Studies On Structure And Properties Of Chemical Cross-linked Silk Fibroin Gel

With the development of biological technology, biomedical materials exhibit great developing potential and board application foreground. Silk fibroin(SF) is a natural macromolecule. Based on the unique advantages of SF such as biocompatibility, good oxygen and water vapor permeability and biodegradability, it has been applied for biomaterials such as enzyme-immobilization, drug carrier, antithrombogenic materials, wound dressing and cell culture substrate. However, the varieties and forms of fibroin materials prepared currently were too single, what's more, the mechanic properties of fibroin materials made by normal methods cannot meet utility demands.In order to explore the method of fibroin materials with higher flexibility applying to biomaterials, we studied the structure and formation mechanism of cross-linked fibroin gel (CFG), which was prepared by chemical reaction between silk fibroin solution and epoxide Polyethylene Glycol Diglycidyl Ether (PGDE), and preparation conditions, as well as some properties were also discussed. The results indicated that CFG with higher flexibility could be made by the reaction between silk fibroin solution and epoxide cross-linker. FT-IR spectrum of CFG showed that a strong absorption appeared at 1104.7cm^-1 was due to PGDE induced onto silk fibroin chains by opening the ring ethers on both side. DSC curve indicated that the thermal decomposed temperature of CFG appeared at 299.37℃, higher than FG, which was at 295.14℃. This result suggested that more stable structure was formed and CFG had better thermal stability. The ¹³C NMR spectrum of CFG showed that a downfield shift of the aromatic protons of the tyrosine residue from the corresponding protons of silk fibroin, confirmed the presence of cross-linking structure, and pointed out the interaction between fibroin and PGDE could reject the intra-reaction in fibroin molecules, resulting the decline ofβ-sheet component and increment of random coin structure, Amino acid analysis farther showed the cross-linking reaction sites were mainly on phenolic hydroxyl group of the tyrosine residue, theε-amino group of lysine residue and imidazole group of the histidune residue, basing on which we drew the reaction pattern and calculate the necessary dose. X-ray diffraction explained the stereo structure change of CFG was due to disordering the molecular orientation by PGDE bonding to silk fibroin. Secondly, we studied CFG preparation conditions, and concluded such factors as PGDE%, SFwt%, NaCl% and reaction temperature could make influence on the formation of cross-linking structure. These factors affected not only the inter-molecules cross-linking between fibroins and PGDE, but also the intra-molecules cross-linking between fibroins, lastly, we measured some basic properties of CFG. The results of mechanic measurement showed that CFG had super compress strength and flexibility, and the compress distortion could reach up to 79% when at adequate PGDE additions(2-5%), while the compression declined at higher PGDE contents(8-20%), due to steric effect caused by PGDE. the solubility of CFG in acid, alkali, as well as salt solution, was decreased compared with pure fibroin gel (FG), suggesting the increasing stability.All the studies results indicate the feasibility of preparing silk fibroin materials with higher flexibility by chemical cross-linking. The conclution provides a new way for the preparation methods of fibroin materials, and the structure analysis methods will give a meaningful reference for related studies of fibroin materials with cross-linking structure.