Rate-Dependent Fracture Behaviors of Agar-Based Hybrid Double-Network Hydrogels

The advanced development of soft yet tough hydrogels with high crack resistance significantly extends their application scope from biomedical applications for tissue engineering to emerging electronics applications for soft flexible devices. We investigated the fracture toughness of agar/PAAm hybrid double-network (DN) hydrogels at various strain rates. In large deformations without precut, the loading–unloading curves of agar/PAAm hybrid DN hydrogels exhibit rate-independent hysteresis. However, the fracture toughness of the precut agar/PAAm hybrid DN hydrogel exhibits a transition region around strain rate (ε̇) as 0.12 s–1, and rate-independent toughness is observed at ε̇ < 0.12 s–1, while the fracture toughness decreases significantly if ε̇ > 0.12 s–1. We also discover that the fracture toughness scales with strain rate as Γ ∼ (dλ/dt)−0.58at a high strain rate. A possible mechanism is proposed to interpret this phenomenon. It is believed this work provides new insight into the fracture behavior of hybrid DN gels.