Enhanced Antibacterial Performance of Functionally Graded Biomaterial ‎Coatings on Ti-6Al-4V Alloy‎

Abstract

The electrophoretic deposition (EPD) technique was used to prepare seven-layered functionally graded hydroxyapatite/titanium dioxide (HAp/TiO₂) coatings on Ti–6Al–4V alloy for biomedical implant applications. The coating structure was designed with a compositional gradient from pure TiO₂ near the substrate to pure HAp on the outer surface, so as to combine the corrosion resistance of TiO₂ with the bioactivity of HAp. The coated samples were heat-treated at 950°C for one hour under an argon atmosphere to improve the coating stability and phase formation after deposition.

The structural characteristics of the coatings were evaluated by X-ray diffraction (XRD). The obtained results confirmed the presence of hydroxyapatite as well as anatase and rutile phases of titanium dioxide. Furthermore, other calcium phosphate phases were observed due to the partial decomposition of hydroxyapatite during the sintering process. The corrosion behavior was evaluated by potentiodynamic polarization tests in Ringer’s solution, where the coated samples showed better corrosion resistance than the uncoated Ti–6Al–4V alloy. with corrosion characteristics gradually increasing from S1 to S7. S7 coating showed the highest noble corrosion potential (Ecorr = −0.23 V), lowest corrosion current density (Icorr = 2.02 µA/cm2) and lowest corrosion rate (CR = 0.018 mpy). The antibacterial activity against *Escherichia coli* was also evaluated by the inhibition zone method. The produced coatings showed good antibacterial activity and reduced the development of E. coli bacteria. The results indicate that functionally graded HAp/TiO2 coatings can greatly improve the surface properties of Ti-6Al-4V alloy  concurrently boosting corrosion resistance and antibacterial performance and have great potential in biomedical implant applications.