Bone-like apatite formation on manganese-hydroxyapatite coating formed on Ti-6Al-4V alloy by plasma electrolytic oxidation

The PEO surface presented large and irregular pores, and the number of pores increased as the Mn content increased. For the PEO-treated samples, anatase peaks were detected by X-ray diffraction, and the HA peak intensity increased as the Mn content increased. The Ca/P ratio decreased, whereas the (Ca + Mn)/P ratio increased, as the Mn content increased. The coatings without Mn on the micropores had a small granular shape, and the pores were covered with HA after the immersion in SBF. As the Mn concentration increased, all Mn-HA coating surfaces became more dense, and microcracks appeared on the coating surface.