Mechanical reinforcement of injectable calcium phosphate cement/silk fibroin (SF) composite by mineralized SF

Calcium phosphate cements (CPCs) are promising injectable orthopedic materials with excellent biocompatibility and osteoconductivity. However, the inferior mechanical strength limits their use to low load-bearing areas only. In this study, we synthesized hydroxyapatite (HA)-silk fibroin (SF) complex through a co-precipitation method and supplemented it to an injectable CPC/SF composite. We found that the compressive strength of the three-component composite, CPC/HA-SF/SF, kept increasing with HA-SF content if it did not exceed 3 wt%. Such a reinforcing effect was likely the result of improved interfacial integrity and oriented growth of HA crystals in CPC/SF composite upon HA-SF supplementation. The setting time of CPC/HA-SF/SF composites decreased as a function of HA-SF content, with no apparent effect on injectability. Moreover, the CPC/HA-SF/SF composites showed good biocompatibility both in vitro and in vivo. Such composites hold good promise for many orthopedic applications, including serving as filler materials for minimally invasive surgeries to treat vertebral fractures.