Influence of hydrothermal treatment on the surface characteristics and electrochemical behavior of Ti-6Al-4V bio-functionalized through plasma electrolytic oxidation

The performance of biomaterials in general and orthopaedic biomaterials in particular is dependent on both the chemistry and topography of their surfaces. It is therefore important to tailor both of those aspects through an appropriate surface modification technique. Here, we examined the influence of hydrothermal treatment on the surface characteristics and electrochemical behavior of Ti-6Al-4V specimens whose surfaces were modified using plasma electrolytic oxidation (PEO). Even though no calcium-phosphorous related crystalline compound was identified in the XRD spectra of PEO layers, hydroxyapatite crystals were clearly detectable after the applied hydrothermal treatment. The partial water absorption of the HA crystals and their needle-like morphology resulted in a significant increase in the wettability of the surfaces. However, the application of post-PEO hydrothermal treatment also decreased the corrosion resistance of the PEO layers. The numerical results of electrochemical impedance spectroscopy demonstrated that the optimized surface properties and corrosion resistance were achieved in one of the groups, namely PEO-HT3, where the HA nanocrystals homogenously covered the entire surface of the specimens.