Tissue response to potential neuroprosthetic materials implanted subdurally.

A histologic study was made of the response of the leptomeninges and underlying cerebral cortex of the cat to subdural implantation of 3 insulating materials (HR605-P, Parylene-C and PI-2555) and a polymeric electrode component (MMA/MAPTAC) for periods of 8 and 16 wk. The tissue reactions were compared with those elicited by the arrays of Dacron mesh matrices, pure platinum controls and by positive controls (Ag-AgCl) known to cause reactions in the brain. Sites beneath the Dacron mesh matrix, pure platinum control implants and beneath all insulating materials implanted for 8 and 16 wk appeared indistinguishable, exhibiting little tissue reaction. All neurons appeared normal. The leptomeninges and cortex beneath the Ag-AgCl implants showed a chronic inflammatory reaction after 8 and 16 wk. Despite varying amounts of oedema, gliosis and ingrowth of connective tissue in the molecular layer, virtually all underlying neurons appeared normal.