Multisubstituted hydroxyapatite powders and coatings: The influence of the codoping on the hydroxyapatite performances

The biological apatite, whose the bone and teeth mineral phases are composed, remarkably differs from stoichiometric hydroxyapatite (HAp, Ca-10(PO4)(6)(OH)(2), Ca/P = 1.667). Indeed, it consists in carbonated Ca-deficient (Ca/P < 1.667) apatite, characterised by the presence of several vicarious ions, either incorporated within the apatite lattice or just adsorbed on the crystal surface, including anionic (eg, F-, Cl-, SiO44- and CO3=) and/or cationic substitutions (eg, Na+, Mg2+, K+, Sr2+, Zn2+, Ba2+, Al3+). For this reason, recently, a continuous and rising attention has been devoted to the ionic substitutions within the hydroxyapatite lattice in order to resemble the chemical composition of the bone mineral component and to improve its chemical, physical and mostly biological properties, for applications in biomedical sector, particularly in dentistry, orthopaedics and bone tissue engineering. The present manuscript provides a complete overview about the bi-substituted hydroxyapatites in form of powders and coatings, in order to evidence the effect of the co-doping with different vicarious ions within HAp lattice on its physicochemical properties, such as microstructure, morphology, thermal stability, solubility, thermal decomposition, dissolution, grain size, mechanical strength, degradation kinetics, corrosion resistance, and biological responsiveness, in terms of in vitro bioactivity, cytotoxicity and antibacterial action.