Stimuli-responsive hydrogels with self-strengthening properties are promising for the use of autonomous growth and adaptation systems to the surrounding environments by mimicking biological materials. However, conventional stimuli-responsive hydrogels require structural destruction to initiate mechanochemical reactions to grow new polymeric networks and strengthen themselves. Here we report continuous self-strengthening of a nanocomposite hydrogel composed of poly(N-isopropylacrylamide) (PNIPAM) and nanoclay (NC) by using external stimuli such as heat and ionic strength. The internal structures of the NC-PNIPAM hydrogel are rearranged through the swelling–deswelling cycles or immersing in a salt solution, thus its mechanical properties are significantly improved. The effects of concentration of NC in hydrogels, number of swelling–deswelling cycles, and presence of salt in the surrounding environment on the mechanical properties of hydrogels are characterized by nanoindentation and tensile tests. The self-strengthening mechanical performance of the hydrogels is demonstrated by the loading ability. This work may offer promise for applications such as artificial muscles and soft robotics.

中文翻译：

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自强化刺激响应纳米复合水凝胶

具有自强化特性的刺激响应水凝胶有望通过模仿生物材料来使用自主生长和适应周围环境的系统。然而，传统的刺激响应水凝胶需要结构破坏才能引发机械化学反应，从而生长出新的聚合物网络并增强自身。在这里，我们报告了由聚（N-异丙基丙烯酰胺）（PNIPAM）和纳米粘土（NC）通过使用外部刺激如热和离子强度。NC-PNIPAM水凝胶的内部结构通过溶胀-消溶胀循环或浸泡在盐溶液中进行重新排列，从而显着提高其机械性能。水凝胶中 NC 的浓度、溶胀-消溶胀循环的次数以及周围环境中盐的存在对水凝胶机械性能的影响通过纳米压痕和拉伸试验进行了表征。负载能力证明了水凝胶的自强化机械性能。这项工作可能为人造肌肉和软机器人等应用提供希望。