Effect Of CeO₂ And CeO₂@SiO₂ NPs On Regenerated Silk Fibroin（RSF） Against UV-aging

As a new generation of biodegradable natural polymer materials,silk fibroin（SF）has excellent biocompatibility,biosafety,excellent mechanical properties,and modifiability.it is suitable to be developed as a functional regenerated silk fibroin（RSF）material with high added value.However,under the synergistic effect of outdoor ultraviolet light,oxygen and water molecules,RSF materials are prone to aging such as embrittlement and yellowing,which seriously affects the service life and application effect of RSF materials.In this paper,RSF fibers and solutions were used as the main research objects.Cerium dioxide nanoparticles（CeO₂ NPs）and cerium dioxide@silica nanospheres（CeO₂@SiO₂ NPs）were used to alleviate the problems of mechanical properties degradation and service life shortening caused by aging of RSF fibers.The antibacterial properties,thermal stability and photooxidation resistance of RSF/CeO₂@SiO₂ NPs hybrid fibers were studied,which expanded the application range of hybrid fibers.The main research contents are as follows:1.The use of CeO₂ NPs to modify RSF effectively improves the UV aging resistance of hybrid fibers.RSF/CeO₂ NPs hybrid fibers with different concentration gradients were prepared by wet spinning,and the aging degree was measured by the mechanical properties and morphological changes of the hybrid fibers.The results showed that when the addition amount was 2.0 wt%,the RSF/CeO₂ NPs hybrid fiber had the highest content ofβ-sheet structure and the best mechanical properties.The breaking strength was 215.59±5.20 MPa and the elongation at break was 126.94±4.26%,which were close to 2 times of the control group.After 28 days of artificial ultraviolet aging test,the breaking strength（40.54±8.36 MPa）and elongation at break（32.13±4.68%）of the blank RSF fiber decreased by 63.96%and32.21%,respectively.However,the breaking strength（171.01±3.58 MPa）and elongation at break（102.02±6.35%）of RSF/CeO₂ NPs hybrid fibers only decreased by 23.21%and 19.26%,respectively,and the mechanical properties remained good.At the same time,the decrease ofβ-sheet was 3.36%lower than that of the blank group.The results show that the stability of RSF/CeO₂ NPs hybrid fibers is higher and the mechanical properties decrease more slowly under the same aging time.By studying liquid silk fibroin,it was found that CeO₂ NPs can prevent the disorder of silk fibroin structure,reduce the cleavage of disulfide bonds,and improve the stability of silk fibroin molecules.2.The CeO₂@SiO₂ NPs with good dispersion were prepared,and the role of nanomaterials in the UV aging process of RSF fibers was studied.RSF/CeO₂@SiO₂NPs hybrid fibers were prepared by wet spinning.After 56 days of artificial ultraviolet aging,the mechanical properties and morphology of the hybrid fibers were tested,and the ultraviolet aging mechanism of RSF was studied.Experimental results show that CeO₂@SiO₂ NPs improved the mechanical properties of regenerated silk fibers.When the content of CeO₂@SiO₂ NPs reached 4 wt%,the mechanical properties of RSF/CeO₂@SiO₂ NPs hybrid fibers reached the best,and theβ-sheet content of hybrid fibers was the highest.After 56 days of UV aging,its breaking strength（167.27±2.75 MPa）and elongation at break（101.14±5.66%）remained good.After aging for 28 days,the mechanical properties of RSF/CeO₂@SiO₂ NPs hybrid fibers remained higher and the internal structure was denser.It shows that the modifier CeO₂@SiO₂ NPs has better anti-ultraviolet aging performance than CeO₂NPs.Based on circular dichroism,SDS-PAGE,Zeta potential analysis and fluorescence inverted microscope,the changes of silk fibroin in solution were observed.It was found that CeO₂@SiO₂ NPs played a role in stabilizing silk fibroin molecules and reducing denaturation under ultraviolet conditions.3.The stability and oxidation resistance of RSF/CeO₂@SiO₂ NPs hybrid fibers were investigated to broaden their application fields.The stability of RSF/CeO₂@SiO₂ NPs hybrid fiber was studied by differential scanning calorimetry,thermogravimetric analysis,bacteriostatic experiment,biodegradability and alkali resistance sweat test.The free radical scavenging experiments of the hybrid fibers were carried out to explore their antioxidant properties.The experimental results show that the RSF/CeO₂@SiO₂ NPs hybrid fiber has a more stable crystal structure than the RSF fiber,which makes it more stable in high temperature,enzyme environment and slightly alkaline environment.In addition,RSF/CeO₂@SiO₂ NPs hybrid fibers have the ability to inhibit Staphylococcus aureus and anti-oxidation,which is conducive to its application in medical fields such as surgical sutures.