A comparative study of the mechanical properties of hybrid double-network hydrogels in swollen and as-prepared states

in the swollen state. The agar/PAM DN gels can readily achieve swelling ratios in the range of ∼1.3-3.6 by adjusting the concentrations of the first network, the second network, and the crosslinker. The swelling capacity of the agar/PAM DN gels was balanced by the competition between the "non-swellable" agar network and the "highly swellable" PAM network, indicating that the first and second networks play different roles in the swelling-induced mechanical properties of the agar/PAM gels. Based on a comparison of the tearing and tensile behaviors of the hybrid DN gels between both as-prepared and swollen gels, we proposed a swelling-induced fracture mechanism that is different from those of SN and chemically-linked DN hydrogels. This work not only demonstrates a very tough swollen DN gel with a hybrid network, but also provides a better understanding of the swelling characteristics of hybrid DN gels, which hopefully helps to offer some valuable insights into the development of next-generation tough hydrogel materials in both as-prepared and swollen states.