Single-parameter programmed thermomechanical actuation via 3D-printed helical director fields in liquid crystal elastomers

Abstract

Abstract Stimuli-responsive material like liquid crystal elastomers (LCEs) hold great promise for untethered soft machines, yet conventional extrusion-based 3D printing restricts their molecular alignment strictly to the uniaxial deposition path. This inherent constraint strongly couples the actuation mode to the printed geometry, typically requiring complex multi-material architectures or spatially structured stimuli to achieve multimodal behaviors. Here we introduce a rotational 3D printing approach that embeds a helical director field within LCE filaments, enabling multimodal actuation controlled by a single fabrication parameter: the helix angle ( θ ). Tuning θ programs each filament to contract, elongate, twist or remain macroscopically invariant when heated, decoupling actuation from device geometry. Spatial gradients in θ create a hierarchy of activation temperatures, yielding sequential shape changes under uniform heating. Localized heating of the magnetic-LCE composite segments allows their magnetic domains to be reoriented, making the shape programs rewritable and enabling switchable volatile and non-volatile memory. We demonstrate these capabilities in self-partitioning grippers, multimodal/color robots and reprogrammable guidewires that perform multi-step or adaptive tasks without external circuitry. By encoding actuation modes, deformation sequences, and memory in a single parameter, this approach establishes a paradigm of material-encoded programmability and points toward monolithic soft robots and reconfigurable structures.