Collective and Rapid High Amplitude Magnetic Oscillation of Anisotropic Micropillar Arrays.

Magnetic soft actuators allow high-frequency shape reconfiguration of the micropillar array by rapid rotation of an external magnetic field; however, viscoelastic soft actuators cannot instantaneously reach an equilibrium deformation state to minimize the magnetic moment at a given short time scale, resulting in a significant reduction of the strain amplitude. Herein, we report high-frequency magnetic oscillation of a micropillar array without significant reduction in frequency or strain amplitude by programming the magnetization direction of hard magnetic microparticles embedded in a soft elastomer. Various oscillatory motions, including bending, twisting, and torsion under time-varying external magnetic fields, are demonstrated via programming the magnetization of anisotropic micropillars. Hybridization of microparticles and nanorods in magnetic composites improves the magnetic amplitude of micropillars through a synergistic effect. The translation of microscopic oscillatory motion into a macroscopic function is achieved by the rapid and large-amplitude magnetically programmable collective deformation of the micropillar array. Collective oscillatory torsion of the micropillar array functions as the legs in a walking robot as well as micropaddles that can program the chirality of the liquid flow. Point- or line-symmetric torsion enables the flow direction (counterclockwise or clockwise) to be programmed according to the direction of applied magnetic field to the micropillar array.