Ionic substitutions in calcium phosphates synthesized at low temperature

Low-temperature densification of Mg-doped hydroxyapatite fine powders under hydrothermal hot processing conditions

“…Nevertheless, the apparent density values of the MgHA4 pellets were somewhat lower (< 2.9844 ± 0.018 g/cm 3 ) than the apparent density values achieved at higher temperatures (3.0425 ± 0.024 g/cm 3 , 240 ºC, Table 2). By contrast, powders containing 2 (MgHA1, ) and 4 (MgHA2, ) mol % Mg with fine particle sizes (39 and 32 nm) did not exhibit a systematic increase in their apparent density by increasing the reaction time to 6 h. These particles are chemically more stable than particles containing 6 mol % Mg.…”

“…The results indicate that the densification temperature was the most important parameter for the rapid densification of MgHA powders, contrary not the reaction time or water content, which both had no effect. Controlling the temperature led to highly dense MgHA pellets with an apparent density up to 3.0758 ± 0.001 g/cm 3 , near the theoretical density value of the HA (3.156 g/cm 3 ). This dense specimen was obtained at 240 ºC after 6 h using a water content of 10 wt%.…”

“…For comparison purposes, the apparent density of all MgHA compacts was carried out using a helium pycnometer (Multipycnometer Quantachrome, USA). Prior to the density measurements, calibration of the pycnometer was carried out using a standard stainless steel sphere with a volume of 56.5592 cm 3 , which was located inside the measuring cell (volume 135 cm 3 ). The MgHA compacts were previously weighed, and their volume was measured four times at a helium pressure of 0.117 MPa and the average apparent density value was calculated for each sample.…”

“…In vivo studies have demonstrated that the presence of Mg in HA improves cell behaviour, adhesion with synthetic hard tissues, proliferation, and metabolic activation [12]. For these reasons, Mg is an interesting element to study regarding its possible ionic substitutions into the HA structure [3,[13][14][15].…”

“…The incorporation of ions at various concentrations in the hexagonal structure (i.e., A, B or X sites) of HA determines its crystallinity and non-stoichiometry. Ionic substitutions (e.g., Mg 2+ , Zn 2+ , Sr 2+ , Si 4+ and Mn 2+ ) in the HA structure have been reported to improve the biological performance of calcium phosphate phases, thereby enhancing osseointegration, mechanical strength and implantation efficiency [3,4]. Furthermore, changes in the chemical composition of HA influence its physical, chemical and physiological properties, which consequently have an effect on biomineralisation processes, bioactivity enhancement, and ion delivery for treating bone diseases [3,4].…”