Biomimetic apatite formation on chemically treated titanium.

Titanium treated in NaOH can form hydroxycarbonated apatite (HCA) after exposition in simulated body fluid (SBF). Generally, titanium is covered with a passive oxide layer. In NaOH this passive film dissolves and an amorphous layer containing alkali ions is formed on the surface. When exposed to SBF, the alkali ions are released from the amorphous layer and hydronium ions enter into the surface layer, resulting in the formation of Ti-OH groups in the surface. The released Na(+) ions increase the degree of supersaturation of the soaking solution with respect to apatite by increasing pH, and Ti-OH groups induce apatite nucleation on the titanium surface. The acid etching of titanium in HCl under inert atmosphere was examined as a pretreatment to obtain a uniform initial titanium surface before alkali treatment. Acid etching in HCl leads to the formation of a micro-roughened surface, which remains after alkali treatment in NaOH. It was shown by SEM, gravimetric and solution analysis that the apatite nucleation was uniform and the thickness of precipitated HCA layer increased continuously with time. The treatment of titanium by acid etching in HCl and subsequently in NaOH is a suitable method for providing the metal implant with bone-bonding ability.