Hydroxyapatite (HAp) is a calcium phosphate like the human hard tissues in morphology and composition, whose chemical formula is Ca10 (PO4)6 (OH)2. HAp has a hexagonal structure and its stoichiometric Ca/P ratio is 1.67. HAp is the main inorganic component of the mineral part of bone and teeth. Thermodynamically, HAp is the most stable calcium phosphate compound under physiological conditions. HAp has long been among the most studied biomaterials for both its proven biocompatibility and its stability.
With the development of nanotechnology, the impact of nanomaterials on medicine, food and manufacturing industry has been widely concerned. Nano-hydroxyapatite (nano-HAp) is an attractive biomaterial due to its similarity in size, crystallography, and chemical composition with human hard tissue and its biocompatibility, bioactivity, osteoconductivity, non-toxicity, non-inflammatory nature, and other outstanding properties. Nano-HAp is extensively used for bone treatment, controlled drug release, toothpaste additive, and dental implants.
HAp is often used as a coating over titanium and stainless-steel implants to reduce the rate of implant rejection. HAp in powder, lump or bead form can be used directly to repair bone holes or defects. Due to its bioactivity, HAp can promote bone growth and repair to shorten healing time.
The enamel consists of 97 wt.% nano-HAp and 3 wt.% organic material and water. In dentin, the nano-HAp represents 70 wt.%. Nano-HAp gives an appearance of bright white and eliminates the diffuse reflectivity of light by closing the small pores of the enamel surface. Nano-HAp added to toothpaste and mouthwash can facilitate the repair of demineralized enamel or dentin surfaces by depositing at defects.
It has been found that nano-structured composite air filters containing HAp can effectively absorb and decompose CO to reduce automobile exhaust pollutants. In addition, alginate/nano- HAp composite can be used to remove fluoride through an ion exchange mechanism, with biocompatibility and biodegradability. Recently, applications of nano calcium phosphate in catalysis and protein separation have been developed. These studies indicate that HAp-based materials have broad application prospects.