Lithium-Incorporated Nanoporous Coating Formed by Micro Arc Oxidation (MAO) on Magnesium Alloy with Improved Corrosion Resistance, Angiogenesis and Osseointegration

Magnesium is an attractive candidate for orthopedic implants due to its similar mechanical properties to human bone and biodegradability. However, the high corrosion rate of magnesium accompanying with high pH value and poor osteogenic activity hinder its further application. In this study, we employed micro arc oxidation (MAO) to improve corrosion resistance by introduce nanoporous coating on AZ91 magnesium. Meanwhile, we added lithium, an angiogenic and osteogenic element, to the coating (named as Li-MAO) by reaction in a lithium-containing electrolyte to simultaneously enhance angiogenic and osteogenic activity of AZ91. The favorable corrosion resistance of Li-MAO was verified by electrochemical and immersion test in vitro. Better biocompatibility was observed in Li-MAO samples by cell counting kit-8 (CCK-8) and live/dead assay. The in vitro results of immunofluorescence staining, Alizarin red staining and osteogenic-related genes expression indicated better osteogenic ability of Li-MAO group, which may result from the activation the Wnt/β-catenin pathway. In vitro angiogenic tests also demonstrated better angiogenesis in Li-MAO group. A bone defect repair model was built to evaluate the in vivo osseointegration of samples. The outcomes of micro-computed tomography (Micro-CT) scanning, sequential fluorochrome labeling and Van Gieson staining suggested better in vivo bone repair ability of Li-MAO than other groups. Our promising results both in vitro and in vivo demonstrated that lithium-containing nanoporous coating can improve corrosion resistance, angiogenesis and osseointegration of magnesium alloy, which may forward the clinic application of Li-MAO magnesium.