Development of Sr and CO₃ co-substituted hydroxyapatites for biomedical applications

Sr and CO₃ co-substituted hydroxyapatite (SrCHA) nanopowder was synthesized by neutralization. The powder was characterized. The improved solubility in Hanks' balanced solution of SrCHA granules (400-600 μm of dimensional range), potentially usable as bone filler, was assessed and compared with that of an analogous carbonate free granulate. SrCHA porous bodies with interconnected micro- and macro-porosity, which mimic the morphology of spongy bone, were prepared by the impregnation of cellulose sponges with suspensions of the SrCHA powder and controlled sintering. SrCHA porous scaffolds sintered at 850 °C, in flowing CO₂ atmosphere, showed satisfying compressive strength (4.58 ± 0.75 MPa) for a porosity value of 45 vol.% and retained the desired ionic substitutions (Sr/Ca = 0.11 and CO₃ = 6.8 wt.%). The possibility of widely modulating, by acting on the chemical-physical-geometrical features of the material, the prolonged in situ release of therapeutic Sr, together with the fundamental (Ca, PO₄) and main substituting (CO₃) ions that constitute the bone mineral phase, makes the use of SrCHA as resorbable bone filler or bone substitute scaffolds promising, especially when pathologies related with Sr deficiency are present. In vitro and in vivo tests are in progress.