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

Abstract In this study, bone-like apatite formation on manganese-hydroxyapatite (Mn-HA) coatings formed on Ti-6Al-4V by plasma electrolytic oxidation (PEO) has been investigated by several techniques. Ti-6Al-4V ELI disks were used as substrates for PEO treatment. Test specimens were used as anodes, and a Pt rod was used as the cathode in an electrolytic solution containing Mn. The applied voltage was 280 V, and the deposition time was 3 min. To examine the bioactivity, the PEO films formed on Ti-6Al-4V were immersed in SBF for 12 h. The PEO films and the Ti-6Al-4V surface after immersion in SBF were characterized by a thin-film X-ray diffractometer, field-emission scanning electron microscopy, and energy dispersive X-ray spectroscopy. 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.