Plasma-treated nanostructured TiO2 surface supporting biomimetic growth of apatite

Although some types of TiO2 powders and gel-derived films can exhibit bioactivity, plasma-sprayed TiO2 coatings are always bioinert, thereby hampering wider applications in bone implants. We have successfully produced a bioactive nanostructured TiO2 surface with grain size smaller than 50 nm using nanoparticle plasma spraying followed by hydrogen plasma immersion ion implantation (PIII). The hydrogen PIII nano-TiO2 coating can induce bone-like apatite formation on its surface after immersion in a simulated body fluid. In contrast, apatite cannot form on either the as-sprayed TiO2 surfaces (both <50 nm grain size and >50 nm grain size) or hydrogen-implanted TiO2 with grain size larger than 50 nm. Hence, both a hydrogenated surface that gives rise to negatively charged functional groups on the surface and small grain size (<50 nm) that enhances surface adsorption are crucial to the growth of apatite. Introduction of surface bioactivity to plasma-sprayed TiO2 coatings, which are generally recognized to have excellent biocompatibility and corrosion resistance as well as high bonding to titanium alloys, makes them more superior than many current biomedical coatings.