Preparation And Properties Of Photocrosslinked Silk Fibroin/Gelatin Copolymerized Hydrogels

Hydrogels are widely used as scaffold materials in tissue engineering due to their advantages in structure and characteristics similar to natural tissues and adjustable performance.Silk fibroin is widely used in the preparation of hydrogels due to its massive advantages such as excellent mechanical properties,good biocompatibility and biodegradability.However,the current preparation methods have some limitations such as the preparation conditions are not mild enough,the sol-gel transformation is too slow,or strength of the hydrogel is high enough but the flexibility and extensibility are insufficient.Here,we prepared copolymerized hydrogels of silk fibroin and gelatin using the method of ultraviolet(UV)light-driven cross-linking.In this method,in the presence of ultraviolet light and photoinitiator,the vinyl-modified silk fibroin and gelatin co-mixed solution can achieve sol-gel transition within 60 s,and the resulting copolymerized hydrogels not only have the characteristics of good flexibility and extensibility,but also have the advantages of adjustable performance and integration of multiple biological functions.The specific research contents are as follows:(1)The silk fibroin molecules and gelatin molecules were modified to endow them ultraviolet light activity.Firstly,the vinyl modification of silk fibroin molecules was carried out by using monomer glycidyl methacrylate(GMA).The effect of modification monomer concentration on the degree of vinyl modification on silk fibroin molecules was explored by controlling the amount of GMA used.The vinyl groups can be successfully modified on the silk fibroin molecule under the current experimental conditions which was confirmed by the measurement and analysis of the Fourier-transform infrared(FT-IR)spectrum and proton nuclear magnetic resonance(~1H-NMR)spectrum of silk fibroin before and after modification.Quantitative calculation results of ~1H-NMR spectrum reveal that the modification degree of vinyl groups on silk fibroin molecules showed a trend of increasing first and then decreasing,and the modification degree can reach 37.7%when GMA concentration was 453 mM.In addition,vinyl-modified silk fibroin molecules still exhibit the ability to form?-sheets under ethanol induction.Furthermore,the gelatin molecules were modified by using monomer methacrylic anhydride(MA).the successful modification of vinyl groups on the gelatin molecules was confirmed by measurement and analysis of FT-IR spectrum and ~1H-NMR spectrum of the gelatin before and after modification.The quantitative calculation of ~1H-NMR spectrum shows that the modification degree of the vinyl groups on the gelatin molecules can reach 79%under the current experimental conditions.(2)On the basis of the previous part research,the vinyl-modified silk fibroin(RSFMA)and vinyl-modified gelatin(GelMA)were combined to prepare copolymerized hydrogels by UV light-driven cross-linking.We measured the time of the co-mixed solution transformed into hydrogels.The results show that the co-mixed solution can transform into hydrogel after UV exposure for 60 s.We determined the degree of vinyl groups cross-linking and the molecular conformation of RSFMA in the copolymerized hydrogel network by analysis and quantitative calculation of FT-IR spectrum and ~1H-NMR spectrum.The results reveal that vinyl groups were involved in cross-linking,the cross-linking degree can reach 86%,and silk fibroin molecules did not undergo the transition of?-sheet structure.By adjusting the ratio of silk fibroin and gelatin,we explored the effect of silk fibroin content on the internal microstructure,swelling degree and in vitro degradation performance of the copolymerized hydrogels.The results show that the internal pore diameter and swelling degree of the copolymer hydrogels gradually increases,but the degradation rate in vitro become slower with the silk fibroin content increased.In the macro-evaluation of mechanical properties,copolymerized hydrogel with 15 w/v%concentration and ratio of silk fibroin/gelatin 6:2 can withstand crimping,twisting and knotting,indicating that the copolymerized hydrogels have good flexibility.The strain of the copolymerized hydrogels can reach42.8%of its original length during stretching,indicating that the hydrogels have proper extensibility.During the compression test,the copolymerized hydrogels could withstand 200 g load,and could be return to the original state after the load was removed,indicating that the copolymer hydrogels have the ability to withstand compression and have good resilience.(3)Finally,the possibility of application of copolymerized hydrogels in three aspects was preliminarily explored.Firstly,we evaluated the possibility of copolymerized hydrogels as drug-loaded scaffolds for drug release.The experimental result of antibiotic vitro release performance of the copolymerized hydrogels reveals that ampicillin can reach Maximum release after about 10 h.In addition,the feasibility of copolymerized hydrogel as an injectable in-situ hydrogel platform was explored.The precursor solution was injected into the glass surface to form an English pattern,and then the precursor solution was cured by UV-light driven,thereby evaluating the ability of the co-mixed solution to form hydrogel in situ.And the precursor solution was injected into holes with different shapes to evaluate its ability to fill irregular cavities.The results show that this method can form hydrogels in situ and has good cavities filling properties.Lastly,we put forward the idea of material preparation by rapid prototyping and post-processing.Through this method,the design,fixation and strengthening of various shapes of copolymer hydrogels were realized,indicating that the shape of copolymer hydrogels can be customized under this method.The physical and mechanical properties can be greatly enhanced,thereby it is expected to be used in the design of tissue engineering scaffolds and the construction of protein devices.