The relationship between strength and elasticity in silk hydrogels by inter-vs. intramolecular β-sheet formation

Silk fibroin (SF) is most commonly used in tissue engineering and regenerative medicine due to its excellent biocompatibility and mechanical strength. In particular, SF hydrogels can mimic the three-dimensional extracellular matrix (ECM), offering a supportive environment for cellular activities. However, their mechanical properties are difficult to precisely control, which limits their application in load-bearing or function-specific tissue scaffolds. Mechanical performance in SF hydrogels is primarily governed by changes in secondary structure, especially β-sheet formation, which correlates with crystallinity and physical crosslinking. Most prior studies have focused on the total amount of β-sheet content, overlooking how its arrangement—intermolecular versus intramolecular—within the three-dimensional hydrogel network influences functional behavior. In this study, we systematically analyzed the relationship between β-sheet structural arrangement and physical properties by applying post-treatment with three different solvents—PBS buffer, methanol (MeOH), and dimethylformamide (DMF)—following UV-induced crosslinking of methacrylated SF (Sil-MA) hydrogels. PBS was used as a control mimicking physiological conditions, while MeOH and DMF were selected for their distinct β-sheet induction mechanisms. The results demonstrated that MeOH rapidly induces intermolecular β-sheet stacking and lamellar structure, enhancing stiffness, while DMF promotes intramolecular folding and β-turns, increasing elasticity. These molecular-level structural differences were directly linked to variations in swelling, degradation rate, and mechanical responses. Overall, the findings provide a scientific basis for controlling the functional performance of silk hydrogels by modulating post-treatment conditions, which will enable the precise design of custom bioscaffolds for regenerative applications requiring specific combinations of elasticity and strength.