hydroksiapatiitit

Hydroksiapatiitit, known in English as hydroxyapatites, are a family of calcium phosphate materials with the idealized formula Ca10(PO4)6(OH)2. They occur naturally as the mineral hydroxyapatite and are produced synthetically for a range of biomedical applications. In biology, bone mineral and tooth enamel contain a non-stoichiometric, carbonate-substituted form of hydroxyapatite, commonly referred to as biological apatite.

Structure and substitutions: Biological apatite typically includes carbonate and trace ion substitutions (such as Na+, Mg2+, and F−), which lower crystallinity and increase solubility relative to the pure Ca10(PO4)6(OH)2. These substitutions influence remodeling, mineralization, and the material’s bioactivity.

Properties: Hydroxyapatite is biocompatible and bioactive, supporting bone cell attachment and growth. It is osteoconductive, providing a scaffold for new bone to form. Synthetic variants can be produced as nanoscale powders, dense ceramics, or porous scaffolds. The material is relatively stable at physiological pH but dissolves under acidic conditions, a property exploited in some medical applications.

Production and forms: It can be synthesized by wet chemical precipitation from calcium and phosphate precursors at alkaline pH, and by hydrothermal, solvothermal, or sol-gel methods. Densified ceramics are made by sintering, while porous forms are used for scaffolds and bone graft substitutes.

Applications: Hydroxyapatite is used as bone graft substitutes, dental coatings for implants, and as coatings on metal devices to improve bonding. It also serves as a bioactive filler in composites and as a carrier for localized drug delivery; nanoscale hydroxyapatite is studied for enamel remineralization and bone tissue engineering.