Nucleation and growth of apatite on amorphous phases in simulated body fluid

The essential requirement for an artificial material to bond to living bone is the formation of a bonelike apatite layer on its surface in the living body. The present paper shows that some functional groups such as Si-OH, Ti-OH, Zr-OH, Ta-OH and Nb-OH on a material are effective for the apatite nucleation in body environment. These functional groups induce the apatite nucleation not directly but through formation of a calcium compound such as calcium silicate or titanate. Once the apatite nuclei are formed, they can grow spontaneously by consuming the calcium and phosphate ions from the surrounding fluid. Their growth is controlled not by ion diffusion in the fluid, but by the mass transport across the solid-liquid interface. These fundamental findings provide us principles for developing various kinds of bioactive materials with different mechanical properties.