Gravity-resisting directional climbing of magnetic-assembled microwheels on the vertical wall

Microscale wall-climbing robots hold transformative potential for biomedical applications, however, their further miniaturization is hampered by the inability to achieve efficient surface adhesion at the microscale. Here, we present a rotating magnetic field-driven strategy for a magnetic microwheel to achieve gravity-resisting directional climbing on vertical walls, including biological tissue surfaces. By modulating the rotating magnetic field strength, orientation, wedge angle between the microwheel and the vertical wall, stable hydrodynamic interactions are induced, generating controllable wet friction force to counteract gravity. Experiments demonstrate that the climbing direction of microwheels can be dynamically adjusted on demand by regulating the magnetic field strength, wedge angle, and the angle between the magnetic field plane and the z-axis, enabling precise locomotion on vertical, overhanging, and biological tissue surfaces. Reversing the magnetic field and symmetrically adjusting the wedge angle along the z-axis further allows programmable directional switching. This approach circumvents the limitations of traditional negative-pressure adhesion mechanisms at microscales, offering a novel paradigm for integrating actuation and motion control in miniature wall-climbing robots. The strategy significantly expands the application scope of wall-climbing robots in biomedical scenarios, such as targeted drug delivery and minimally invasive surgery, while providing insights for designing multifunctional microrobots with adaptive locomotion capabilities.