Micropores can enhance the intrinsic fracture energy of hydrogels

Hydrogels, a class of soft materials composed of a polymer chain network, are widely known to be prone to fatigue failure. To understand the underlying mechanisms, we simulate polymer scission and fatigue initiation in the vicinity of a crack tip within a two-dimensional polymer network. For a network without pores, our findings reveal that polymer scission can occur across multiple layers of chains, rather than just a single layer as assumed in the classical Lake-Thomas theory, consistent with previous studies. In contrast, for a network with a high density of micropores, our results demonstrate that the pores can substantially enhance the intrinsic fracture energy of the network in direct proportion to the pore size. This enhancement is attributed to pore-pore interactions, which lead to a relatively uniform distribution of cohesive energy ahead of the crack tip. Our model suggests that incorporating micropores could be a promising strategy for improving the intrinsic fracture energy of hydrogels and that natural porous tissues may have evolved to achieve enhanced fatigue resistance.