Study On Modification Of Regenerated Silk Fibroin Fibers With Photosensitive Nanomaterials

Silk fibroin is widely used in human tissue engineering,biomedicine,optical devices and other fields because of its good biocompatibility and degradability.In order to broaden the application range of regenerated silk fibroin(RSF)materials and prepare multi-functional and high value-added silk fibroin materials,functional nano-materials were added into silk fibroin materials by wet spinning.Tungsten oxide nanoparticles(WO₃NPs)and cesium tungsten bronze nanoparticles(Cs_xWO₃NPs)are excellent photosensitive materials,which can endow RSF fibers with a variety of functions and improve their mechanical properties.These functional silk fibroin materials are not only meaningful for the development and application of solar energy,but also have potential applications in military,energy resources,medicine and other fields.In this study,nano-tungsten oxide and nano-cesium tungsten bronze were used to modify RSF fiber.The mechanical properties,structure and optical properties of modified RSF fiber were measured,and the effect of nanoparticles on the structure of silk fibroin solution was studied.1.A series of photochromic RSF/WO₃NPs hybrid fibers with different mass fractions by wet spinning have been prepared.The effects of WO₃NPs with different mass fractions on the morphology,mechanical properties,secondary structure,crystal structure,thermal stability and photochromic properties of RSF fibers were studied.The results of scanning electron microscopy(SEM)showed that WO₃NPs with different mass fractions had no significant effect on the morphology and diameter of RSF fibers.The results of Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)showed that 4wt%-RSF/WO₃NPs hybrid fibers had the lowest?-sheet content,and its crystallinity and crystallite size were smaller than RSF fibers.However,the number of crystals per unit volume was higher than that RSF fibers,which was about 1.34 times that of RSF fiber.The mechanical test results showed that the mechanical properties of 4wt%RSF/WO₃NPs hybrid fibers(breaking strength was214.52±16.00 MPa,break strain was 97.82±17.50%,breaking energy was 129.14±25.56MJ/m³)are significantly improved compared with RSF fibers(breaking strength was150.07±18.46 MPa,break strain was 53.19±16.47%,breaking energy was 58.19±20.22MJ/m³).Thermogravimetric Analysis(TGA)demonstrated that 4 wt%-RSF/WO₃NPs hybrid fibers had better thermal stability than RSF fibers.The photostability test showed that the hybrid fibers color can rapidly change within 5 s under the ultraviolet light and also can change within 1 min under the sunlight.The fibers still retained good photochromic ability after more than after 20 tests of the treatment.2.RSF/Cs_xWO₃NPs hybrid fibers with different mass fractions were prepared by wet spinning with Cs_xWO₃NPs as the blend to modify the mechanical and photothermal properties of RSF fibers.The SEM results showed that compared with WO₃NPs(2-5 nm),Cs_xWO₃NPs with larger particle size also had no significant effect on the morphology and diameter of RSF fibers.FT-IR and XRD results showed that the addition of Cs_xWO₃NPs reduced the?-sheet content,crystallinity and crystallite size of the hybrid fibers,but the number of crystals per unit volume was higher than that of RSF fiber,which was about 1.27 times of RSF fibers.The highest breaking stress,breaking strain and breaking energy of the 3 wt%-RSF/Cs_xWO₃NPs hybrid fibers can be reached 233.41±19.45 MPa,119.63±12.59%and 171.21±17.17 MJ/m³.Thermogravimetric Analysis(TGA)showed that 3 wt%-RSF/Cs_xWO₃NP hybrid fibers had better thermal stability than RSF fibers.The light test results showed that the temperature of RSF/Cs_xWO₃NP hybrid fiber and RSF fiber increased more rapidly than that of RSF fiber at the same light time.The average temperature of RSF/Cs_xWO₃NP hybrid fibers reached52.2°C in 1 min and 76.7°C in 10 min,respectively.3.The effects of WO₃NPs with different mass fractions in different incubation time solutions on the self-assembly behavior of silk fibroin were studied by Th T fluorescence spectroscopy(FL)and Fourier transform infrared spectroscopy(FT-IR).The FL showed that the fluorescence intensity of 4 wt%-RSF/WO₃NPs solution was the lowest,indicating that the?-sheet content was the lowest.With the increase of WO₃NPs content,the?-sheet content showed a trend of recovery,but it was still lower than that in the RSF solution.Moreover,a large number of?-sheet structures were formed during the incubation period from 8 h to 12h,indicating that WO₃NPs had begun to affect the structural changes of silk fibroin in the solution state,hindering the movement and recombination of RSF molecular chains,resulting in the decrease of?-sheet content.The results of FT-IR were consistent with those of fluorescence spectra.The?-sheet content of freeze-dried 4 wt%-RSF/WO₃NPs was the lowest,but its?-sheet content was higher than that of 4 wt%-RSF/WO₃NPs hybrid fibers.This was attributed to the conformational change of fibroin protein in 4 wt%-RSF/WO₃NPs solution during freeze-drying,resulting in the increase of?-sheet content in freeze-dried RSF/WO₃NPs.