In situ silk fibroin-mediated crystal formation of octacalcium phosphate and its application in bone repair

The development of an ideal scaffold material is critical for the repair of bone defects. Being an important precursor of the mineralized matrix of bone tissue, octacalcium phosphate (OCP) has been considered a promising bone substitute. However, its application is largely limited due to the thermodynamical instability and poor processability of it. In this study, OCP was prepared by co-precipitation in the presence of small amount of silk fibroin (SF), which regulated the crystallization of OCP and led to the formation of SF-OCP complex. The diameters of OCP crystals in OCP, 0.1SF-OCP, 0.3SF-OCP and 1SF-OCP complexes were 489.0 ± 399.1 nm, 102.2 ± 50.7 nm, 94.7 ± 48.4 nm and 223.7 ± 167.6 nm, respectively. However, the shape of OCP crystals did not apparently change by the presence of SF. Further, porous SF/OCP composite scaffolds with pore size of 111.9 ± 33.1 μm were prepared, in which small crystals of SF-OCP complex were embedded in a SF matrix. MC3T3-E1 cells could attach and proliferate well on both the rugged surfaces and the pores of SF/OCP scaffolds, indicating their decent biocompatibility. Further, SF/OCP scaffolds markedly promoted bone regeneration in a rat calvarial critical-sized defect model. Both micro-CT and H&E characterizations showed that bone formation not only occurred around the scaffolds, but also penetrated into their center. Therefore, such SF/OCP composite scaffolds may have potential applications in bone tissue engineering.