Abstract: The structure of cross-linked fibroin gel(CFG) prepared by the reaction of cross-linking (agent) epoxide polyethylene glycol diglycidyl ether(PGDE) with silk fibroin solution was investigated. The results indicate that CFG express the whole homogeneous morphological structure observed by site microscopy phase contrast, while the pure fibroin gel(FG), which hadn't been cross-linked with PGDE, showed the particle-piled structure. There was an absorption peak of alkyl ether in PGDE appearing at 1 104 cm^-1 of the FTIR spectrum of CFG, while it didn't show the characteristic peak of epoxide in both sides of PGDE. It revealed that PGDE has been cross-linked with silk fibroin by opening the rings. The amino acid analysis of CFG can be used to explain that the content of tyrosine, histidine and lysine obviously decreased after the reaction, and PGDE cross-linking occured at these sites. The chemical shift of C in tyrosine was observed in solid state ¹³C NMR spectra, so that it further proved the cross-linking PGDE with tyrosine residue. It is supposed that an intermolecular network structure can be formed by the cross-linking between PGDE and tyrosine, histidine and lysine residue of silk fibroin, which make CFG homogeneous and with better transparence and flexibility.

Key words: Silk fibroin, Gel, Chemical cross-linking, Epoxide