Facile preparation of nanostructured octacalcium phosphate coatings on micro-arc oxidized magnesium with different functionalities for bone repair application.

Magnesium (Mg) has been considered as the next-generation orthopedic implant material due to its biodegradability, but high degradation rate and severe cytotoxicity hinder its clinical application. Preparing micro-arc oxidation (MAO)/octacalcium phosphate (OCP) composite coating is considered as an ideal approach to solve the problems. In this work, nanostructured OCP coatings with variable structures were prepared facilely on MAO coated Mg by chemical deposition (CD) in a simple trace PO ion contained Ca(NO) solution. The results show that nanostructured OCP grows and covers the MAO coating completely after CD. The morphology and thickness of OCP coating can be regulated by varying deposition time. The thinnest OCP coating with a fine structure is observed after 0.5 h of deposition, which shows the best cytocompatibility. Extending deposition time roughens the surface structure and thickens the coatings. The thickest OCP coating with a coarse structure can be obtained after 2 h of deposition, which shows the best corrosion resistance and mineralization. These results clearly indicate the functionality of the OCP coating can be easily tailored only by varying deposition time to meet different clinical requirements.