Degradation behavior and osteogenic activity of octacalcium phosphate modified MgO coatings on magnesium

Abstract

To further enhance the corrosion resistance and osteogenic activity of the porous micro-arc oxidation (MAO) derived MgO ceramic coating on biomedical magnesium (Mg), octacalcium phosphate (OCP) layers with different microstucture were prepared on MAO coating by chemical deposition (CD) method to fabricate MAO/CD composite coatings. The in vitro degradation behaviors of MAO/CD-coated samples were evaluated by immersion in simulated body fluid (SBF) and electrochemical impedance spectroscopy (EIS) measurement. Their effects on in vitro MC3T3-E1 cell differentiation were investigated by examining alkaline phosphatase (ALP) activity and expression of main osteogenic-related genes. The in vitro immersion tests show that MAO/CD coatings rarely experience destruction and only micro-cracks occur after 96 h. EIS tests indicate that MAO/CD coatings slow down the degradation rate of Mg observably. In addition, MAO/CD coatings improve osteogenic differentiation of MC3T3-E1 cells compared to MAO coating, which is ascribed the lightened alkalization of the surrounding medium as well as up-regulated intracellular Ca2+. MAO/CD coating deposited in 2 h endows Mg the slowest degradation rate and excellent osteogenic differentiation induction activity.