Orientational Co Nanorod-Enabled Ferromagnetic Hydrogel Actuators with Diverse Hosts

Magnetic hydrogel actuators have promising applications in soft robots, wastewater treatment, and underwater detection due to the advantages of their remote control and high magnetic penetration. However, their controllability is limited by the general fabrication methods of doping paramagnetic nanoparticles and nonuniform ferromagnetic nanoparticles with a weak or nonconfigurable magnetic distribution. Herein, we report a kind of ferromagnetic hydrogel actuator comprising oriented ferromagnetic Co nanorods with high magnetic anisotropy, and the magnetic domains can be flexibly programmed by external fields. To demonstrate the generality of the approach and to research how the flexibility of the hydrogel hosts influences the behavior of the actuators, three kinds of hydrogel hosts have been used, including silica hydrogel, cellulose hydrogel, and clay hydrogel. The silica hydrogel actuators provide a holistic response. The cellulose hydrogel actuator can achieve a certain degree of deformation. The clay hydrogel actuators are capable of achieving large deformations such as the knot and the bow-knot. Furthermore, biomimetic actuators with the capacities for wriggling, paddling, and climbing simple obstacles are designed by utilizing the bending deformations of the clay hydrogel. In conclusion, this work provides an alternative strategy for designing and fabricating magnetically actuated hydrogel actuators for imitating biological units or constructing soft robots by regulating the orientation and distribution of ferromagnetic nanoparticles.