Nanosize hydroxyapatite: doping with various ions

Natural crystal sizes of bone minerals are present in the nanoscale regime (specifically less than 100 nm in at least one direction). Therefore, research on the synthesis and characterisation of nanosize hydroxyapatite has gained significant importance in numerous biomedical applications. This is because currently used pure micrometre sized hydroxyapatite has poor mechanical properties, which limits it use in non-load bearing applications. For these reasons, various ions could be easily substituted into nanostructured hydroxyapatite to alter its biocompatibility, sinterability and mechanical properties. In this study, the synthesis methods, biocompatibility, physical, microstructural and nanostructural characteristics of nanocrystalline hydroxyapatite are reviewed. Compared to pure micrometre structured hydroxyapatite, numerous properties (most notably, biocompatibility properties pertinent for orthopedic applications) are improved for nanostructured hydroxyapatite doped with various ions. Such studies demonstrated that the mechanical properties and phase stability of nanohydroxyapatite doped with various ions after sintering at high temperatures should be investigated in more detail.