UV Light‐Mediated Hydrolytic Reaction to Develop Magnetic Hydrogel Actuators with Spatially Distributed Ferriferous Oxide Microparticles

Magnetic hydrogel actuators are developed by incorporating magnetic fillers into the hydrogel matrix. Regulating the distribution of these fillers is key to the exhibited functionalities but is still challenging. Here a facile way to spatially synthesize ferrosoferric oxide (Fe 3 O 4 ) microparticles in situ in a thermal‐responsive hydrogel is reported. This method involves the photo‐reduction of Fe 3+ ions coordinated with carboxylate groups in polymer chains, and the hydrolytic reaction of the reduced Fe 2+ ions with residual Fe 3+ ions. By controlling the irradiation time and position, the concentration of Fe 3 O 4 microparticles can be spatially controlled, and the resulting Fe 3 O 4 pattern enables the hydrogel to exhibit complex locomotion driven by magnet, temperature, and NIR light. This method is convenient and extendable to other hydrogel systems to realize more complicated magneto‐responsive functionalities.