Katia Bertoldi, Harvard University
Kirigami Inspired-Metamaterials—From Morphable Structures to Soft Robots
Written by Hortense Le Ferrand
Kirigami is a Japanese art form where paper sheets are cut to enable folding resulting in the rise of highly sophisticated three-dimensional structures.
In addition to the transition from two-dimensional to three-dimensional, plastic kirigami with geometrical arrays display interesting mechanical properties that depend on shape of the unit elements: squares, triangles, or trapezes, and on the width and thickness of the ligaments bridging these elements. Typically, the flat kirigami initially deforms in its plane as the ligaments deform. Then, above a predictable critical strain, it enters a buckling unstable mode where the stress plateaus as the single elements pop-up in or out. Stretching further, plastic deformation of the hinges creates a permanent folding rigidifying the structure.
When wrapped around an inflated elongated balloon, kirigami with triangular, circular of trapezoidal-shaped elements pop-up all in the same direction, resulting with an increased friction coefficient in one direction. Kirigami with squares also exhibit pop ups but with isotropic friction coefficient. Katia Bertoldi and her research team thus exploited the anisotropy to induce snakelike motion on the balloon when it is repeatedly inflated and deflated. With control and actuation directly on board, the structure can move by itself. Her team is now investigating how to improve the skin to control the direction and motion of these biomimetic snakes.