Influence of gallium doping on the thermal stability and microstructure of sintered hydroxyapatite bioceramics

Calcium phosphates (CaPs) are extensively used in the biomedical field for bone regeneration applications. Hydroxyapatite (HAp), the main component of human bone, has been successfully used as a bone graft material. Partial calcium (Ca) substitution with gallium (Ga) can influence HAp's physicochemical properties and biological activity. In this study, Ga-doped Ca-deficient HAp (GaCDHAp) powders containing 1.6 ± 0.1 and 3.3 ± 0.4 wt% Ga were synthesized using wet chemical precipitation. Bioceramics were prepared from the synthesized GaCDHAp powders using uniaxial compaction and sintering at temperatures between 600 and 1200 °C. The quantitative phase composition and the Ga substitution in the HAp lattice were investigated by Rietveld refinement. It was observed that the sintering of the GaCDHAp led to the formation of biphasic CaP bioceramics composed of HAp and α-TCP. The secondary phase inhibited the densification, leading to a microporous structure of GaHAp bioceramics. Structure refinement showed that Ga substituted Ca on the Ca1 site in the HAp lattice. Charge balance was maintained by an additional partially occupied oxygen site in the structural channel.