Yao, Li

Microsurgical techniques for the treatment of large peripheral nerve injuries (such as the gold standard autograft) and its main clinically approved alternative—hollow nerve guidance conduits (NGCs)—have a number of limitations that need to be addressed. NGCs, in particular, are limited to treating a relatively short nerve gap (4 cm in length) and are often associated with poor functional recovery. Recent advances in biomaterials and tissue engineering approaches are seeking to overcome the limitations associated with these treatment methods. This review critically discusses the advances in biomaterial-based NGCs, their limitations and where future improvements may be required. Recent developments include the incorporation of topographical guidance features and/or intraluminal structures, which attempt to guide Schwann cell (SC) migration and axonal regrowth towards their distal targets. The use of such strategies requires consideration of the size and distribution of these topographical features, as well as a suitable surface for cell–material interactions. Likewise, cellular and molecular-based therapies are being considered for the creation of a more conductive nerve microenvironment. For example, hurdles associated with the short half-lives and low stability of molecular therapies are being surmounted through the use of controlled delivery systems. Similarly, cells (SCs, stem cells and genetically modified cells) are being delivered with biomaterial matrices in attempts to control their dispersion and to facilitate their incorporation within the host regeneration process. Despite recent advances in peripheral nerve repair, there are a number of key factors that need to be considered in order for these new technologies to reach the clinic.

In the absence of donor tissues, conduits are needed for axons to regenerate across nerve defects, yet single-channel conduits may result in axonal dispersion, and multichannel synthetic polymer conduits have failed due to dimensional instability. The goal of this study was to create a robust collagen-based nerve conduit with multiple submillimeter-diameter channels to facilitate nerve guidance. Toward this goal, we have developed a novel multistep molding technique to create single-, four-, and seven-channel conduits from collagen and examined the effects of crosslinking with 0–60 mM (1-ethyl-3-(3-dimethylaminopropyl) carbodiimide [EDC] in N -hydroxysuccinimide) on geometric, enzymatic, and thermal stability, mechanical properties, and cellular behavior. Multichannel collagen conduits crosslinked with 30 mM EDC and 10 mM N -hydroxysuccinimide demonstrated low degradation rate (∼10% at 2 days), high shrinkage temperature (>75°C), and constant channel morphology out to 30 days in saline. Neurite outgrowth remained unaffected from cultured dorsal root ganglia explants seeded on collagen scaffolds with up to 30 mM EDC crosslinking. Compared with single-channel conduits, multichannel collagen conduits showed superior structural compressive, tensile, and bending stiffness. Taken together, these results suggest that the crosslinked multichannel collagen conduits possess favorable material and mechanical properties for nerve regeneration applications.