Enhancing bioactivity and mechanical performances of hydroxyapatite–calcium sulfate bone cements for bone repair: in vivo histological evaluation in rabbit femurs

Abstract

This study deals with synthesizing hydroxyapatite–calcium sulfate bone cements or HAP–xCaS for bone repair. The effect of CaS on the setting time, injectability, washout resistance, phase evolution, water absorption, and physical, microstructural, and mechanical properties, as well as in vitro apatite-forming ability test and pH behavior of the HAP were investigated. Implantation of bone cement in rabbit femur and in vivo histological analysis were also analyzed. Initial and final setting times decrease with increasing CaS, which would be helpful for clinical procedures. All compositions have mixed phases of HAP, CaS, brushite, and gypsum. The prepared bone cement exhibited a dense structure and increased linear shrinkage with increasing CaS content. Adding more CaS inhibited grain growth and improved the mechanical properties, including compressive strength (σ_c), bending strength (σ_f), and Young's modulus (E). SEM micrographs displayed that the x = 0.7 or HAP–0.7CaS bone cement produced the highest ability to induce in vitro apatite formation, indicating its biocompatibility. In vivo histological analysis for the HAP–0.7CaS bone cement demonstrated that more new bone formed around defects and bone cement particles. Osteoblasts were found peripherally at the bone trabeculae, and occasional osteoblast-like cells were observed at the granules after 4–8 weeks of implantation. The obtained results indicated that the HAP–0.7CaS bone cement has the potential to exhibit good bioactivity, injectability, and good mechanical properties for bone repair applications.