Sr-containing biphasic calcium phosphate bioceramic granules: physicochemical characterization, ion release, and in vitro cytocompatibility

In this study, the favorable properties of biphasic calcium phosphates (BCP) with the biological benefits of Sr 2+ ion release were combined in bioceramic granules. BCP was selected as the base material due to its tunable phase composition and established applications in bone regeneration. The bioceramic granules, with sizes ranging from 0.5 to 1 mm, were prepared using extrusion of the as-synthesized and filtered calcium-deficient hydroxyapatite (CDHAp) precipitates, followed by high-temperature sintering at 1150 o C. The granules were produced with various phase compositions, including hydroxyapatite (HAp), β-tricalcium phosphate (β-TCP), and BCP (HAp/β-TCP (70/30, 50/50, and 30/70 wt%)). The CDHAp precipitates containing 5 wt% of Sr were used to obtain Sr-containing BCP (SrBCP) bioceramic granules. Sr was incorporated at 5 wt% based on previous reports identifying this level as biologically effective. Physicochemical properties of the prepared granules were characterized using X-ray diffraction (XRD), atomic absorption spectrometry (AAS), Fourier transform infrared spectroscopy (FTIR), micro-computed tomography (μCT), Brunauer-Emmett-Teller (BET) method, and field emission scanning electron microscopy (FE-SEM), with particular evaluation of in vitro degradation, including Ca 2+ and Sr 2+ ion release profiles and granule microstructural changes, and in vitro cell morphology and proliferation. The influence of chemical and phase compositions on the morphology and proliferation of osteoblastic MG-63 cells was evaluated. The phase composition significantly influenced the bioceramic granules' microstructure, whereas the addition of Sr had minimal impact. In vitro degradation under physiological conditions (TRIS-HCl, pH 7.45, 37 °C) revealed that SrBCP bioceramic granules provide a sustained, low-concentration (up to 1.5 μg/mL in 24 h) release of Sr 2+ ions for up to 25 days. Regardless of their phase and chemical composition, the bioceramics supported MG-63 cell adhesion. Cell proliferation was strongly correlated with the solubility of the bioceramics and the release of Sr 2+ ions. The presence of Sr 2+ ions positively impacted cell proliferation.