Silicon carbide neural implants: In vivo neural tissue reaction

Novel materials are needed for intracortical neural implants (INI) to extend their reliability and functionality beyond a few years. Cubic silicon carbide (3C-SiC) is a chemically inert, physically robust semiconductor that has shown, through extensive in vitro testing, a high biocompatibility with neural cells. Recently we have shown that 3C-SiC does not attract a negative immune response from microglia in vivo, but the implants size did not allow adequate investigation of tissue response [1]. We produced a passive implant to test the in vivo tissue reaction of C57BL/6J mice to 3C-SiC and compare to our positive control of silicon (Si). Dual, triangular shanks were fabricated from each material and combined into a single device which was then implanted simultaneously into three C57BL/6J mouse brains for 35 days. The mice were perfused with 4% paraformaldehyde and the brains treated using immunohistochemistry. Fluorescence microscopy indicated that Si produced the expected increased inflammatory response from both microglia/ macrophage and astrocyte cells, whereas 3C-SiC shows minimal inflammatory reaction from these glial cells. Si also created tissue voids larger than the implants themselves whereas 3C-SiC showed minimal voids and even still had neuronal processes in contact with the implant. Our conclusion is that 3C-SiC shows great potential for use within the neural environment and should be fashioned into active INI to evaluate signal quality over time.