Natural and Synthetic Hydroxyapatites

Hydroxyapatite is a specific calcium phosphate phase that can occur naturally or can be synthesized using a variety of methods. Importantly it is similar in chemical and phase composition to the inorganic mineral component of bone and teeth. It has therefore been studied extensively as a biomaterial and has found applications alone or in combination with other materials to produce medical devices. This chapter reviews the various synthesis methods that have been utilised to produce hydroxyapatite, including comparisons with naturally occurring hydroxyapatites, the potential to substitute various ions in the hydroxyapatite structure, and the ability to control physical properties of the resulting material, including porosity and crystallite size and morphology. It also includes a review of the various methods for characterising these materials, including chemical, physical and biological characterisation. Although hydroxyapatite-based medical devices have been used clinically for many decades, it is clear that there is still much to learn about the factors such as composition and microstructure that can illicit various responses in vivo and how these may be best harnessed in the design of new materials for use as biomaterials.