Incorporation of Mg-phenolic networks as a protective coating for magnesium alloy to enhance corrosion resistance and osteogenesis in vivo

Magnesium (Mg) and its alloys have been intensively studied to develop the next generation of bone implants recently, but their clinical application is restricted by rapid degradation and unsatisfied osteogenic effect in vivo. A bioactive chemical conversion Mg-phenolic networks complex coating (eEGCG) was stepwise incorporated by epigallocatechin-3-gallate (EGCG) and exogenous Mg²⁺ on Mg-2Zn magnesium alloy. Simplex EGCG induced chemical conversion coating (cEGCG) was set as compare group. The in vitro corrosion behavior of Mg-2Zn alloy, cEGCG and eEGCG was evaluated in SBF using electrochemical (PDP, EIS) and immersion test. The cytocompatibility was investigated with rat bone marrow mesenchymal stem cells (rBMSCs). Furthermore, the in vivo tests using a rabbit model involved micro computed tomography (Micro-CT) analysis, histological observation, and interface analysis. The results showed that the eEGCG is Mg-phenolic multilayer coating incorporated Mg-phenolic networks, which is rougher, more compact and much thicker than cEGCG. The eEGCG highly improved the corrosion resistance of Mg-2Zn alloy, combined with its lower average hemolytic ratios, continuous high scavenging effect ability and relatively moderate contact angle features, resulting in a stable and suitable biological environment, obviously promoted rBMSCs adhesion and proliferation. More importantly, Micro-CT, histological and interface elements distribution evaluations all revealed that the eEGCG effectively inhibited degradation and enhanced bone tissue formation of Mg alloy implants. This study puts forward a promising bioactive chemical conversion coating with Mg-phenolic networks for the application of biodegradable orthopedic implants.