Programming of Complex Magnetic Profiles Enforced by 4D Printed Magnetic LCE Actuators.

Magnetic soft actuators enable untethered, contact-free actuation yet they are fundamentally limited by the difficulty of programming complex, three-dimensional (3D), spatially non-uniform magnetic profiles. Here, we introduce a four-dimensional (4D) printing-enabled magnetic programming strategy that overcomes this challenge by magnetizing magnetically active liquid crystal elastomers (MLCEs) in thermally actuated target states. Digitally prescribed director architectures define deterministic 3D deformations at elevated temperature, which serve as intrinsic programming templates during magnetization under a spatially uniform magnetic field. Upon cooling, relaxation of the thermomechanical deformation transforms the initially uniform magnetization into a complex, spatially varying magnetic profile that encodes the target shape as a magnetically favoured configuration. This approach enables the recovery of thermally defined shapes at room temperature under low magnetic fields and allows bidirectional and multistate actuation via simple reversal of field direction. By integrating spatial magnetic programming with controlled geometric asymmetry, we demonstrate frequency-tunable linear locomotion and chirality-encoded clockwise or anticlockwise rotational motion in multimaterial soft robotic architectures. This strategy decouples magnetic profile complexity from magnetization hardware, providing a scalable, template-free route to fully 3D magnetic programming for soft robotics and untethered actuators operating under low-field conditions.