A seed-inspired 3D electroionic flier with obliquely embossed ionic polymer actuators for tunable autorotation and lift

Abstract

In nature, many plants disperse their seeds with simple wing structures that ride the wind, slow descent, and carry propagules farther. These natural flight morphologies offer blueprints for low-mass, passively stable autorotation and lift generation. Despite extensive seed-mimicking efforts based on this inspiration, most research using stimuli-responsive actuators has focused on reproducing simple bending-dominated shapes rather than on the kinematic flight control of seeds, resulting in only a limited mimicry of the aerodynamic flight of seeds. Here we demonstrate a geometry-programmed ionic polymer actuator approach that enables controllable autorotation in three-dimensional electroionic fliers. Embossed Nafion membranes are patterned so that the pitch sets the magnitude of bending bias and the oblique orientation induces twist, resulting in coupled bending-twisting motion. Asymmetry varies non-monotonically with pitch, reaching at maximum at 1.6 mm, arising from the interplay between reduced ion-ion repulsion at the patterned surface and mechanical stiffening from rib-like surface relief. At 1.5 V and 0.1 Hz sinusoidal input, peak displacements reach -2.76/2.04 mm (embossed/smooth), whereas square-wave input increases displacement to -3.71/2.66 mm and raises asymmetry from 0.72 to 1.05 mm. Assembled from these actuators, a 3D electroionic flier emulating the aerodynamic mechanisms of two different wind-dispersed seeds exhibits a descent speed of 2.980 m s⁻¹ in a drop test, the lowest among the tested fliers. These results position geometry-programmable ionic polymer actuation as a scalable pathway to autorotation and lift tuning, which should allow the realization of advanced seed-mimetic deployment systems and soft aerial microrobots.