Inhibitory Effects of Doped Aluminum and Silicon on HAp-Forming Ability of Titania in Simulated Body Fluid

Abstract

Chemical modification of titanium substrate provides ability of hydroxyapatite (HAp) formation that is important property for bone-bonding capability after implantation in bony defects. Potential of the HAp-formation is occasionally reduced. In the present study, we investigated potential of the HAp-formation on titanium oxide (titania) with doped silicon or aluminum in simulated body fluid (SBF). Sol-gel processing was applied to prepare titania with doped silicon (TSx) or aluminum (TAx), in its nominal composition ranging from 0 to 10 mol%. Specific surface area of the prepared samples was gradually increased with increasing the amounts of silicon or aluminum. Zeta potential of TAx was definite changed from negative charge to positive charge with increasing aluminum amounts, but TSx slightly changed to be positive with increasing silicon amounts. The pure titania sample free from doping of silicon or aluminum showed formation of calcium phosphate precipitates, that is HAp-formation, after soaking in SBF for 14 d. In contrast, all the titania samples with doped silicon or aluminum hardly showed evidence of precipitates of calcium phosphates, although absorption of calcium and phosphate ions were detected. Especially, TAx showed remarkable adsorption of phosphate ions. Aluminum-doping in titania enhances the adsorption of phosphate ion on the surface, but reduce nucleation rate of calcium phosphates in body environment.