Supramolecular hydrogel actuators with reprogrammable magnetic orientation by locally mediated viscoelasticity and pinning force.

Magnetic soft actuators with reprogrammable deformations have gained substantial attention due to their adaptability for various applications. However, achieving precise and local reorientation of magnetic particles remains challenging. Here, we present a strategy to locally tailor the viscoelasticity of magnetic supramolecular hydrogels, facilitate reorientation of the embedded magnetic particles, and enable reprogrammable magnetoactuated deformation and locomotion of the composite gels. The magnetic hydrogels are facilely prepared by mixing neodymium-iron-boron particles with an aqueous poly(acrylic acid--acrylamide) solution, which spontaneously forms supramolecular network with carboxylic-ferric ion coordinates as physical cross-links. This network enables dynamic control of viscoelasticity by localized laser heating, which reduces the pinning force of gel matrix and allows for reorientation of magnetic particles under a modest magnetic field. We demonstrate that the same hydrogel sheet can be reprogrammed to exhibit various complex deformations and locomotion. This versatile approach to developing magnetic hydrogels with adaptive responses offers exciting potential for soft robotics and biomedical devices.