Effect of Ca/P ratio on the structural and corrosion properties of biomimetic Ca P coatings on ZK60 magnesium alloy

Magnesium and its alloys have attracted much attention as metallic biodegradable implants for their excellent biocompatibility and mechanical properties. However, magnesium has a poor corrosion resistance, causing its rapid degrading in vivo via an electrochemical reaction, which has become a major obstacle to their applications in implants. In this work, Ca--P coating was successfully coated on the ZK60 magnesium alloys by a simple hydrothermal deposition method. The mechanisms of the hydrothermal reactions of Ca--P coatings on Mg substrate are described in details. The effect of Ca/P ratio in the hydrothermal solution on the phase composition, microstructure and biodegradation properties of Ca--P coatings on ZK60 alloys was investigated by varying the Ca/P ratio from 0.83 to 4.18. The morphology of the Ca--P coating changed significantly with the Ca/P ratio. Biodegradation behavior of the Ca--P coating magnesium was characterized by anodic polarization and immersion tests in a simulated body fluid. It is revealed that the corrosion resistance of ZK60 magnesium alloy was greatly improved with the biomimetic Ca--P coatings, and the ZK60 alloy with Ca--P coating deposited at Ca/P ratio of 1.67 has the best corrosion resistance, which indicates that the Ca--P coatings are promising for improving the biodegradation properties of Mg-based orthopedic implants and devices.