Shape Programming of Porous Bilayer Hydrogel Structures

Abstract Shape-programmable materials have garnered significant attention for their ability to morph into complex three-dimensional (3D) configurations under external stimuli, with critical applications in the fields of biomedical engineering, soft robotics, and sensing technologies. A current challenge lies in determining the geometric parameters of the initial two-dimensional (2D) structure and the intensity of the external stimulus required to achieve a target 3D shape. In this work, we introduce a novel inverse design strategy based on hole-pattern engineering. Utilizing a temperature-sensitive bilayer hydrogel with differing coefficients of thermal expansion in each layer, we achieve controlled bending deformations by varying the porosity distribution in one of the layers. Drawing on the Timoshenko theory on bimetallic beam, we establish a quantitative relationship between the relative density and curvature, allowing for the hole distribution of the initial structure to be tailored to the desired curvature. We demonstrate the efficacy of our inverse design approach with several prototypical 3D structures, including variable-curvature strip and ellipsoidal surface, validated through finite element simulations and experimental trials. This strategy paves the way for advanced fabrication techniques in developing smart materials and devices with programmable shapes.