Coupling Magnetic Torque and Force for Colloidal Microbot Assembly and Manipulation

For targeted transport in the body, biomedical microbots (mu bots) must move effectively in three-dimensional (3D) microenvironments. Swimming mu bots translate via asymmetric or screw-like motions while rolling ones use friction with available surfaces to generate propulsive forces. Previously the authors have shown that planar rotating magnetic fields assemble mu m-scale superparamagnetic beads into circular mu bots that roll along surfaces. In this, gravity is required to pull mu bots near the surface; however, this is not necessarily practical in complex geometries. Here, the authors show that rotating magnetic fields, in tandem with directional magnetic gradient forces, can be used to roll mu bots on surfaces regardless of orientation. Simplifying implementation, a spinning permanent magnet is used to generate differing ratios of rotating and gradient fields, optimizing control for different environments. This use of a single magnetic actuator sidesteps the need for complex electromagnet or tandem field setups, removes requisite gravitational load forces, and enables mu bot targeting in complex 3D biomimetic microenvironments. A spinning permanent magnet can be used to generate differing ratios of rotating and gradient fields to assemble, spin, and pull microbots toward a surface. This use of a single magnetic actuator sidesteps the need for complex electromagnet setups, removes requisite gravitational load forces, and enables microbot targeting in complex 3D biomimetic microenvironments.image (c) 2023 WILEY-VCH GmbH