Hygrostack: How to morph under a large load

Morphing matter based on stimuli-responsive materials typically use a bilayer architecture to amplify displacement by leveraging curved geometry. Under a relatively heavy external load, the performance of this architecture declines because much of the deformation shifts from bending to stretching, rendering the bilayer architecture ineffective. Here, we present a tri-layer architecture, termed 'hygrostack.' With a careful choice of layer thicknesses and elastic moduli, this configuration significantly favors bending over stretching response, thereby maintaining the morphing performance of the hygromorph under high loads. Our experiments demonstrate approximately 50-fold increase in displacement using a hygrostack, relative to a bilayer architecture under the same loading conditions. We will present use cases in mechanical actuation and energy harvesting, where the hygrostack architecture leads to substantial improvements in performance. The hygrostack architecture provides a generalizable and easy-to-implement method to enhance the mechanical performance of morphing matter.