Nanostructured positively charged bioactive TiO2 layer formed on Ti metal by NaOH, acid and heat treatments.

Nanometer-scale roughness was generated on the surface of titanium (Ti) metal by NaOH treatment and remained after subsequent acid treatment with HCl, HNO(3) or H(2)SO(4) solution, as long as the acid concentration was not high. It also remained after heat treatment. Sodium hydrogen titanate produced by NaOH treatment was transformed into hydrogen titanate after subsequent acid treatment as long as the acid concentration was not high. The hydrogen titanate was then transformed into titanium oxide (TiO(2)) of anatase and rutile by heat treatment. Treated Ti metals exhibited high apatite-forming abilities in a simulated body fluid especially when the acid concentration was greater than 10 mM, irrespective of the type of acid solutions used. This high apatite-forming ability was maintained in humid environments for long periods. The high apatite-forming ability was attributed to the positive surface charge that formed on the TiO(2) layer and not to the surface roughness or a specific crystalline phase. This positively charged TiO(2) induced apatite formation by first selectively adsorbing negatively charged phosphate ions followed by positively charged calcium ions. Apatite formation is expected on the surfaces of such treated Ti metals after short periods, even in living systems. The bonding of metal to living bone is also expected to take place through this apatite layer.