Programmable anisotropic actuation of hydrogel-composite mechanical metamaterials

Abstract Hydrogel actuators hold great potential for soft robotics but suffer from isotropic swelling and low structural rigidity. We propose a composite actuator integrating hydrogels with 3D-printed mechanical metamaterial scaffolds to achieve programmable anisotropic actuation. We investigated two scaffold materials: UV-curable resin and Thermoplastic Polyurethane (TPU). While resin scaffolds provided high interfacial strength, TPU scaffolds demonstrated superior durability, accommodating large swelling deformations without failure. Leveraging the robust TPU composite, we developed cylindrical actuators designed for specific deformation modes. The radial-expansion model successfully achieved diameter increase while suppressing the axial shortening phenomenon typical of conventional stents. This work establishes a design strategy balancing material properties and geometric programming to realize robust, complexly deforming soft actuators.