Implantable biosensor system, apparatus and method

Abstract

An implantable biosensor assembly and system includes an enzymatic sensor probe from which subcutaneous and interstitial glucose levels may be inferred. The assembly may be associated by direct percutaneous connection with electronics, such as for signal amplification, sensor polarization, and data download, manipulation, display, and storage. The biosensor comprises a miniature probe characterized by lateral flexibility and tensile strength and has a large electrode surface area for increased sensitivity. Irritation of tissues surrounding the probe is minimized due to ease of flexibility and small cross section of the sensor. Foreign body reaction is diminished due to a microscopically rough porous probe surface.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation of U.S. application Ser. No. 10 / 401,224, filed Mar. 26, 2003, the contents of the entirety of which are herein incorporated by this reference.TECHNICAL FIELD [0002] This invention relates generally to medical devices and associated methods such as measuring glucose for ongoing diabetes management. The invention described herein can also be used for enzymatic determination of other analytes. This invention provides a particularly useful implantable biosensor. BACKGROUND OF THE INVENTION [0003] Heretofore, treatment and management of diabetes has been undertaken through many and varied techniques. Formerly, glucose in urine was measured, though recognized as less than adequate due to the time delay inherent in the metabolism and voiding process. Currently, the approach predominantly used for self-monitoring of blood glucose requires periodic pricks of the skin with a needle, whereby a blood sample is obta...

AI Technical Summary

Benefits of technology

[0022] Desirably, an exterior coating of a negatively charged polymer is applied to the working electrode. One operable negatively charged polymer includes sulfonated polyethersulfone. It is also sometimes desirable to provide a microscopically roughed-up outer surface on the coating to enhance biocompatibility of the biosensor with tissue of the subject's body. Desirable surface texture is formed by elements having a size of between about 5 and 50 microns. Multifiber cores typically include a plurality of spaces between the fibers operable to carry glucose oxidase whereby to enhance a volume of glucose oxidase associated with a working electrode.

Problems solved by technology

Formerly, glucose in urine was measured, though recognized as less than adequate due to the time delay inherent in the metabolism and voiding process.

However, the dynamic nature of blood glucose chemistry and the complexity of factors influencing blood sugar levels render such periodic information less than optimal.

A deleterious impact on physiology follows either such disequilibrium.

Hypoglycemia, on the other hand, poses the more serious short-term danger.

Hypoglycemia can occur at any time of the day or night and can cause the patient to lose consciousness.

Guarding against hypoglycemia may require frequent monitoring of blood glucose levels and render the skin-prick approach tedious, painful and, in some cases, impractical.

Even diligent patients who perform finger-sticking procedures many times each day achieve only a poor approximation of continuous monitoring.

A risk of infection is associated with percutaneous biosensors, and they must typically be replaced at regular intervals because of the risk of infection at the insertion site.

Another problem with implanted sensors is irritation of the tissues surrounding the implanted biosensors.

Such irritation is typically due, in part, to the lateral rigidity of prior art biosensors.

Related to this problem is the scarring of surrounding tissue due not only to rigidity but also to abrupt edges associated with the implants.

However, scar tissue can be materially detrimental to the sensor function in the vicinity of the working electrode because it impedes the diffusion of oxygen and glucose.

Further, to protect itself against a perceived invader, the body commonly experiences a foreign body reaction by encapsulating the implanted biosensors with protein, which may shorten the life of the implant and adversely affect the accuracy of information provided.

The size of the sensor may also be regarded as a problem; smaller is better for comfort.

Further yet, interfering compounds, such as, for example, ascorbic acid, and acetaminophen, can reduce the accuracy of prior art amperometric glucose sensors given the membranes selected historically to envelop such sensors.

Additionally, the quantity of dissolved oxygen is limited at high glucose concentrations, thus leading to nonlinear output of sensor signals at high glucose concentrations.

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