Traveling kinks in viscoelastic kirigami

Mechanical waves without inertia are functional mechanisms often found in nature yet remain rare in synthetic materials—so far, they only exist in active or stimuli-responsive materials. Here, we demonstrate the presence of traveling kinks in purely dissipative metamaterials, and we show that they can be used for sensing applications, dynamic pattern morphing, and transport of objects. To do this, we use multitexture kirigami with suitably patterned viscoelastic properties that buckle in different styles depending on the loading rate. At long timescales, viscoelastic relaxation triggers a snapping instability governed by geometrical nonlinearities and viscoelastic properties of kirigami unit cells. When multiple unit cells are connected into a 1D strip, the snapping instability occurs in sequence, and a traveling overdamped kink emerges. Our 1D model explains such a wave as a reaction-diffusion process similar to overdamped waves in many biological systems. We further demonstrate that such a kink underpins dynamic shape morphing in 2D kirigami and can be used to transport objects. Our results expand the span of nonlinear waves of metamaterials by appending an overdamped regime and open avenues for using highly viscoelastic materials in soft robotics and biomimicry.