Silk fibroin (SF) hydrogels were obtained from both domestic (Bombyx mori) and wild (Antheraea pernyi) silkworms from aqueous silk fibroin solutions at room temperature. The gelation time of the Antheraea pernyi (A. pernyi) SF solution was significantly shorter than that of the Bombyx mori (B. mori) SF solution. The secondary structures of the two kinds of hydrogels were also compared. In order to further reduce the gelation time, various amounts of polyethylene glycol (PEG) were blended with the silk fibroins of A. pernyi and B. mori. The gelation time of both A. pernyi SF and B. mori SF decreased with the increased amount of PEG. After freeze-drying, the hydrogels were characterized through X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and Raman spectroscopy. Results showed that the addition of polyalcohol did not change the main secondary structure of the hydrogels. However, the addition of polyalcohol did reduce the gelation time and triggered additional formation of β-sheets.

The rapid manufacture of silk fibroin gels in mild conditions is an important subject in the field of silk-based biomaterials. In this study, the gelation of Antheraea pernyi silk fibroin (ASF) aqueous solution was induced by shearing, without chemical cross-linking agents. Simple shearing controlled and accomplished the steady and rapid conformational transition to β-sheets with ease. The conformational transformation and rapid gelation mechanisms of ASF induced by shearing were tracked and analyzed by circular dichroism spectrometry, Fourier transform infrared spectroscopy and X-ray diffractometry, then compared with Bombyx mori silk fibroin (BSF). ASF quickly formed hydrogels within 24-48 h after shearing under different shearing rates for 30-90 min, resulting in sol-gel transformation when the β-sheet content reached nearly 50%, which is the minimum content needed to maintain a stable hydrogel system in ASF. The gel structures remained stable once formed. The rapid gelation of ASF through shearing compared with BSF was achieved because of ASF's alternating polyalanine-containing units, which tend to form α-helix structures spontaneously. Further, the entropic cost during the conformational transition from the α-helix to the β-sheet structure is less than the cost of the transition from the random coil structure. This method is a simple, non-chemical cross-linking approach for the promotion of rapid gelation and the protection of the biological properties of ASF, and it may prove useful for application in the field of biomedical materials.

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