Characterization and property of dual-functional Zn-incorporated TiO2 micro-arc oxidation coatings: The influence of current density

Abstract In the present work, with the addition of ZnO nanoparticles (NPs) as Zn source, the Zn-incorporated TiO2 coatings were successfully produced by the facile one-step micro-arc oxidation (MAO) method. The influence of current density on the microstructural features and biological properties of Zn-incorporated TiO2 MAO coatings were systematically examined. It is revealed that, at a relatively low current density of 0.1 A/cm2, Zn species either locate on the coating surface as ZnO nano-sheet clusters or entrap within the coating. By contrast, Zn species tend to fuse into the coating at a relatively high current density of 0.5 A/cm2, which exhibits a three-layered structure with significant difference of crystallinity, composition and morphology between different layers. The biological experiments indicate that different current densities result in different osteogenic activities and antibacterial properties of Zn-incorporated TiO2 coatings. The presence of a Zn-depleted amorphous outer-layer on the MAO coating produced at the current density of 0.5 A/cm2 favours the deposition of apatite-like phases, but retards the release of Zn ions, which thus results in its higher osteogenic activity with lower antibacterial capability compared to that produced at the current density of 0.1 A/cm2. In summary, dual-functional Zn-incorporated TiO2 coatings could be successfully produced through the facile one-step MAO method, with both antibacterial property and bone formability significantly affected by the current density of MAO process.