Curving-Stretching\nInduced Alignment in Hydrogel Actuators\nfor Enhanced Grip Strength and Rapid Response

Natural tissues, like ligaments and tendons, display\nnot just robust\nmechanical performance but also complex anisotropic structures extending\nbeyond one-directional arrangements. However, fabricating hydrogel\nactuators with biomimetic three-dimensional anisotropy remains challenging.\nHerein, a simple strategy involving curving-stretching induced alignment\nis proposed to prepare anisotropic Fe<sup>3+</sup>-cross-linked poly(acrylic\nacid)-poly(acrylamide) hydrogel actuators. These hydrogels exhibit\nexceptional mechanical properties, boasting a fracture stress of 7.1\nMPa and a superior modulus of 33.2 MPa when prestretched to 200% strain,\nwhich are 2.3 times and 4.9 times higher than their unstretched counterparts.\nThe stretched anisotropic hydrogel gripper, stronger than its unstretched\ncounterpart, can lift heavy objects while also achieving rapid responsiveness\nto stimuli. This work introduces a novel and effective method for\nfabricating anisotropic hydrogels, highlighting their broad applicability\nin fields such as soft robotics, biomedical devices, and beyond.