Effects of Zn/Sr co-substitution on the physicochemical properties and cellular responses of wollastonite

Wollastonite (CaSiO3, CS) has shown a great potential as a bone biomaterial due to its favorable degradation behavior and the beneficial silicon and calcium ions released during its degradation. However, the rapid degradation of CS may result in a rapid increase in local pH values and lead to cell death. To address this issue and further enhance the biocompatibility, osteogenic, angiogenic, and osteoclast differentiation inhibitory properties of CS; zinc (Zn) and strontium (Sr) ions were introduced into CS through an ion-doping method. The effects of Zn doping, Sr doping, and Zn/Sr co-doping on the crystal structure, in vitro mineralization, and cellular responses of CS were systematically investigated. The results indicated that Zn doping and Sr doping had no significant effect on the phase of CS, while Zn/Sr co-doping promoted the substitution of Zn and Sr ions for calcium ions. Moreover, the introduction of Zn and Sr ions slowed the degradation process of CS and inhibited its in vitro mineralization activity. Furthermore, while Zn doping and Sr doping significantly enhanced the cytocompatibility and osteogenesis of CS, respectively, Zn/Sr co-doping exhibited synergistic effects in enhancing the osteogenesis of CS. Interestingly, the introduction of Zn and Sr ions also improved the angiogenic properties of CS and increased its ability to inhibit osteoclast differentiation; however, there was no significant synergistic effect between Zn doping and Sr doping on these properties. In conclusion, Zn/Sr co-doped CS exhibits a more suitable degradation rate and enhanced bioactivity, presenting significant application prospects in the field of bone defect repair.