Bioinspired spatiotemporal control of microhelix formation and actuation.

Helical structures provide critical functions in structural stability, locomotion, and mechanical flexibility. Among the helical structures, the dynamic coiled tendril formation in climbing plants upon contact with support structures inspires the development of numerous helix-based actuators and soft robotics. However, achieving precise spatiotemporal control over helix formation and actuation at the microscale remains a challenge. We introduce a materials system in which the spatial location and dynamics of helix formation are governed by the intrinsic bending resulting from the differential swelling of polyacrylic acid copolymer hydrogels, with electric fields serving as the primary control for electroosmotic flow-induced swelling/deswelling phase transitions. By manipulating electric field polarity and using patterned substrates, we achieve reversible spatiotemporal control over helix formation and actuation. The swelling/deswelling mechanism enables the applications of rotary actuation and controlled microsphere capture-release. Our approach represents a notable advancement in the precise dynamical control of helix formation, opening avenues for the development of sophisticated microactuators and artificial muscle systems.