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 )^−0.58 at 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.

中文翻译：

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琼脂基杂化双网络水凝胶的速率依赖性断裂行为

具有高抗裂性的柔软而坚韧的水凝胶的先进开发显着扩展了其应用范围，从组织工程的生物医学应用到软柔性设备的新兴电子应用。我们研究了琼脂/PAAm 混合双网络 (DN) 水凝胶在不同应变率下的断裂韧性。在没有预切割的大变形中，琼脂/PAAm杂化DN水凝胶的加载-卸载曲线表现出与速率无关的滞后。然而，预切琼脂/PAAm杂化DN水凝胶的断裂韧性在应变率（ε̇）0.12 s ^{–1附近表现出一个过渡区域，并且在ε̇ < 0.12 s –1}处观察到与速率无关的韧性，而断裂韧性下降如果 ε̇ > 0.12 s ^–1则显着。我们还发现，在高应变率下，断裂韧性随应变率变化为 Γ ∼ (dλ/d t ) ^-0.58 。提出了一种可能的机制来解释这种现象。人们相信这项工作为混合 DN 凝胶的断裂行为提供了新的见解。