Three-dimensional reconfigurable magnetic microswarms with boundary-transcending capabilities.

Swarm behaviors are prevalent in nature and have inspired many engineering designs. However, achieving artificial swarms capable of reversibly migrating through fluids against gravity and transcending physical boundaries, such as solid-liquid and liquid-air interfaces, remains challenging. Here, we propose a strategy for generating enhanced rotating magnetic fields by synchronizing a global rotating field with a co-rotating local gradient. This enables three-dimensional (3D) movement of magnetic microparticles independent of physical boundaries and leads to reconfigurable collective behaviors, including reversible transitions between 2D and 3D tornado-like patterns, as well as between single and dual microswarms collectives. The generated tornado-like microswarm induces convection flows that enable entrapment and transport of substances within a confined spatial domain. This capability was used to promote chemical reaction within a confined region. As a further demonstration, the cardiotoxic compound-levamisole was vertically transported across intermediate barriers to induce localized arrhythmic beating of cardiomyocytes. These multifunctional magnetic microswarms hold promise for biological mechanism discovery and drug screening.