Microwave aqueous synthesis of hydroxyapatite bilayer coating on magnesium alloy for orthopedic application

Abstract Magnesium and magnesium alloys as promising biodegradable implants gain increasing interest. To improve their corrosion resistance and cytocompatibility, hydroxyapatite (HA) coatings with double-layer structure were synthesized on magnesium alloy through a rapid microwave aqueous chemical route. The coating prepared with microwave heating time of 10 min consisted of cotton-like HA as the surface layer and strip-like HA as the bottom layer, and the coating thickness was ∼10.0 μm. The growth kinetic, electrochemical property, degradation, mineralization and cytocompatibility of HA coated and naked magnesium alloys were investigated. Potentiodynamic polarization test demonstrated that corrosion current density of HA coated magnesium alloy prepared with microwave heating time of 10 min was ∼100 times lower than that of the naked counterpart. Immersion test indicated that the strip-like HA layer with thickness of ∼7.7 μm and low solubility endowed magnesium alloy with initial-stage protection; the nano-scale cotton-like HA layer exhibited high HA mineralization capacity. The mineralized layer reached ∼12.7 μm in thickness after 24 days’ immersion, eventually integrated with the original HA bilayer coating, providing favorable long-term protection for magnesium alloy. Moreover, HA coated magnesium alloy prepared with microwave heating time of 10 min enhanced osteoblast proliferation than the naked counterpart. These attractive results indicated that this HA bilayer coating is a potential protective coating on biodegradable magnesium and magnesium alloys for orthopedic application.