Functional Self-assembly Peptide/Silk Fibroin Complex Nanohydrogel Promotes Neural Regeneration After Spinal Cord Injury

Objective: There will be an inhibitory microenvironment in the injury site after spinal cord injury(SCI),such as intense local inflammatory response,insufficient secretion of neurotrophic factors,lack of neurons,and the formation of glial scar and voids,which seriously hinder nerve regeneration and functional recovery.In recent years,the concept of tissue engineering has attracted extensive attention in the field of neural repair and regeneration.The reconstruction of nerve regeneration microenvironment in spinal cord injury with biomaterials can promote nerve regeneration and function recovery more effectively than traditional treatment.Based on the study of functional self-assembly peptide RADA16-IKVAV(F-SAP),in order to improve its physicochemical properties,a composite nanohydrogel was prepared by synergistic assembly with silk fibroin(SF),which was implanted in vivo for long-term treatment of SCI,to explore its effects on axonal regeneration and functional recovery.Method:(1)Material performance characterization: F-SAP and SF were combined to prepare F-SAP/SF composite nanohydrogels,which were subjected to various characterization methods,such as rheology,AFM,SEM,CD,FTIR,Raman,etc.on its mechanical properties,morphology,and secondary structure.In addition,we used the Elisa kit to verify its ability of slow-releasing growth factors in vitro;(2)in vivo experiments: the T9 segment was completely excised with 2 mm laminectomy.After treatment,they were divided into three groups: 1)F-SAP/SF group;2)F-SAP group;3)SCI group(no intervention).On the 14 th day after the operation,the inflammation response and axon regeneration of the injured microenvironment were detected by immunofluorescence staining,Western blot and Q-PCR.On the 60 th day after the operation,the myelin sheath and CST regeneration of the injured area were detected by immunofluorescence staining,TEM and BDA tracing CST.The CMEP and BBB scores were used to detect the effect of the functional recovery of the hindlimb.Result:(1)Compared with F-SAP hydrogel,F-SAP/SF hydrogel has excellentmechanical properties and more complicated secondary structure.After assembling,more dense microscopic morphology can be observed,and can better coat and release active factors.(2)The implantation of F-SAP/SF hydrogel can significantly reduce local inflammatory response,and improve axonal regeneration and remyelination in injured area,and effectively promote the regeneration of CST across the injured area,and ultimately achieve the effect of promoting motor function recovery.Conclusion: A modified hydrogels with better mechanical properties can be prepared by compound modification of F-SAP and SF,which can slow release growth factors,and can be used in SCI rats.It can regulate local inflammatory response,improve the inhibitory microenvironment,bridge the broken edge of spinal cord,support axonal regeneration,and promote function recovery.