Nucleation and growth of apatite on an anatase layer irradiated with UV light under different environmental conditions

Implant surfaces must sometimes be modified to form strong bonds to host tissues. The method of depositing an anatase layer on chemically pure titanium by chemical oxidation with H₂O₂ and subsequent calcination (CHT) is known to deposit apatite under physiological conditions; it thus exhibits bone-bonding ability. UV irradiation should affect the bonding ability because the CHT anatase layer would experience certain chemical modifications, such as a decrease or an increase in the number of Ti-OH and Ti-O(H)-Ti sites; these sites are considered active sites for apatite nucleation. When in vitro apatite deposition was examined, using Kokubo's simulated body fluid, UV irradiation in air reduced the apatite-forming ability of the CHT anatase layer, and UV irradiation on the samples in water enhanced the ability. These results were correlated to changes in the Ti-OH and Ti-O(H)-Ti sites, as determined by O 1s X-ray photoelectron spectroscopy. Analysis of the number and size of the semi-spherical apatite particles and their surface coverage led to a model: proper assembly of the Ti-OH and Ti-O(H)-Ti sites should only give rise to the induction of apatite nucleation, analogous to topotaxy effects.