Self-Oscillating Helix Showing Amplified Winding and Unwinding Motions.

Abstract

Helical architectures in nature amplify motion via winding-unwinding. We report a simple, universal photopolymerization strategy to fabricate hydrogel helices with precisely controlled radial polymer gradients inside glass capillaries. A helically wrapped photomask and a chemical UV absorber (Ru(bpy)₃) jointly encode longitudinal and radial asymmetry. Their geometry is readily programmed by adjusting the photomask width and spacing, and our approach is polymer-general, including thermoresponsive gels and organogels. As a representative example, lower critical solution temperature (LCST)-type poly(NIPAAm) helices convert small, isotropic volume change into amplified uniaxial deformation, showing 1.6-fold larger axial shrinkage than their total length shrinkage under heating. They respond to various stimuli, including temperature, acid, and near-infrared (NIR) light. As a proof-of-concept soft robotic actuator, we fabricated a helix with a gradual axial variation in diameter and demonstrated stepwise, unidirectional locomotion along a string under cyclic heating and cooling. Integrating vinyl‑functionalized Ru(bpy)₃ as a covalent catalyst yields self‑oscillating helices driven by the Belousov-Zhabotinsky reaction, which autonomously repeat winding-unwinding accompanied by peristaltic waves. Compared with conventional rods, helices exhibit four-fold larger amplitude and 3.4-times faster deswelling kinetics. Our platform establishes a geometry‑driven design rule that harnesses helical coupling to amplify displacement in programmable and autonomous soft actuators.