A novel soybean protein/polyacrylamide (SPI/PAAm) composite hydrogel was synthesized, in which soybean protein (SPI) and acrylamide (AAm) were used as raw materials, ammonium persulfate (APS) was used as the initiator, N, N'-methylenebisacrylamide (MBAA) was used as the covalent crosslinker, CaCl2 was used as the ionic crosslinker and N, N, N', N'-tetramethylethylenediamine (TEMED) was used as the accelerator. The structure and mechanical properties of the obtained hydrogels were analyzed, and the mechanical mechanism was then investigated. The results suggest that the obtained hydrogel had a double-network structure, including ionically-crosslinked soybean protein network and covalently-crosslinked polyacrylamide network. For the double-network hydrogel, the ionically-crosslinked network dispersed the applied stress and dissipated the energy, and the covalently-crosslinked network contributed to the shape retention. The synergistic effect resulting fromdouble networks endowed the hydrogel with high elasticity, high compressibility and fatigue resistance.The morphology analysis revealed that the obtained hydrogel showed a uniform cell structure, and the soybean protein was uniformly distributed within the hydrogel. The mechanical analysis indicated that the obtained hydrogel exhibited high compression-resilience property and elasticity, which could rapidly recover to its original shape upon 80% compressive strain without structural collapse or damage during 10 successive uniaxial compression cycles. More encouragingly, the obtained hydrogel possessed outstanding toughness and fatigue resistance, which could remain shape intact after undergoing 100 compression cycles at 20%, 50% and 80% strain, respectively.After 100 compression cycles at 20%, 50% and 80% strain, the corresponding stress remaining rates were 90%, 95% and 104%, the corresponding plastic deformation rates were 3.1%, 5.9%and 8.4%, and all the energy loss coefficients were below 0.3.
