Plasma electrolytic oxidation deposited HAp-Ta2O5 composite coatings on Ti6Al4V for biomedical applications: The importance of Ta2O5 reinforcing phase

In this research, the focus was placed on enhancing the properties of hydroxyapatite (HAp) coating by the addition of various concentrations of tantalum pentoxide (Ta 2 O 5 ) nanoparticles, ranging from 0 to 1.5 g/L, to its electrolyte solution. The HAp-Ta 2 O 5 composite coatings were deposited on the Ti6Al4V metallic implant using the plasma electrolytic oxidation technique. The results of the X-ray diffraction test indicated that the increased concentration of Ta 2 O 5 nanoparticles has no significant effect on the phase composition of the coatings. The denser and rougher coatings were fabricated when 1.5 g/L of Ta 2 O 5 nanoparticles were added to the solution. The favorable microstructural properties of the HAp-1.5 g/L Ta 2 O 5 composite coating resulted in a notable improvement in the mechanical properties, i.e., >40% increase in both microhardness and bonding strength compared to HAp. The corrosion resistance of the coated implants was evaluated through electrochemical impedance spectroscopy and potentiodynamic polarization tests. The inclusion of Ta 2 O 5 nanoparticles in HAp coating led to a 72% reduction in the corrosion current density of HAp, indicating the constructive contribution of the nanoparticles to improved corrosion protection. The samples were incubated in simulated body fluid for 7 days to assess their in vitro immersion performance. All of the PEO-derived coatings stimulated the nucleation and growth of apatite grains, showing their superior biomineralization ability. An obvious decrease in the level of harmful ions such as Al 3+ and V 5+ released from the surface of composite coatings was obtained. These findings suggest that the developed system has potential for dental and orthopedic applications.