Hybrid magnetic-electric actuation for enhanced motion control and multi-surface operation of Janus microrobots.

This study presents a hybrid actuation framework for enhanced and automated control of Janus particle microrobots across multiple surfaces. Under various magnetic and electric field combinations, Janus particles act as active microscale agents with diverse propulsion and navigation modes on a single surface, while their electric response additionally provides frequency-modulated functionalities such as reversible cargo loading. Here, we show that by further leveraging magnetic levitation and electrostatic trapping at a microchamber ceiling against gravity, these particles can transition between surfaces on demand, extending their mobility beyond the limitations of many traditional microrobots which are surface-bound. This approach grants access to three-dimensional workspaces without continuous surface contact, enabling capabilities such as vertical obstacle crossing, navigation of elevated surfaces, discrete surface patterning, and cargo transport between surfaces. Together, these developments establish a versatile micro-robotic platform applicable in microfluidic and lab-on-a-chip systems, and may further inspire microrobot designs utilizing controlled inter-surface transitions.