Hydroxyapatite/tannic acid composite coating formation based on Ti modified by TiO2 nanotubes

Oxidative stress induced by reactive oxygen species (ROS) overproduction and accumulation would hinder the osseointegration process at the bone-implant interface, leading to a higher rate of implant failure. To endow titanium (Ti) implants with antioxidant activity, we developed a coating approach mediated by tannic acid (TA)-Ca2+ coordination complexation. A hydroxyapatite (HA)/TA composite coating was prepared, based on Ti substrates modified by anodized and annealed titanium dioxide (TiO2) nanotube arrays. The results reveal that highly ordered TiO2 nanotubes with a diameter of 142.23 ± 14.52 nm and a length of 374.17 ± 42.47 nm were fabricated on the Ti substrate and the XRD pattern shows the TiO2 anatase phase after annealing at 450 ℃. TA-Ca complexes were formed on the surface of TiO2 nanotubes by immersing the constructs into the mixed solution of TA and CaCl2, where they are served as calcium sites for the HA growth by later phosphorylation. The HA nanoparticles present needle-shape with the diameter of 18 ∼ 20 nm. The total antioxidant capacity assay was employed to confirm the antioxidant effect of the HA/TA composite coating. The results indicate that it has a persistent and strong antioxidative activity. In vitro cytological test results show that HA/TA coating exhibits good cytocompatibility for osteoblasts proliferation and adhesion.