Effect of autoclave and hot water treatments on surface structure and in vitro apatite-forming ability of NaOH- and heat-treated bioactive titanium metal

Sodium hydroxide (NaOH)-, heat- and autoclave-treated Ti metal did not form apatite in simulated body fluid (SBF) within 604.8 ks, although some Na remained on the Ti metal surface after the autoclave treatment. When hot water treatment was applied between NaOH and heat treatments, the Ti metal formed apatite within 604.8 ks in SBF. While anatase TiO₂ was partially precipitated by the NaOH and heat treatments, it disappeared after subsequent autoclave treatment. By adding hot water treatment between the NaOH and heat treatments, a considerable amount of anatase TiO₂ was formed, which remained after the autoclave treatment; the zeta potential of Ti metal was almost zero in SBF. These results indicate that with intermediate hot water treatment, Ti metal can form apatite in SBF even after autoclave treatment. Anatase TiO₂, rather than the amount of Na or the zeta potential in SBF, might play an important role in apatite formation.