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.

This work establishes a means to exploit genetic networks to create living synthetic composites that change shape in response to specific biochemical or physical stimuli. Baker’s yeast embedded in a hydrogel forms a responsive material where cellular proliferation leads to a controllable increase in the composite volume of up to 400%. Genetic manipulation of the yeast enables composites where volume change on exposure to l-histidine is 14× higher than volume change when exposed to d-histidine or other amino acids. By encoding an optogenetic switch into the yeast, spatiotemporally controlled shape change is induced with pulses of dim blue light (2.7 mW/cm2). These living, shape-changing materials may enable sensors or medical devices that respond to highly specific cues found within a biological milieu.

Engineered living materials integrate genetic engineering and synthetic materials to program stimuli responses that enable the fabrication of devices for diverse applications.