A hydrothermal (HT) coating was applied to the biomedical Mg− Zn−Ca alloy surface by microarc oxidation (MAO) and heat treatment. Then, the corrosion resistance and biocompatibility of the coated alloy was evaluated in vitro and in vivo. The corrosion rate (CR) of HT-coated implants was significantly lower in experiment. In addition, this CR increased over time in vivo but was stable, albeit higher, in vitro. The proliferation, adhesion, and live activity of bone marrow stem cells (BMSCs) were significantly greater on the surface of the HTcoated Mg alloy in vitro. Serum Mg 2+ was always within the normal range in rabbits with implants, although Ca 2+ was higher than normal for both uncoated and coated scaffolds. There were no significant pathological effects on the main organs of alloy-implanted rabbits compared with healthy animals. Thus, the HT coating significantly improved the corrosion resistance and biocompatibility of the Mg−Zn−Ca alloy.

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BACKGROUND: Magnesium (Mg) alloy have biodegradation and mechanical properties that are similar to those of human bone, making it a promising candidate material for inclusion in implantable medical devices. OBJECTIVE: The osteointegration effect of Mg alloy scaffolds with different corrosion rates were studied and evaluated in large bone defect models. METHOD: Mg–Sr and Mg–Ca alloy scaffolds with a 20-μm Micro-arc oxidation (MAO) coating were used to repair critical bone defects for subsequent assessment of each alloy’s degradation and osteointegration by X-ray, Micro-CT, fluorescence and histological examination. RESULTS: At 12 weeks post-implantation, each defect was found to be effectively reconstructed by either of the Mg alloys based on X-ray and Micro-CT images. The corrosion rate (CR) of each Mg alloy – as calculated based on micro-computed tomography information – demonstrated that the MAO coating could provide effective protection for only 4 weeks post-surgery. From weeks 8 to 12, the CR of the Mg–Ca alloy scaffold increased from 1.34 ± 0.23 mm/y to 1.57 ± 0.16 mm/y. In contrast, the CR of the Mg–Sr alloy scaffold decreased from 0.58 ± 0.14 mm/y to 0.54 ± 0.16 mm/y. However, fluorescence and histological examination revealed more mature, closely and regularly arranged newborn osteocytes at the Mg–Ca scaffold-fracture interface e from weeks 8 to 12 after surgery. RESULTS: The Mg–Sr scaffold was more corrosion resistant and the Mg–Ca scaffold yielded a better overall repair, which indicates that the CR of magnesium alloys matches the rate of new bone formation and is the key to repair bone defects as a bone substitute.