Synthesis of weakly crystallized hydroxyapatite with Zn substitution and its effect on the calcium phosphate and calcium sulfate cements

Zn is an essential trace element in the normal growth and loading Zn into biomaterials for biomedical applications has always been a hot topic due to its immune regulation. The preparation and characterization of Zn-substituted weakly crystallized hydroxyapatite (WCH) are studied in this work, and Zn-substituted WCH was added to calcium phosphate and calcium sulfate cements (CPC and CSC) to address the effect of Zn²⁺ on the hydration crystallization behavior of calcium phosphate and calcium sulfate. Our results demonstrate that Zn²⁺ will inhibit the transformation of α-TCP to HA during the hydration reaction of CPC. And the adding of Zn²⁺ in CSC changed the crystallization morphology of calcium sulfate. The regulation of Zn on the crystallization behavior of calcium phosphate and calcium sulfate resulted in the different in vitro degradation behaviors of CPC and CSC. With the purpose of improving the biological effects of materials, the polarization of Zn²⁺ released from cements on macrophages was also characterized in this work, and the results showed that appropriate concentrations of Zn²⁺ can inhibit inflammation after stimulating RAW264.7 cells for an appropriate period of time. The presented results may be useful guidelines for the preparation and design of composite bone cement with specific Zn content.