Biocompatibility evaluation of parylene C and polyimide as substrates for peripheral nerve interfaces

For assessing the suitability of a given material for peripheral nerve implantation, acute and chronic tests to investigate tissue reaction, and evaluate the thickness of fibroblast layers that surround the material and the presence of inflammatory cells are mandatory. In this study we compared in vivo the biocompatibility of parylene C and polyimide, two materials intended for fabrication of neural electrodes. We have tested these two materials after implantation of thin devices in the peripheral nerve of rats, by functional and morphological methods, assessing thickness of the fibrotic capsule, signs of inflammation and axon survival in areas close to the implant. Intraneural implantation of parylene C and polyimide devices did not produce any functional alteration in the sciatic nerve, as evidenced by electrophysiological, locomotion and nociceptive functional tests. The intraneural devices were encapsulated within a fibroblastic tissue. Resolution of the inflammatory infiltrate took 4-8 weeks. In conclusion, both parylene and polyimide electrodes show biocompatible characteristics and induce a similar fibrotic reaction after chronic intraneural implantation.