Silicon-containing Apatites

Researchers have used a variety of methods to enhance the performance of hydroxyapatite (HA) as a bone graft material. These include, among other methods, porosity optimization, in combination with various proportions of other calcium phosphate phases such as beta-tricalcium phosphate (ß-TCP), or by adsorption of various growth factors on the surface. Another approach is to change the chemistry of HA. The modification of HA by the substitution of relatively small amounts (<2 wt%) of silicon, in the form of silicate ions, for phosphate ions effects a significant change in its properties. A variety of studies have reported the effect of silicon-substituted HA (Si-HA) ceramics on surface charge, grain size, dissolution in vitro and in vivo, osteoblast cell growth, and bone repair in vivo. This 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. An overview of a related system, namely silicon-stabilized TCP, is also provided. In addition to reviewing the current status of silicon-substituted calcium phosphate ceramics, this chapter offers a view of the future requirements of research in this field.