Octacalcium phosphate (OCP, Ca₈H₂(PO₄)₆·5H₂O) is known to be a possible precursor of biological hydroxyapatite formation of organic bone tissue. OCP has higher biocompatibility and osseointegration rate compared to other calcium phosphates. In this work, the synthesis of low-temperature calcium phosphate compounds and substituted forms of those at physiological temperatures is shown. Strontium is used to improve bioactive properties of the material. Strontium was inserted into the OCP structure by ionic substitution in solutions. The processes of phase formation of low-temperature OCP with theoretical substitution of strontium for calcium up to 50 at.% in conditions close to physiological, i.e., temperature 35–37 °C and normal pressure, were described. The effect of strontium substitution range on changes in the crystal lattice of materials, the microstructural features, surface morphology and biological properties in vitro has been established. The results of the study indicate the effectiveness of using strontium in OCP for improving biocompatibility of OCP based composite materials intended for bone repair.

Octacalcium phosphate is the precursor of biological apatite, that is why it is of special interest in bone regeneration due to it’s biocompatibility and biodegradability. This study was performed to examine the in vitro stability of octacalcium phosphate granules in physiological solutions. Powder X-ray diffraction (XRD), infrared spectroscopy (IR), plasma atomic emission spectroscopy (AES) and scanning electron microscopy (SEM) data were obtained before and after granules immersion. The variation of Ca²⁺ and HPO₄ ^2- concentration in the soaking solutions suggests that the material transformation occurs through octacalcium phosphate dissolution followed by hydroxyapatite precipitation.