Kirigami Mechanics Transformed by Cutting Technique

Kirigami is a variation on the Japanese art of origami, or paper folding, whereby cuts are used to create three-dimensional structures. For example, pop-up cards created from a sheet of paper. Kirigami has additional applications in engineering design to make materials with unique mechanical behavior. Although most studies on kirigami materials have focused on structures with parallel and perpendicular cuts, limiting the applications of the final creations.

Now, researchers at The University of Osaka have developed a novel kirigami structure with inclined cuts that can twist when stretched. This design can be harnessed to make soft robots. This exciting discovery is set to be published in Royal Society Open Science.

In engineering, precise cuts can be made in flat sheets to create complex flexible three-dimensional structures that could not be produced using traditional manufacturing techniques. These kirigami materials have unique mechanical properties, such as high strength-to-weight ratios, which arise from their internal structure; as opposed to properties originating from the chemical composition of the base material.

In typical kirigami patterns, cuts are made parallel or perpendicular to the loading direction. However, The University of Osaka team innovated kirigami patterns by making periodic parallel inclined laser cuts in polyester sheets. The sheets were then rolled into cylinders and subjected to mechanical tests.

"We were able to characterize the mechanical properties of these kirigami structures in terms of their chirality," explains lead author, Isamu Hashiguchi. "Chirality is a geometric property - a chiral structure cannot be superimposed on its mirror image."

One common example of chirality includes human hands, which while similar, are not identical and cannot exactly overlay one another. This 'handedness' for materials is important, as it allows for the development of materials with tunable properties - expanding their potential applications.

As part of the mechanical tests completed, the scientists found that stretching the cylindrical sheets caused them to twist and rotate. Thus, the developed structures provide an efficient way to couple tension and rotation, meaning forces exerted along the structure could be converted into a rotational force.

"We found that some chiral kirigami structures are auxetic," reports Ryuichi Tarumi, senior author. "This means that when these structures are stretched longitudinally, they expand laterally instead of becoming thinner."

Auxetic materials find application in medical stents to support expansion of bronchial tubes, the esophagus, or blood vessels. The rotation of kirigami structures under elongation also makes them promising soft twist actuators, flexible robotic components with twisting ability, used for dexterous manipulation.

Fig. 1

Caption: Developed Kirigami structures and their response to stretching.

Credit: Isamu Hashiguchi, Tomoka Nakahara, Kota Fukui, Shunsuke Kobayashi and Ryuichi Tarumi