatively related to the concentration of the analyte. In particular, a great deal of research has been directed toward the development of a glucose sensor that would function in vivo to monitor a patient's blood glucose level. Such a gluc...

AI Technical Summary

Benefits of technology

[0016] The present invention provides an implantable membrane for controlling the diffusion of an analyte therethrough to a biosensor with which it is associated. In particular, the membrane of the present invention satisfies a need in the art by providing a homogenous membrane with both hydrophilic and hydrophobic regions to control the diffusion of glucose and oxygen to a biosensor, the membrane being fabricated easily and reproducibly from commercially available materials.

Problems solved by technology

Unfortunately, this requirement is not easily achieved.

As a consequence, oxygen can become a limiting reactant, giving rise to a problem with oxygen deficit.

One disadvantage of this invention is that the primary backbone structure of the polyurethane is sufficiently different so that more than one casting solvent may be required to fabricate the membranes.

This reduces the ease with which the membranes may be manufactured and may further reduce the reproducibility of the membrane.

Therefore, one skilled in the art cannot simply change the polymer composition and be able to predict the oxygen to glucose permeability ratios.

As a result, a large number of polymers would need to be synthesized before a desired specific oxygen to glucose permeability ratio could be obtained.

Moreover, as mentioned above, one skilled in the art cannot simply change the polymer composition and be able to predict the oxygen to glucose permeability ratios.

Therefore, a disadvantage of this membrane is that it can leach the surfactant over time and cause irritation at the implant site or change its permeability to glucose.

Repeatability of fabrication has been a problem associated with prior art membranes that attempt to regulate the transport of analytes to the sensing elements.

A disadvantage of the prior art membranes is that, upon thermodynamic separation from the hydrophobic portions, the hydrophilic components form undesirable structures that appear circular 1 and elliptical 2 when viewed with a light microscope when the membrane 3 is hydrated, but not when it is dry.

It is believed that these large domains present a problem in that they result in a locally high concentration of either hydrophobic or hydrophilic material in association with the electrode.

This can result in glucose diffusion being limited or variable across the dimension adjacent the sensing electrode.

Moreover, these large hydrated structures can severely limit the number of glucose diffusion paths available.

In this instance, glucose diffusion cannot adequately occur, or is severely limited across the dimension adjacent the electrode surface.

Consequently, one would expect that the locally high concentration of the hydrophobic regions adjacent to working electrode 30 would limit the ability of the sensing device to obtain accurate glucose measurements.

Again, the large non-uniform structures of the prior art membranes can limit the number of glucose diffusion paths and the ability of the sensing device to obtain accurate glucose measurements.

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