BIOCOMPATIBILITY OF SILICON-BASED ELECTRODE ARRAYS IMPLANTED IN FELINE CORTICAL TISSUE

The passive biocompatibility of silicon-based electrode arrays was stu died in feline cortical tissue. Three types of arrays were used: uncoa ted, coated with polyimide, and coated with polyimide over an adhesion promoter. Fifteen arrays were implanted for 24 h to determine early t issue reaction to the implantation procedure, and twelve arrays were i mplanted for 6 months to determine structural and material biocompatib ility. Edema and hemorrhage were present around the short-term implant s, but involved less than 6% of the total area of the tissue covered b y the array. With chronic implants, leukocytes were rarely present and macrophages were found around roughly one-third of the tracks. Remnan ts of foreign material from the electrodes could be identified in less than 10% of the tracks. Gliosis was found around all tracks, forming an annulus between 20 and 40 mum thick. A capsule was not always prese nt, and never exceeded a thickness of 9 mum. These results suggest tha t the implantation procedure produces limited amounts of tissue damage , and that the arrays are biocompatible. However, the arrays insulated with polyimide over a primer had significantly greater involvement of macrophages, gliosis, and capsule formation than uncoated arrays and arrays insulated with polyimide without printer, perhaps indicating a reaction to aluminum oxide in the primer. (C) 1993 John Wiley & Sons, Inc.