gms | German Medical Science

Objectives/Interrogation: The nerve guidance conduit can connect two nerve ends, guide axonal regeneration and offer a neurotrophic environment to Schwann cell aggregation and proliferation. Two major factors are involved in fabricating an excellent nerve conduit, material selection and surface modification. As a conductive nanomaterial, graphene has huge potentials in nerve function restoration by promoting electrical signal transduction and metabolic activities with unique topological properties. Polydopamine (PDA) and arginylglycylaspartic acid (RGD) are peptides that can improve cell adhesion in tissue engineering. We intend to evaluate the surface-modified graphene nanoscaffold in the restoration of severe peripheral nerve defects.

Methods: We evaluated single-layered graphene (SG) and multi-layered graphene (MG) in the peripheral nerve repair. We used polycaprolactone (PCL) as the substrate scaffold and fabricated the PDA/RGD-SG/PCL and PDA/RGD-MG/PCL nanoscaffold using layer by layer casting (LBLC) method. We examined the surface morphology and conductive capacity. We performed in vitro assays to evaluate Schwann cell (SC) proliferation, adhesion, neural expression on different nanoscaffolds. For in vivo studies, we created a 15-mm sciatic nerve defect model in Sprague Dawley (SD) rats. We evaluated their functional, electrophysiological, morphological performances at 6, 12 and 18 weeks after injury.

Results and Conclusions: The inner-most and outer-most layers of RGD and PDA were beneficial to cell adhesion and proliferation. The graphene/PCL double layers intensified the tubular structure and allowed certain stiffness in vivo. Our multi-layered macroporous nerve conduit allowed exchanges of nutrients and oxygen via excellent permeability, strong mechanical support, appropriate biodegradation rate, and flexibility for complete nerve regrowth. The glial fibrillary acidic protein (GFAP), beta tubulin (Tuj1) and S100 expression of Schwann cells was enhanced by graphene nanoscaffold, indicating the beneficial effects in improving neural activity. The number of myelinated axons, thickness of myelin sheath, regenerated axon area and average myelinated axon diameter of the regenerated nerves from graphene conduit were significantly higher than pure PCL conduit group. Nerve conducting velocity, distal compound motor action potential and sciatic function index were also better in the graphene conduit group. In addition, PDA/RGD-SG/PCL and PDA/RGD-MG/PCL conduits also promoted myelin sheath and axonal regeneration.