Calcium phosphate coatings enhance biocompatibility and degradation resistance of magnesium alloy: Correlating in vitroand in vivostudies

Magnesium (Mg) and its alloys are promising biodegradable materials for orthopedic applications. However, one of the major problems is their rapid degradation rate with quick evolution of hydrogen gas. To overcome this problem, calcium phosphate (CaP) coatings have been used to improve the degradation resistance and the biocompatibility of Mg materials. This study focuses on the comparison and correlation of the in vitroand in vivodegradation and biocompatibility behaviors of these materials. A CaP coating consisting of dicalcium phosphate dihydrate (DCPD) was deposited on an AZ60 Mg alloy by the chemical conversion method. Then, the in vitrodegradation testing including electrochemical and immersion tests, and in vivoimplantation of the CaP coated Mg alloy were conducted to compare the degradation behaviors. Next, the in vitrocell behavior and in vivobone tissue response were also compared on both uncoated and CaP-coated Mg samples. Data showed that the CaP coating provided the Mg alloy with significantly better biodegradation behavior and biocompatibility. The in vitroand in vivobiocompatibility tests exhibited good consistency while not the case for biodegradation. Results showed that the in vitroelectrochemical test could be a quick screening tool for the biodegradation rate, while the in vitroimmersion degradation rate was often 2–4 folds faster than the in vivodegradation rate.