Well-oriented magnesium hydroxide nanoplatelets coating with high corrosion resistance and osteogenesis on magnesium alloy

Magnesium alloys are nontoxic and promising as orthopedic metallic implants, but preparing a biocompatible Mg(OH)2 layer with high corrosion protection ability remains challenging. It is generally believed that the Mg(OH)2 layer, especially that formed in a natural condition, cannot provide desirable corrosion resistance in the community of corrosion and protection. Here, several Mg(OH)2 coatings were prepared by changing the pH values of sodium hydroxide solutions. These coatings were composed of innumerable nanoplatelets with different orientations and showed distinguished capability in corrosion resistance. The nanoplatelets were well-oriented with their ab-planes parallel to, instead of perpendicular to, the magnesium alloy surface by raising the pH value to 14.0. This specific orientation resulted in the optimal coating showing long-term corrosion protection in both in vitro and in vivo environments and good osteogenic capability. These finds manifest that the environment-friendly Mg(OH)2 coating can also provide comparable and better corrosion protection than many traditional chemical conversion films (such as phosphate, and fluoride).