Relationship between valence of titania and apatite mineralization behavior in simulated body environment

Abstract Titania‐based materials are attractive for hard tissue repair due to their bone‐bonding ability induced by apatite formation in the body environment. Various surface treatments have therefore been developed to produce a hydrated titania layer on Ti and its alloys. Titania takes various valences, such as TiO (Ti 2+ ) and Ti 2 O 3 (Ti 3+ ), as well as typical TiO 2 (Ti 4+ ); however, there is no comprehensive study of structural effects on the apatite‐forming ability of these titanias. In this study, we investigated apatite formation on titania powders with various valences in simulated body fluid. Anatase‐ and rutile‐type TiO 2 formed apatite in simulated body fluid within 7 days, but TiO and Ti 2 O 3 did not. In contrast, when the titania powders were treated with NaOH solution, the surface converted to tetravalent titania and all samples formed apatite. It is proposed that the surface electrical states of TiO and Ti 2 O 3 are strongly affected by their bulk conductivity and that these behaved like pure Ti metal, which has poor apatite‐forming ability. Apatite formation was favorable when the titania had a high absolute value and exhibited high fluctuations of zeta potential during initial stages in simulated body fluid, owing to adsorption of large amounts of Ca 2+ and HPO 4 2− .