| Bone repair material is one of the most important fields in biomedical materials. The main function of bone repair material is to repair the tissue defects and recover the physiological function of bone. The ideal bone repair material should have the characteristics such as good biocompatibility, appropriate mechanical properties, good biodegradability and processibility. Poly (ε-caprolactone) (PCL) is a type of biodegradable polymer with good biocompatibility. However, the lower mechanical properties restrict its application in bone repair field. Silk fibroin fiber (SF) is a kind of natural fiber based on polypeptide, which has good elasticity and good biocompatibility. Therefore, biocomposite fabricated with PCL and SF would have more promising foreground in bone repairing applications.Firstly, the effects of fiber content and irradiation treatment on structure and properties of silk fibroin fiber reinforced PCL (SF/PCL) biocomposite were investigated. The results show that the tensile strength, flexural strength and modulus of PCL are obviously reinforced by the addition of SF. The maximum tensile and flexural strengths appear at the fiber contents of 35% and 45%, respectively. In the dose range of 0-300kGy, SF/PCL biocomposite exhibits maximum strength and modulus at the dose of 150KGy. For SF/PCL biocomposite, the glass transition temperature (Tg) of PCL component increases with the irradiation dose. During irradiation, both PCL and SF can produce free radicals. Some transformations or reactions of radicals may take place and enhance the interfacial interaction between SF and PCL matrix.Secondly, porous PCL and SF/PCL biocomposite scaffolds were successfully fabricated based on the design principle of tissue engineering. The resulting scaffolds have an interconnected porous structure with both macropores (150μm-300μm) and micropores (several micrometers). The porosity of scaffolds can be controlled from 40% to 91%. SF improves the compressive strength and the hydrophilicity of PCL scaffold. For the PCL scaffold with 65% porosity, the compressive strength is enhanced by 55% and the water contact angle drops from 108o to 64o at the fiber content of 35%. Remarkably, the SF/PCL scaffolds still possess good thermal processibility. The further evaluations on biocompatibility and biological safety of PCL and SF/PCL biocomposite were performed by cytotoxicity test, acute systemic toxicity test, hemolysis test, pyrogen test and skin hypersusceptibility test. The results indicate that there are no obvious morphological changes of canine bone marrow mesenchymal stem cells (BMSCs) on both PCL and SF/PCL biocomposite. There are no acute systemic toxicity,no hemolytic reaction and no skin hypersusceptibility. Furthermore, BMSCs can attach to the porous SF/PCL biocomposite scaffold and proliferate well in the scaffold.The degradation rate of SF/PCL biocomposite scaffold in vitro is quicker than that of bulk materials, and the degradation rate in vivo is quicker than that in vitro. The presence of SF can ease the relatively high acidity which is caused by the process of PCL degradation to some extent. Therefore, after being embedded in vivo, SF/PCL biocomposite can introduce less inflammatory response compared with pure PCL.On the basis of above researches, we fabricated a novel kind of biodegradable internal fixation device based on SF/PCL biocomposite for the first time. The device was utilized for repairing rib fracture and had the advantages of minimal surgical trauma and short operation time. In the experiment of repairing canine rib fracture, good trend of healing in fracture sites could be detected after 15 days'implantation. The fracture sites could get complete healing after 6 months. All the research results above can provide the theoretical and experimental evidences for the further applications of SF/PCL biocomposite in bone repairing field.
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