Light and Magnetic Control of Hydrogel Robots

Engineering responses of soft materials at hierarchical time and length scales is of great interests to both scientific and engineering communities. By hybridizing soft materials with various functional nanocomponents, the responses of composites can be manipulated via external stimuli such as heat, light, and magnetic/electric fields, etc. We report here on the design of hydrogels containing aligned ferromagnetic nanowires dispersed in a polymer network that change shape in response to light and experience torques in rotating magnetic fields. Such dual responsiveness enables the control of the hydrogel morphologies and its robotic behaviors include walking, steering, climbing, rolling and delivery of cargo. The theoretical description of both light and magnetic response allowed us to program specific trajectories of hydrogel objects that were verified experimentally.