In vitro degradation and mineralization of strontium-substituted hydroxyapatite coating on magnesium alloy synthesized via hydrothermal route

Abstract

Magnesium (Mg) and its alloy as promising biodegradable orthopaedic implants have gained immense attention by virtue of their superior biocompatibility and mechanical compatibility. In order to increase the long-term corrosion resistance of Mg and its alloys in clinical application, in this work, a series of strontium-substituted hydroxyapatite (SrHA) coatings were constructed on Mg alloy via hydrothermal route. These SrHA coatings possessed bilayer structure with flower-like clusters as the surface layer and flat surface as the bottom layer. Coating III with Sr/Ca molar ratio of 0.07 exhibited crack-free bottom layer and good interfacial adhesion, and its electrochemical corrosion resistance was higher than the counterparts. Moreover, this coating with high dissolution and rough surface rapidly induced SrHA mineralized layer formation, which gradually grew dense and thick, providing favorable long-term protection for Mg alloy. After immersion in simulated body fluid for 29 days, the average degradation rate of Mg alloy decreased to 0.17 mg/day·cm². The present work demonstrated that this SrHA coating was a potential protective coating for Mg and Mg alloy implants.