Development and Biocompatibility evaluation of silk fibroin-based nerve grafts for peripheral nerve regeneration

Silk fibroin (SF) have been used in the field of bone or ligament tissue engineering. We developed a novel biomimetic design of the SF-based nerve graft (SF graft) which was composed of a SF-nerve guidance conduit (NGC). The SFNGC prepared via well-established procedures exhibits an eggshell-like microstructure that is responsible for its superior mechanical and permeable properties beneficial to nerve regeneration. The inner wall displays a 100-µm-thick netted structure formed by SF fibers of 10 µm diameter, which were spread out as a stiffener. The data also indicate that the cumulative release of vitamin B12 is almost 100% after 75 min of release. MTT assay was performed to determine the in vitro cytotoxicity of the SF-NGC extract fluid on the cultured L929 cells derived from an immortalized mouse fibroblast cell line. The adult rat was subjected to implantation of the SF graft for bridging a 10-mm long sciatic nerve defect. Then the following- up experiments at initial stage (1–4 weeks) of nerve regeneration including routine blood tests and histochemical investigation were used to evaluate the in vivo biocompatibility of the SF graft with peripheral nerve. The results suggested the noncytotoxicity of the SF-NGC with grade 0 as per the U.S. Pharmacopeia guidelines. The outcome of peripheral nerve repair at six months post-implantation was evaluated by a combination of electrophysiological assessment, Fluoro Gold retrograde tracing and histological investigation. The examined functional and morphological parameters show that SF grafts could promote peripheral nerve regeneration. Collectively, these data indicate that SF graft raised a potential possibility of using these newly developed nerve grafts as a promising alternative to nerve autografts.