Generalized direct fabrication of embedded-magnet microrobots with enhanced material compatibility

Magnetically actuated microrobots offer transformative potential for biomedical applications such as targeted drug delivery and minimally invasive diagnostics. However, existing fabrication methods are constrained by challenges in magnetic material integration, structural robustness, and reproducibility. In this work, we present an improved direct-printing strategy that integrates permanent micro-magnets into microrobots during the two-photon polymerization (TPP) process, thereby eliminating the need for post-assembly alignment or insertion. To enhance magnetic-material compatibility and interfacial reliability, a sputtering-based surface modification technique is introduced, enabling robust integration of both pre-coated and surface-treated magnets. Using this approach, four functional microrobotic platforms are demonstrated: (1) a helical microswimmer for efficient propulsion, (2) a micro-scale tumbling microrobot for terrain locomotion, (3) a compliant micro-gripper for precise grasping and manipulation, and (4) a mini-MicroTumbler (MMT) incorporating a sputter-modified magnet for stable microscale actuation. Performance characterization was conducted under varying actuation frequencies and environments. The microswimmer exhibited frequency-dependent propulsion consistent with magnetic step-out behavior, the MicroTumbler achieved stable locomotion across inclined surfaces, the micro-gripper demonstrated controllable deformation and object manipulation, and the MMT showed reliable frequency-dependent motion. This study establishes a scalable, material-flexible, and high-fidelity fabrication method for embedded-magnet microrobots, broadening the design space and enabling the next generation of multifunctional, magnetically actuated microsystems.