H₂O₂-Assisted Fabrication of Stiff and Tough Hydrogel Using Natural Cysteine-Rich Protein

Protein-based hydrogels have emerged as an important class of materials for biomedical applications. However, these hydrogels often exhibit inferior mechanical properties, significantly limiting their potential applicability. Herein, a simplified yet efficient soaking method is developed to broaden the scope of constructing stiff and tough pure protein hydrogels, using natural cysteine-rich proteins, such as lactoferrin (LF). The preformed, soft and brittle, unfolded protein hydrogels transformed into highly stretchable and compressible elastomers after soaking in H₂O₂ due to chain entanglement and self-crosslinking via interchain disulfide bonds. As a result, the H₂O₂-treated LF hydrogels exhibited an extraordinary ultimate strength (compressive and tensile strains of over 90% and 400%, respectively, and stresses of 20 and 1.5 MPa). In addition, these rubber-like hydrogels exhibited exceptional self-recovery and fatigue resistance capabilities. Furthermore, the relationship between protein structure and the mechanical properties of the hydrogel was investigated. Together, these revelations could serve as a guiding principle for advancing the design of biocompatible, tough protein hydrogels without chemical modification or mechanical reinforcing fillers.