Starfish‐Inspired Cut‐Resistant Hydrogel with Self‐Growing Armor: Where Softness Meets Toughness

Abstract Many soft animals like starfish have developed armors to protect their soft bodies in order to survive in harsh environment. Inspired by this fact, special hydrogels with self‐growing protective armors are developed by allowing sodium acetate to crystallize on hydrogel surface. Poly(acrylic acid) chains limit the crystalline region to the surface of the hydrogel by decreasing the pH value and limiting the movement of ions, and then creating a set of tough armor. This armor‐protected hydrogel is able to withstand a high pressure (> 78 MPa) under cutting and prevent the penetration of sharp objects. Interestingly, the unique stimulated‐precipitation mechanism allows the armor to repair itself after damage. Besides, the surface of hydrogel changes from “sticky” to “slippery”, which also helps to improve its protective ability. Moreover, the armor helps to retrain water in hydrogel network, and significantly improve the mechanical properties of hydrogels (maximum compressive stress >18 MPa, compressive strain > 90%). In addition, the hydrogel can keep soft and work durably at extreme temperatures (−50 °C and 80 °C) due to the high salt concentration. This study provides an innovative approach for designing armor‐protected hydrogels with great potential in engineering applications such as actuators and sensors for harsh environments.