Application of hydroxyapatite-titanium dioxide composite coating on 316 steel and investigation of its antibacterial properties

• HAp/TiO₂ composite coatings were uniformly deposited on SS316 using electrophoretic deposition. • The composite coating exhibited lower surface roughness and improved surface homogeneity compared to pure HAp. • An optimized HAp/TiO₂ ratio (1:1) significantly enhanced antibacterial activity against Staphylococcus aureus. • Coexisting crystalline phases of hydroxyapatite and anatase TiO₂ were successfully preserved after coating. • The synergistic effect of HAp and TiO₂ improved antibacterial performance while maintaining bioactive surface properties In recent years, the use of biocompatible coatings to improve the surface properties of biological, medical, and implant metals has received widespread attention. In this study, composite coatings consisting of natural hydroxyapatite (extracted from bovine bone) and titania nanoparticles (TiO₂) in various ratios were synthesized and applied to the surface of 316 steel by electrophoretic deposition to enhance the antibacterial, surface, and structural properties. XRD results showed that hexagonal hydroxyapatite (HAp) and anatase TiO₂ phases were well present in the composite coatings. The presence of key functional groups, such as PO₄³⁻, OH, and Ti-O, was confirmed by FTIR analysis, which plays an important role in improving the biological and antibacterial properties. The HAp structure contains nanopores, and with increasing TiO₂ content, the coating became more uniform and denser. The results of profilometry and water drop contact angle tests showed a decrease in the average surface roughness and an increase in uniformity in the composite samples compared to pure HAp coatings. The antibacterial properties were evaluated against both Gram-positive and Gram-negative bacteria. The results showed that the optimal composition with a ratio of 1:1 (TiO 2 /HAp) had the highest reduction in bacterial growth. This favorable performance is attributed to the presence of active functional groups, suitable surface properties, and the nanoporous structure of the coating.