Calcium phosphate coatings enhance biocompatibility and degradation resistance of magnesium alloy: Correlating <i>in vitro</i> and <i>in vivo</i> studies.

Abstract

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 <i>in vitro</i> and <i>in vivo</i> degradation 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 <i>in vitro</i> degradation testing including electrochemical and immersion tests, and <i>in vivo</i> implantation of the CaP coated Mg alloy were conducted to compare the degradation behaviors. Next, the <i>in vitro</i> cell behavior and <i>in vivo</i> bone 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 <i>in vitro</i> and <i>in vivo</i> biocompatibility tests exhibited good consistency while not the case for biodegradation. Results showed that the <i>in vitro</i> electrochemical test could be a quick screening tool for the biodegradation rate, while the <i>in vitro</i> immersion degradation rate was often 2-4 folds faster than the <i>in vivo</i> degradation rate.