An effective approach by a chelate reaction in optimizing the setting process of strontium-incorporated calcium phosphate bone cement

Strontium (Sr) plays a special role in enhancing the biological osteo-stimulation of calcium phosphate cement (CPC), not only increasing osteoblast-related gene expression and the alkaline phosphatase (ALP) activity of mesenchymal stem cells (MSCs), but also inhibiting the differentiation of osteoclasts. However, the incorporation of Sr unfortunately delays the setting of CPC and weakens its mechanical properties. The purpose of this study was to overcome the aforementioned problems by introducing a chelate reaction between Ca/Sr cations from the original solid phases and carboxyl groups from the liquid phases. As expected, the setting process of Sr-incorporated CPC was optimized and the cement body after rapid hardening was mostly consisting of unreacted original solid phases. After soaking in simulated body fluid for 14 and 28 days, the composition of the cement body gradually converted to the most thermodynamic stable phase, hydroxyapatite, indicating an in vitro bioactivity. The compressive strength was not impaired in the Sr-incorporated groups, but rather, further increased over time. Higher cell proliferation rate and better ALP activity of MG-63 cells cultured on the cement surface were obtained with the presence of Sr content, demonstrating potential abilities to favor new bone formation.