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Hydroxyapatite-Titania nanotube composite as a coating layer on Co-Cr-based implants: Mechanical and electrochemical optimization

Abstract:

Inadequate mechanical properties of pure hydroxyapatite (HA) coating layers make it an unsuitable candidate for many load-bearing orthopedic implants. In this study, Titania nanotubes (TNT) and HA were synthesized using Rapid Breakdown Adonization (RBA) and sol-gel methods, respectively. The sintering process at different temperatures was then conducted for the phase transformation of titanium. HA-TNT mixtures in different quantities and phases were prepared for coating on Co-Cr-based substrates. To optimize the coated HA-TNT composite layer in term of hardness, bonding strength and corrosion potential, empirical models based on Response Surface Methodology (RSM) were developed. The synthesized TNT and HA-TNT coated samples were characterized using X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Transmission Electron Microscopy (TEM). The pbkp_redicted models generated by RSM were compared with the experimental results, and close agreement was observed. While the models demonstrate that TNT quantity is a more significant factor than sintering temperature in improving hardness (H), bonding strength (P) and the corrosion potential (Ecorr) of a coated substrate, sintering temperature still has a considerable effect on H and Ecorr. The optimum HA-TNT composite coating layer in terms of the mechanical and electrochemical properties were obtained with a TNT ratio of 1.07 (wt%) at a sintering temperature of 669.11 °C.