The Use of Genipin as an Effective, Biocompatible, Anti-Inflammatory Cross-Linking Method for Nerve Guidance Conduits

Abstract

A number of natural polymer biomaterial-based nerve guidance conduits (NGCs) are developed to facilitate repair of peripheral nerve injuries. Cross-linking ensures mechanical integrity and desired degradation properties of the NGCs; however, common methods such as formaldehyde are associated with cellular toxicity. Hence, there is an unmet clinical need for alternative nontoxic cross-linking agents. In this study, collagen-based NGCs with a collagen/chondroitin sulfate luminal filler are used to study the effect of cross-linking on mechanical and structural properties, degradation, biocompatibility, and immunological response. A simplified manufacturing method of genipin cross-linking is developed, by incorporating genipin into solution prior to freeze-drying the NGCs. This leads to successful cross-linking as demonstrated by higher cross-linking degree and similar tensile strength of genipin cross-linked conduits compared to formaldehyde cross-linked conduits. Genipin cross-linking also preserves NGC macro and microstructure as observed through scanning electron microscopy and spectral analysis. Most importantly, in vitro cell studies show that genipin, unlike the formaldehyde cross-linked conduits, supports the viability of Schwann cells. Moreover, genipin cross-linked conduits direct macrophages away from a pro-inflammatory and toward a pro-repair state. Overall, genipin is demonstrated to be an effective, safe, biocompatible, and anti-inflammatory alternative to formaldehyde for cross-linking clinical grade NGCs.

Keywords: cross-linking; formaldehyde; genipin; nerve guidance conduit; peripheral nerve injury.