Investigation of hydroxyapatite (HAP) containing coating on grade 2 titanium alloy prepared by plasma electrolytic oxidation (PEO) at low voltage

In this work, plasma electrolytic oxidation (PEO) process was used to produce bioactive coatings, mainly composed by hydroxyapatite (Hap) and titanium oxide, on grade 2 titanium alloy. All PEO treatments were carried out using a maximum voltage of 315 V, a lower value in comparison with the works present in literature, thus resulting a more environmentally friendly process. The effects on the PEO coatings of KOH addition to electrolyte and of working in direct or pulsed current mode, were also investigated. The morphology and elemental composition of the coatings were characterised by scanning electron microscopy (SEM), whereas the phase analysis was carried out with X-ray diffraction (XRD). The corrosion resistance properties were investigated by open circuit potential measuraments, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. Moreover, cell-adhesion biological tests were performed. SEM analysis evidenced the presence of needle-shape crystals of hydroxyapatite, as confirmed by XRD, that totally or partially filled the pores of PEO layer. The corrosion test showed an improvement in the corrosion behaviour of the PEO coated samples in comparison with the untreated sample. Cell-Adhesion biological tests evidenced excellent cytocompatibility of the coatings with human cells and an improvement in the cell adhesion in comparison with the untreated sample.