Study On The Effects Of Silk-based Functional Scaffold For Spinal Cord Injury Repair

Biomaterials are the hotspot in the field of tissue engineering,and silk fibroin are widely favored due to their unique hierarchical structure and biocompatibility.Although a series of gratifying progresses have been made in tissue-engineered nerve grafts,there are still challenges such as insufficient bioactive cues,lack of targeting sites and effective stimulation signals for nerve tissue regeneration.Therefore,there is still a long way to find practical and effective approaches to design and prepare an artificial spinal cord with multiple stimulation signals in spinal cord repair.On the basis of deeply understanding of the structure and components of the natural spinal cord,this project is based on the principle of bionics to create a favorable microenvironment that promotes spinal cord repair.Firstly,silk fibroin nanofibers（SNF）were prepared in large quantities from waste silk as raw material,and oriented-channels scaffolds were prepared by combining SNF with directional freeze-drying technology.We systematically studied the morphology,structure,physical and chemical properties of SNF and directional porous structure.The results show that the hierarchical structure of silk can be effectively deconstructed by physical-chemical interactions,and micro and nano-scale fibrils of silk are obtained.By using conventional chemical cross-linking technology,hyaluronic acid（HA）can be coated on the surface of SNF.The pore size,porosity,connectivity and hydrophilicity of the scaffold can be controlled by adjusting the HA concentration;when the HA concentration reaches 20wt%,the contact angle of the scaffold at 0.007 s is 0°,and the material can be completely wetted.With the increase of freezing temperature,the pore size of the material increases gradually.The diameter of the pores formed at-196 ℃ is about 10 μm-30 μm,while the diameter of the pores formed at-80 ℃ increased to 80 μm-120 μm.In order to further improve biological activity of the scaffold,basic fibroblast growth factor（b FGF）was grafted on the surface of the scaffold by chemical bonding.The results showed that b FGF was successfully introduced into the scaffold.X-ray spectroscopy（XPS）data showed that b FGF and the-COOH on the surface of the scaffold is bound by an amide bond.Secondly,to further evaluate the in vitro biocompatibility of the modified scaffolds,mouse embryonic stem cells and human umbilical vein endothelial cells were seeded on the scaffolds.Seven days after seeding,the results of CCK8 showed that the cell viability in the modified scaffold was higher than that of the other two groups.The results suggested that the scaffolds before and after modification could support cell adhesion and migration,especially the scaffolds with directional pore structure had a significant guiding effect on the direction of cell migration;while the surface-modified scaffolds had significant effects on cell growth and migration enhancement.Finally,the role of scaffolds in the repair of spinal cord injury was explored in an animal model of SD rat spinal cord transection.The stents were implanted into the spinal cord transection lesions of the rats,and the motor function recovery of the rats was observed within70 days after operation.The results show that the silk-based functional scaffolds can significantly promote the repair of spinal cord injury,and the surface-modified scaffolds can significantly improve the recovery of neurons in the rat model of spinal cord injury,improve their survival rate,and promote part of the motor function recovery.This study provides a potential new material for the treatment of spinal cord injury,further enriches the theory of nerve tissue regeneration,and has important effect on theoretical research and practical application prospects.