Study On Modification Of Regenerated Silk Fibroin Fibers With Gold,Silver And Titanium Dioxide Nanomaterials

Natural silk has excellent cell compatibility,biodegradability,and is non-toxic and harmless to human body and tissues.It has been used in the field of new materials such as tissue engineering,biomedicine.Wet spinning is a simple,low cost,and environmentally friendly spinning method.It can make natural silk become silk fibroin solution,and different materials can be added to make RSF fibers with different functions,which can increase its value,but the RSF fibers made by wet spinning has low breaking strength and breaking strain.The mechanical properties are not as good as natural silk.Therefore,improving the mechanical properties of RSF fibers has become an important research topic in the field of silk fibroin biomaterials.The feeding of gold nanoparticles（Au NPs）,silver nanoparticles（AgNPs）,titanium dioxide nanoparticles（Ti O2NPs）and other nanomaterials to silkworms have a significant effect on the improvement of silk mechanical properties.The size and morphology of nanomaterials can significantly affect their properties.In this paper,gold,silver and titanium dioxide nanomaterials are used to modify the wet-spun RSF fibers,and three blending systems are used to systematically study the effect of nanomaterials on the mechanical properties and structure of wet-spun RSF fibers.They are silver nanoparticles（AgNPs）with different sizes;different nanoclusters with the size of 2～4 nm（gold nanoclusters（Au NCs）,silver nanoclusters（Ag NCs）and titanium dioxide nanoclusters（Ti O2NCs））and silver nanomaterials with different shapes（silver nanowires（Ag NWs）and Ag NCs）.The main results are as follows:1.Effect of AgNPs size on the structure and properties of RSF fibers Four AgNPs with particle sizes of 2.8±1.5 nm,19.1±2.4 nm,37.5±3.1 nm and 58.1±3.8 nm were synthesized by one-pot synthesis method（recorded as 2 nm,19 nm,37 nm and58 nm）,and were blended with silk fibroin solution to modify the RSF fibers by wet spinning,respectively.The effects of the content of AgNPs on the morphology,mechanical properties and structure of RSF fibers were studied.The effects of AgNPs size on the mechanical properties of RSF fibers were also studied.Scanning electron microscopy（SEM）results showed that AgNPs with different sizes had no significant effect on the morphology and diameter of RSF fibers.Synchrotron radiation micro infrared spectroscopy（FTIR）and wide-angle X-ray diffraction spectroscopy（WAXD）results showed that AgNPs with different sizes had no significant change in the secondary structure（α-helix/random coil,β-sheet,β-turn）and crystal structure of RSF fibers,but they can increase theβ-sheet and crystallinity,and reduce grain volume.Moreover,the smaller AgNPs,the more beneficial it is to increase theβ-sheet and crystallinity of the fibers and reduce the volume of the crystal grains.Mechanical test results showed that AgNPs with different sizes can significantly improve the mechanical properties of RSF fibers compared with the blank group（breaking strength was 158.13±9.27MPa,breaking strain was 15.02±8.67%）.When the content of 2 nm,19 nm,37 nm,58 nm AgNPs were 2 wt‰,0.4 wt‰,4 wt‰,8 wt‰,the mechanical properties of the fibers were the best,breaking strength and breaking strain were 294.34±19.12 MPa,135.95±21.64%;274.32±25.32 MPa,124.28±19.05%;243.32±15.91 MPa,93.23±12.58%;207.09±18.54MPa,70.51±20.49%,respectively,RSF fibers with smaller AgNPs have better the mechanical properties.2.Effect of nanoclusters on the structure and properties of RSF fibers 2.3±1.1 nm Au NCs and 4.2±1.4 nm Ti O2NCs were synthesized by one-pot synthesis method,they were blended with silk fibroin solution respectively.Compared with Ag NCs,the effects of different nanoclusters on the morphology,mechanical properties and structure of RSF fibers were studied.SEM results showed that Au NCs and Ti O2NCs had no significant effect on the morphology and diameter of RSF fibers.FTIR and WAXD results showed that Au NCs and Ti O₂NCs can improve theβ-sheet and crystallinity of the fibers,and reduce the grain volume.The mechanical test results showed that compared with the blank group（breaking strength was 158.13±9.27 MPa,breaking strain was 15.02±8.67%）,both Au NCs and Ti O2NCs have obvious enhancement effect on the mechanical properties of RSF fibers.When the content of Au NCs,Ti O₂NCs were 0.8 wt‰,0.4 wt‰,the mechanical properties of RSF fibers were the best,and the breaking strength and breaking strain were 260.67±15.18MPa,104.62±11.28%;249.52±16.29 MPa,112.2±14.01%,respectively.Compared with RSF fiber with 2 wt‰Ag NCs（breaking strength was 294.34±19.12 MPa,breaking strain was 135.95±21.64%）,the effect of three nanoclusters on the mechanical properties of RSF fibers was:Ag NCs>Au NCs>Ti O2NCs.3.Effect of silver nanomaterials on the structure and properties of RSF fibers Silver nanowires（Ag NWs）with the diameter of 80-100 nm and the length of 8-11μm were synthesized by one-pot synthesis method and were blended with silk fibroin solution to modify the RSF fibers.Compared with Ag NCs,the effects of silver nanomaterials on the morphology,mechanical properties and structure of RSF fibers were studied.SEM results showed that Ag NWs had no significant effect on the morphology and diameter of fibers.FTIR and WAXD results showed that RSF fibers with Ag NWs had higherβ-sheet and crystallinity,and smaller grain volume.The mechanical test results showed that RSF fibers with Ag NWs had better mechanical properties than the blank group.When the content of Ag NWs was 4wt‰,the mechanical properties of the RSF fibers were the best,and the breaking strength and breaking strain were 233.41±19.45 MPa and 88.37±9.06%,respectively.Compared with RSF fibers with 2 wt‰Ag NCs（breaking strength was 294.34±19.12 MPa,breaking strain was 135.95±21.64%）,RSF fibers with 4 wt‰Ag NWs had worse modification effect on the mechanical properties of RSF fibers.