In‐Process Magnetization for 3D Printing of Magnetorheological Elastomer with Heterogeneous Magnetic Profile for Anisotropic Actuation

Soft magnetic actuators have gained significant interest for applications in minimally invasive medical robots, artificial muscles, soft robotic manipulators, and wearable bioelectronic interfaces, yet their functionality remains fundamentally limited by current magnetization strategies. To this end, a novel in‐process printing and magnetization strategy with spatial and dynamic control of an external magnetic field during printing is developed to fabricate magnetorheological elastomers with fully customizable three‐dimensional (3D) magnetization profiles. This method allows localized magnetic domain alignment in arbitrarily programmed orientations within a solid, enabling anisotropic actuation at micron to millimeter scales. The proposed method is highly sensitive to curing kinetics, material viscosity, and magnet positioning, which are characterized theoretically, experimentally, and in simulation. Structures magnetized in this way offer robust strain‐sensing, information‐encoding, and bio‐inspired heterogeneous actuation capabilities. Demonstrations highlight this versatility, including a dragonfly with oppositely magnetized wings for tunable resonant actuation, an octopus‐inspired swimmer whose magnetized legs reproduce aquatic locomotion, and a serpentine catheter with high degrees of freedom across 6 magnetic nodes. Together, these advances establish a versatile platform for designing magnetically responsive systems that couple programmable anisotropic actuation with biological complexity.