Improved viability of chronic neural implants using thin microelectrodes

The recording interface between neurons and an implanted microelectrode recording site is often compromised due to gliosis, rendering the implant nonfunctional under chronic conditions. The objective of this project is to design novel microelectrodes that will minimize gliosis under chronic implantation. We test the hypothesis that gliosis can be minimized or eliminated by reducing the cross-sectional area of the chronic implant. Current microelectrodes for recording chronic action potentials range from 25 μm to 100 μm or more in diameter. We fabricated neural implants by coating 12 μm stainless steel microwires with polyglycolic acid (PGA), a biodegradable polymer, resulting in a final diameter of 25 μm. Twelve rats were implanted with the PGA coated electrode on the left hemisphere in the somatosensory cortex and with the regular 25 μm stainless microelectrode in the right hemisphere. The rat brains were perfused at 4 weeks after implantation and stained for glial fibrilliary acidic protein (GFAP) and microtubule associated protein-2 (MAP-2). The microelectrodes coated with PGA produced minimal gliosis compared to the conventional 25 μm wire and other silicon based microelectrodes. We conclude that ultra-thin neural implants with minimum cross-sectional area coated with PGA will greatly improve the functionality of microelectrodes under chronic conditions.