Silicon-containing apatites

Researchers have used a variety of methods to enhance the performance of hydroxyapatite as a bone graft material including, among other methods, optimizing porosity, combining it with various proportions of other calcium phosphate phases such as Β-TCP, or by adsorbing various growth factors to the surface. Another approach is to change the chemistry of hydroxyapatite. The modification of hydroxyapatite by the substitution of relatively small amounts (less than 2 wt%) of silicon, in the form of silicate ions, for phosphate ions significantly changes its properties. A variety of studies have reported the effect of silicon-substituted hydroxyapatite (Si-HA) ceramics on surface charge; grain size; dissolution in vitro and in vivo; osteoblast cell growth; bone repair in vivo. This updated review summarizes these studies, including the synthesis of Si-HA, the formation of Si-HA coatings and porous scaffolds, and their biological behavior, and attempts to correlate physiochemical properties with in vitro and in vivo observations. Since the original version of this chapter there have been a significant number of in vitro and in vivo studies that aim to understand what role silicate substitution may have on the biological behavior of hydroxyapatite. An overview of a related system, namely silicon-stabilized tricalcium phosphate is also provided. In addition to reviewing the current status of silicon-substituted calcium phosphate ceramics, this review finishes with a view of the future requirements of research in this field.