Corrosion resistance and surface biocompatibility of a microarc oxidation coating on a Mg–Ca alloy

The Mg–Ca alloy system has been proposed as a potential new kind of degradable biomaterial with possible application within bone. Here microarc oxidation (MAO) coatings were fabricated on top of a Mg–Ca alloy using different applied voltages and the effect of applied voltage on the surface morphology and phase constitution, hydrogen evolution, pH variation in the immersion solution and in vitro biocompatibility of the MAO coating on the Mg–Ca alloy were extensively studied. It was found that the thickness and pore size of the MAO coating increased with the increasing applied voltage, whereas some micro-pores could be seen inside the 400 V treated MAO coating. The 360 V treated MAO coating gave the best long-term corrosion resistance during a 50 days immersion test. All the MAO coatings could promote MG63 cell adhesion, proliferation and differentiation in comparison with the uncoated Mg–Ca alloy sample, due to significantly reduced Mg ion release and pH value variations in the culture medium. After 5 days culture well-spread and elongated MG63 cells could be seen on the surface of the 360 V and 400 V MAO coatings, in contrast to no cells on the uncoated Mg–Ca alloy sample. In summary, MAO showed beneficial effects on the corrosion resistance of, and thus improved cell adhesion to, the Mg–Ca alloy, and should be a good surface modification method for other biomedical magnesium alloys.