Initial nucleation process of hydroxyapatite on organosilane self-assembled monolayers

Initial nucleation process of hydroxyapatite (HAp) formed from simulated bo dy fluid (SBF) was investigated on Si substrates on which self-assembled mo nolayers (SAM) of 3-aminopropyltriethoxysilane (APTS) and trimethylchlorosi lane (TMCS) were formed. The synthesized HAp appeared hemispherical shape c omposed of tiny plate-like particles. Nucleation of HAp was formed just in the early stage, and then the nucleated HAp proceeded to growth process. Sa turated number density of HAp particles was ca. 10(5) to 10(6)/cm(2). Satur ated number density increased with increasing calcium ion and phosphate ion concentrations in SBF, and showed slight dependence on the kind of SAM, or dered as OH is approximately equal to CH3 > NN2. These results indicate tha t depletion of calcium and phosphate ions in the vicinity of substrates sho uld limit nucleation while growth of particles continues. Depletion factor in the modified nucleation rate formula gives the saturated nucleation dens ity. It is indicated that the minimum ionic concentration for HAp nucleatio n depends on the kind of SAR I.