Biocompatible, glucose-permeable hydrogel for in situ coating of implantable biosensors

A glucose-permeable hydrogel (97% water by mass) was formed by cross-linking an 8-armed, amine-terminated poly(ethylene glycol) (PEG) derivative with a di-succinimidyl ester of an alpha,omega-dipropionic acid derivative of PEG in aqueous solution at room temperature. The gel was evaluated as a biocompatible interface between an amperometric glucose electrode and the subcutaneous tissue of a rat. Over a glucose concentration range of 0-30 mM, the loss in sensitivity to glucose caused by the application of the hydrogel was 34% and the reduction in limiting current at high glucose concentration (30 mM) was 35% at 37 degrees C for films that were approximately 0.06 mm thick, an acceptable loss. Hydrogel and Pellethane samples were subcutaneously implanted in male Sprague-Dawley rats for 7 days. The explanted samples were thin-sectioned, stained and examined under a light microscope. While the Pellethane samples were encapsulated with tissue consisting of macrophages, neutrophils, foreign body giant cells, fibroblasts and collagen, the PEG samples had very few adherent cells. The results show this system to be a good candidate for providing biocompatible interfaces for sensors, especially oxidoreductase-based sensors.