Bioinspired 2D Isotropically Fatigue-Resistant Hydrogels.

Engineering conventional hydrogels with muscle-like anisotropic structures could efficiently increase the fatigue threshold over 1,000 J m-2 along the alignment direction. However, fatigue threshold in perpendicular to the alignment was still as low as 100∼300 J m-2 , making them non-suitable for those scenarios where isotropic properties are desired. Here, inspired by the distinct structure-properties relationship of heart valves, we report a simple yet general strategy to engineer conventional hydrogels with unprecedented yet isotropic fatigue resistance, with a record-high fatigue threshold over 1,500 J m-2 along two arbitrary in-plane directions. Our two-step process involves the formation of preferentially-aligned lamellar micro/nanostructures through a bidirectional freeze-casting process, followed by compression annealing, synergistically contributing to extraordinary resistance to fatigue crack propagation. Our study provides a viable means of fabricating soft materials with isotropically extreme properties, thereby unlocking paths to apply these advanced soft materials toward applications including soft robotics, flexible electronics, e-skins and tissue patches. This article is protected by copyright. All rights reserved.