Preparation,Structure And Performance Of Silk Fibroin Nanofibers And Its Applications In Biomedical Field

Silk nanofibers as elements are critical to design bioactive materials with specific structure and function in biomedical field.Silk nanofibers with high crystal contents have showed promising prospects as injectable drug carriers,anisotropic hydrogels,and hierarchical porous sponges.However,high beta-sheet content endows the nanofibers hydrophobic capacity and stability,resulting in the loss of conformational tenability and solution state at higher concentration of above 0.5%.These problems lead to limited control of drug release behaviors and also inadaptability of designing silk-based biomaterials.Here,injectable drug carrier was developed by combing silk nanofiber hydrogels?SF-gel?and calcium carbonate microspheres.The carriers showed programmable release behaviors without the sacrifice of injectability of the silk nanofiber hydrogels.Optimized anti-tumor capacity was achieved through adjusting the release behaviors.Then,amorphous silk fibroin nanofibers were prepared to satisfy various requirements of tissue engineering.By regulating the ratio of lithium bromide and formic acid,silk fibroin nanofiber solution systems with amorphous structures were successfully prepared?SF-FA?.The solvent systems partly destroy intermolecular hydrogen-bonds to remain nanofiber structures of native silk fibers.The aqueous solutions were composed of silk nanofibers with diameters of 10-20 nm and lengths of 200-350 nm.The concentration of SF-FA can reach to 8%without gel formation,meeting the requirements of further fabrication of bioactive silk fibroin materials.The nanofiber solution can be stored at 4^o C for one week and can also be freeze-dried and stored for more than two months without gel formation and conformational transition into beta-sheet.These results suggested that SF-FA is suitable element for the preparation of various biological materials.Porous sponge scaffolds and films were subsequently prepared using SF-FA as element and showed different morphology,conformational composition and mechanical properties when compared to that derived from traditional silk fibroin solutions.The secondary structures and mechanical properties of the sponges and films can be further tuned through methanol,ethanol or water vapor treatments.Meanwhile,amorphous nanofibers significantly improved the spinnability of silk protein electrospinning and the controllability of hydrogel formation.Compared with original electrospinning process,the electrospun nanofibers were successfully prepared at lower concentration in aqueous solution.Silk hydrogles with higher mechanical property were also achieved via same gelation process..In summary,two different strategies were used to solve inherent problems of silk nanofibers?SF-gel?with high crystal content.Improved drug release behavior was optimized by introducing other materials while amorphous silk protein nanofibers?SF-gel?were obtained through tuning silk protein dissolution process and used to develop silk biomaterials with different structures and functions.We believe that our study provides better substrates to design bioactive materials with specific functions in the future.