Stable magnetic soft structures.

Magnetic soft structures are highly versatile in unstructured environments, making them attractive for minimally invasive medical devices. However, this versatility also renders them susceptible to unintended deformations under fluctuating magnetic fields. The challenge is further compounded by medical imaging limitations that hinder accurate estimation of device pose and shape and by anatomical boundaries that enforce misalignment with the field. Collectively, these factors can cause uncontrolled shape change and functional failure. Here, we focus on slender magnetic soft structures to investigate their stability under misaligned fields. Our anisotropic design, achieved through flexural joints, yields ~52-fold higher bending stiffness in the preferred direction and ~18-fold higher torsional stiffness than isotropic beams. This structure serves as a building block for stable spiral tentacles, helices, planar sheets, expandable devices, cubes, and three-dimensional tessellation. We validate robustness through wormlike self-propulsion, guidewire navigation with 30-fold lower insertion force, and capsule peristaltic locomotion, advancing safer, more controllable devices.