Preparation and bioactivity of micro-arc oxidized calcium phosphate coatings

Calcium phosphate (CaP) coatings were prepared on ZK60 magnesium alloy by micro-arc oxidation (MAO) in electrolyte containing calcium acetate monohydrate (CH3COO)2Ca·H2O) and disodium hydrogen phosphate dodecahydrate (Na2HPO4·12H2O). Scanning electron microscope (SEM), energy-dispersive X-ray spectrometry (EDX) and X-ray diffractometer (XRD) were employed to characterize the microstructure, elemental distribution and phase composition of the CaP coatings respectively. Simulated body fluid (SBF) immersion test was used to evaluate the coating degradability and bioactivity. After 30 days of SBF immersion, the CaP coatings effectively reduce the degradation rate. The surfaces of CaP coatings are covered by a new layer formed of numerous needle-like, spherical and columned calcium phosphates. SEM, EDX and XRD results suggest that these calcium phosphates are bioactive calcium phosphate phases such as hydroxyapatite (Ca10(PO4)6(OH)2, HA) and calcium pyrophosphates (Ca2P2O7, CPP). The formation of these calcium phosphates indicates that the CaP coatings have bioactivity.