Expansion mechanics of hydrogel-driven metamaterials with multiple deformation modes

Hydrogel is widely employed in flexible electronics and soft robotics as soft mechanical material. Previous reports exploited the swelling properties of hydrogel to achieve large negative deformations, but few reports exhibit multiple deformation modes. This paper designs two-dimensional metamaterials that convert hydrogel swelling deformation into bending deformation, including positive/negative swelling, isotropic/anisotropic, and gradient/bending deformation modes. The regulation of hydrogel swelling on the negative expansion deformation of metamaterials is explored through the theoretical model and finite element analysis. The corresponding relationship between the microstructure deformation and the band gap change during the hydration process is obtained. Inspired by kirigami, we proposed a self-assembly model with substrate expansion-driven three-dimensional microstructure. The results show that the deformation modes of metamaterials may be interconverted through structural design. The band gap can be tuned by swelling deformation.