Shape-morphing active particles with invertible effective polarizability for configurable locomotion and steering

Active particles are analogs of microorganisms in that they locally dissipate energy to propel in low Reynolds number fluids. However, most active particles lack the ability to undergo controlled shape transformations that change how they move in response to environmental cues. Here, we present a class of stimuli-responsive active particles that exhibit fully reversible, shape-dependent propulsion. The particles consist of a bilayer of a thermoresponsive hydrogel and a non-swelling glassy polymer, patterned into rectangular microscale prisms. Temperature changes near the phase transition of hydrogel cause large curvature shifts, from flat plates at 35 °C to crescent shapes at 20 °C, accompanied by changes in effective polarizability. When powered by AC electric fields, this coupling between geometry and polarizability enables programmable propulsion modes including linear and helical motions. Sequential temperature changes allow encoded in situ steering, establishing a design principle for microscale active systems capable of adaptive propulsion and reconfiguration. Most active particles studied to date lack the ability to undergo controlled shape transformations and control over their propulsion in response to environmental stimuli. Here, the authors present a class of active particles made from stimuli-responsive materials that exhibit fully reversible shape-dependent propulsion.