Nanotube-formed Ti substrates coated with silicate/silver co-doped hydroxyapatite as prospective materials for bone implants

The adhesion strength, antibacterial property, biocompatibility and corrosion resistance of implant coating materials remain challenging. In this study, a novel silver-doped hydroxyapatite/calcium silicate (AgHA/CS) layer was deposited on Ti modified with TiO2 nanotube (TN) through electrodeposition (ED) combined with anodisation. The TN under layer possessed a compact structure and diameter of approximately 100 nm. The AgHA/CS overlayer presented a porous structure and pore size distribution of 30-50 μm. Ag was incorporated into HA coating to improve the antimicrobial properties. Si was added as a second binary element to offset the potential cytotoxicity of Ag. Results highlight that Si4+ and Ag+ could be evenly incorporated into the AgHA/CS coating. The adhesion strength of AgHA/CS/TN significantly increased because of the interlocking of the roughened surface with bioceramic particles that entered into the voids of the TiO2 nanotubes. Potentiodynamic polarisation and electrochemical impedance spectrum tests revealed that the corrosion resistance increased after AgHA/CS/TN coating. The coating with the highest corrosion resistance also demonstrated excellent wettability (contact angle, 0°) and apatite-forming ability under bioactivity test. Cytotoxicity tests indicated that the AgHA/CS/TN coating enabled higher cell viability compared with the uncoated sample. In addition, the HA and AgHA/CS/TNA coatings considerably improved cell differentiation ability than that of the uncoated sample. The as-prepared AgHA/CS/TN biocomposite coatings effectively prevented the proliferation and biofilm formation of Staphylococcus aureus. With their superior mechanical properties, satisfactory osseo-integrative potential and excellent antibacterial properties, AgHA/CS/TN multifunctional biomaterials exhibit potential for orthopaedic surgeries.