Synthesis method of hydroxyapatite: A review

Hydroxyapatite (HAp) is most common calcium phosphate ceramic that is used in biomedical applications owing to its chemical composition, which is similar to human bone and teeth. Hydroxyapatite can be synthesised using chemical precursors, especially calcium and phosphorus, using various methods including, dry, wet, thermal, or a combination of these methods. Instead of using chemical synthesis, HAp can also be extracted from natural sources, such as animal bones and scales which are rich in HAp content. Different synthesising methods result in different morphologies, sizes, and phase crystallinities. The concern of achieving a nano-sized HAp has attracted a great deal of attention owing to the human bone HAp is in nano-size range, and the nano size HAp has excellent clinical performance compared to micron-sized HAp. Furthermore, production of nano-size HAp improves cell proliferation and cellular activity in bone growth, which makes it more suitable as biomaterials for bone implants. Thus, various parameters were studied to achieve a composition of HAp that is like the HAp in human bone and teeth. This review summaries various methods of synthesising the HAp, which includes dry, wet, thermal, and a combination of these methods.