Biomimetic apatite induction of P-containing titania formed by micro-arc oxidation before and after hydrothermal treatment

Phosphorous (P)-containing titania films were prepared by micro-arc oxidation (MAO) of titanium (Ti) in an electrolyte containing β-glycerol phosphate disodium salt pentahydrate (β-GP, C3H7Na2O6P.5H2O), and their apatite inducing ability in a simulated body fluid (SBF) was investigated. Macro-porous titania films were formed, consisting of only anatase phase, and the P content in the films increased up to 8 at.% with an increasing applied voltage. During hydrothermal treatment, the P in the films was diffused out to the surface and hydrolyzed to form the hydrogen phosphate (HPO42−) group. When immersed in SBF, no apatite was induced in any of the P-containing MAO specimens for up to 28 days. However, after a hydrothermal treatment at 250 °C, apatite was induced on the titania surfaces as early as 9 h immersion, and the entire exposed surface was covered with the apatite globules after 36 h immersion, which was much faster than the apatite induction on Ca-containing titania. The higher apatite-inducing ability of P-containing titania after hydrothermal treatment was believed to be due to the crystal structure (anatase) and presence of HPO42− group on the surface.