Synthesis methods of hydroxyapatite and biomedical applications: an updated review

Hydroxyapatite (HAp) is observed as a mineral deposition on bones and in teeth enamel and hence serves as an ideal model or as a component for orthopaedic and dental implants. Synthetic HAp has been synthesized on a lab scale for several decades to mimic the naturally occurring HAp based on its chemical and crystallographic nature. There are several methods for synthesis of HAp available in the literature, amongst which the following are a few examples: dry methods which include the solid-state method and mechano-chemical method, wet methods which include chemical precipitation and sol–gel method, and methods which use high-temperature such as combustion method and pyrolysis method. However, more economical and better yield-giving methods produce HAp with controlled morphology for its potential use in biomedical applications. One such method that exploits Schiff base ligands to form chelating complexes with calcium and phosphate precursors and protect generated HAp nuclei is recent ongoing research for the preparation of HAp. This review presents the synthesis of HAp using a wide array of methods, with the recent HAp using novel methods compared to the traditional synthesis of HAp.