Three-dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual thiol-ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo-responsive structures that sequentially and reversibly undergo multiple shape changes.

Soft actuators that undergo programmable shape change in response to a stimulus are enabling components of future soft robots and other soft machines. Strategies to power these actuators often require the incorporation of rigid, electrically conductive materials into the soft actuator, thus limiting the compliance and shape change of the material. In this study, we develop a 4D-printable composite composed of liquid crystal elastomer (LCE) matrix with dispersed droplets of eutectic gallium indium alloy (EGaIn). Using deformable EGaIn droplets in place of rigid conductive fillers preserves the compliance and shape-morphing properties of the LCE. The process enables 4D-printed LCE actuators capable of photothermal and electrothermal actuation. At low liquid metal (LM) concentrations (71 wt %), the composite actuator exhibits a photothermal response upon irradiation of near-IR light. Printed actuators with a twisted nematic configuration are capable of bending angles of 150° at 800 mW cm–2. At higher LM concentrations (88 wt %), the embedded LM droplets can form percolating networks that conduct electricity and enable electrical Joule heating of the LCE. Actuation strain ranging from 5 to 12% is controlled by the amount of electrical power that is delivered to the composite. We also introduce a method for multimaterial printing of monolithic structures where the LM filler loading is spatially varied. These multifunctional materials exhibit innate responsivity where the actuator behaves as an electrical switch and can report one of two states (on/off). These multiresponsive, 4D-printable composites enable multifunctional, mechanically active structures that can be powered with IR light or low DC voltages.

Shape-switching behavior,w here at ransient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus,iscritical to building smart structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D-print shape-switching liquid crystalline elastomers (LCEs) functionalizedw ith supramolecular crosslinks, dynamic covalent crosslinks,a nd azobenzene.T he salient property of shape-switching LCEs is that light induces longlived, deformation that can be recovered on-demand by heating.U V-light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks,r esulting in ap rogrammed deformation. After UV,t he shapeswitching LCEs fix more than 90 %o ft he deformation over 3daysb yt he reformed supramolecular crosslinks.U sing the shape-switching properties,weprint Braille-like actuators that can be photoswitched to displaydifferent letters.This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.

Shape-switching behavior,w here at ransient stimulus induces an indefinitely stable deformation that can be recovered on exposure to another transient stimulus,iscritical to building smart structures from responsive polymers as continue power is not needed to maintain deformations. Herein, we 4D-print shape-switching liquid crystalline elastomers (LCEs) functionalizedw ith supramolecular crosslinks, dynamic covalent crosslinks,a nd azobenzene.T he salient property of shape-switching LCEs is that light induces longlived, deformation that can be recovered on-demand by heating.U V-light isomerizes azobenzene from trans to cis, and temporarily breaks the supramolecular crosslinks,r esulting in ap rogrammed deformation. After UV,t he shapeswitching LCEs fix more than 90 %o ft he deformation over 3daysb yt he reformed supramolecular crosslinks.U sing the shape-switching properties,weprint Braille-like actuators that can be photoswitched to displaydifferent letters.This new class of photoswitchable actuators may impact applications such as deployable devices where continuous application of power is impractical.