A facile chemical conversion approach for constructing a Sr-doped scholzite coating on micro-arc oxidized magnesium alloy with optimized corrosion and biocompatibility

Inspired by the inorganic composition of bone, this study fabricated a Sr-doped scholzite biomimetic coating on the surface of ZMJ310 alloy after micro-arc oxidation (MAO). By comprehensively considering the solution pH, temperature, and processing time, the optimal parameters for preparing the composite coating were determined as pH 5.3, 95°C and 3.5 h. The formation of the Sr-doped scholzite coating begins with the dissolution of the MAO layer, which supplies OH - and metal cations for the development of the composite coating. Due to the similar ionic radii of Ca 2+ and Sr 2+ and their comparable binding capacities with PO 4 3- , Sr 2+ is incorporated into the coating in a doped form. During the corrosion process, since the bonding between the conversion coating and the MAO layer is a combination of mechanical and chemical interlocking, the simulated body fluid can still reach the MAO layer, eventually leading to coating detachment. Nevertheless, corrosion resistance evaluations revealed that the alloy prepared under optimal conditions exhibited a low long-term hydrogen evolution rate of 0.136 mm/y, demonstrating excellent corrosion performance. The formation of the composite coating effectively regulated the ion release kinetics of the alloy, resulting in favorable capabilities for promoting cell proliferation, differentiation, and osteogenic induction.