Silk fibroin (SF) is a natural polymer with low immunogenicity and good biocompatibility. However, most silk-based hydrogels formed through chemical or physical cross-linking are brittle, the preparation of which also inevitably introduces cytotoxic cross-linking agents. Herein, a simple strategy is presented for synthesizing SF hydrogels with tunable mechanical properties by combining γ-ray radiation with ethanol treatment. Neither toxic initiators nor chemical agents are utilized during the whole preparation procedure. For “soft” hydrogels, the compressive moduli are less than 29 kPa (SF-S hydrogels), while for “tough” hydrogels, the compressive moduli are between 1.21 and 2.41 MPa (SF-D hydrogels). Specifically, γ-ray radiation makes SF form uniform and stable chemical cross-linking sites within and between molecular chains, resulting in “soft” and highly elastic SF hydrogels. The physical cross-linking via ethanol treatment leads to the self-assembly of fibroin chains, transforming those soft hydrogels to tough hydrogels. These double cross-linked SF hydrogels (SF-D hydrogels) exhibit excellent mechanical strength. Effects of various cross-linking conditions on the secondary structure, pore structure, mechanical properties, gelation degree, swelling, and in vitro degradation properties are explored. A series of cell experiments demonstrate that the SF hydrogels with different mechanical strength can stimulate the expression of specific genes of rat bone marrow mesenchymal stem cells (BMSCs) in various differentiation directions. These results also show the application prospects in tissue engineering by customizing hydrogels for the mechanical strength of different tissues.

中文翻译：

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γ射线交联高可调弹性丝素蛋白水凝胶的结构和力学性能研究

产生“柔软”和高弹性的SF水凝胶。通过乙醇处理的物理交联导致丝心蛋白链的自组装，将这些软水凝胶转化为坚韧的水凝胶。这些双交联SF水凝胶（SF-D水凝胶）表现出优异的机械强度。不同交联条件对二级结构、孔结构、力学性能、胶凝度、溶胀度和溶胀度的影响探索了体外降解特性。一系列细胞实验表明，不同机械强度的SF水凝胶可以刺激大鼠骨髓间充质干细胞（BMSCs）特定基因在不同分化方向的表达。这些结果还显示了通过针对不同组织的机械强度定制水凝胶在组织工程中的应用前景。