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Calcium phosphate cements are of great interest for researchers and their applications in medical practice expanded. Nevertheless, they have a number of drawbacks including the insufficient level of mechanical properties and low degradation rate. Struvite (MgNH4PO4) -based cements, which grew in popularity in recent years, despite their neutral pH and acceptable mechanical performance, release undesirable NH4+ ions during their resorption. This issue could be avoided by replacement of ammonia ions in the cement liquid with sodium, however, such cements have a pH values of 9–10, leading to cytotoxicity.Thus, the main goal of this investigation is to optimize the composition of cements to achieve the combination of desirable properties: neutral pH, sufficient mechanical properties, and the absence of cytotoxicity, applying Na2HPO4-based cement liquid. For this purpose, cement powders precursors in the CaO–MgO–P2O5 system were synthesized by one-pot process in a wide composition range, and their properties were investigated.The optimal performance was observed for the cements with (Ca + Mg)/P ratio of 1.67, which are characterized by newberyite phase formation during setting reaction, pH values close to 7, sufficient compressive strength up to 22 ± 3 MPa (for 20 mol.% of Mg), dense microstructure and adequate matrix properties of the surface. This set of features make those materials promising candidates for medical applications.

Al-substituted hydroxyapatite (Al-HA) powders with apatite structure and particle size of 30–70 nm were obtained via precipitation method. The effect of Al content on specific surface area and morphology of powders was studied, and a formation of highly anisotropic phase due to Al doping was observed. The influence of heat treatment in 300–1400 °C range on the phase composition, lattice parameters, Fourier-transform infrared spectroscopy (FTIR) spectra and mass loss of powders was investigated. Introduction of Al in the hydroxyapatite (HA) lattice in the range 0.5–1.0 mol.% resulted in the improvement in thermal stability, which had not been reported previously. Incorporation of 5–10 mol.% of Al resulted in the formation of biphasic materials based on HA and whitlockite-like structure at 900 °C and apatite and α- tricalcium phosphate (α-TCP) phases at 1200–1400 °C. Introduction of 20 mol.% of Al resulted in the formation of isomorphic Al-substituted whitlockite phase Ca9Al(PO4)7. We have estimated the onset of Ca9Al(PO4)7 transformation into α-TCP phase at 1400 °C. Keywords: Al-substituted hydroxyapatite, Phase transformation, Thermal stability