Fabrication of GDNF-Gel/HA-Mg nerve conduit and its role in repairing peripheral nerve defects

BACKGROUND: Magnesium (Mg) and its alloys are receiving increasing attention in peripheral nerve regeneration, but they were limited due to the low corrosion resistance and rapid degradation. In this study, GDNF-Gel/HA-Mg was prepared and its value in peripheral nerve defects repairment was explored both in vitro and in vivo. METHODS: A hydroxyapatite (HA) coating was first applied to the pure Mg surface, followed by the formation of gelatin methacrylate (GelMA) loaded with glial cell-derived neurotrophic factor (GDNF) on the HA-coated Mg surface. GDNF-Gel/HA-Mg corrosion resistance was explored. The effect of GDNF-Gel/HA-Mg conduit on Schwann cell proliferation and migration abilities were investigated. And sciatic nerve defects models were established to explored the role of GDNF-Gel/HA-Mg conduit in peripheral nerve defects repairment. FINDINGS: The electrochemical, immersion, and hydrogen evolution experiments indicated that the corrosion resistance in phosphate buffer saline (PBS) of pure Mg was significantly improved by the GDNF-Gel/HA coating. Cell cycle, Cell Count Kit-8 (CCK-8), and clone formation assays indicated that GDNF-Gel/HA-Mg promoted the proliferation of Schwann cells. Scratch and Transwell assay results demonstrated that GDNF-Gel/HA-Mg promoted Schwann cell migration ability dose-dependently. GDNF-Gel/HA-Mg was found to enhance the secretion of nerve growth factor (NGF) and the expression of p75(NTR). Flow cytometry results showed that GDNF-Gel/HA-Mg could reduce H(2)O(2)-induced oxidative stress and Schwann cell apoptosis. GDNF-Gel/HA-Mg inhibited M1 macrophage polarization while facilitated M2 macrophage polarization in a concentration-dependent manner. The in vivo studies demonstrated that GDNF-Gel/HA-Mg conduit could significantly promote the regeneration and myelination of sciatic nerve, as well as the recovery of denervated gastrocnemius atrophy. INTERPRETATION: The GDNF-Gel/HA-Mg conduit prepared in this study exhibited good hydrophilicity and corrosion resistance and greatly enhanced the proliferation, migration, and invasion abilities of Schwann cells, as well as peripheral nerve regeneration.