Japanese paper cutting art improves flexible electronics

The stretchable conductors that have been produced so far are either not very flexible or not very conductible. Researchers at the University of Michigan looked to Kirigami, an ancient Japanese paper cutting art to tackle one of the most challenging problems in current electronics research.

It was a truly multidisciplinary approach: Researchers at the University of Michigan looked to Kirigami, an ancient Japanese paper cutting art to tackle one of the most challenging problems in current electronics research. Flexible electronics hold great promise for a variety of new products that can be integrated into many every-day objects, including wearable electronics, flexible plasma-screen displays and, eventually, solar panels that can bend to follow sunlight. But so far, stretchable conductors have been difficult to design. The stretchable conductors that have been produced so far are either not very flexible or not very conductible.

When conductive materials get stretched, they often tear in multiple places, which reduces their ability to conduct electrical impulses. The researchers from the Kotov Lab at the University of Michigan used kirigami, a paper art form that is related to origami but uses cuts in addition to folding, to increase the flexibility of the material.

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To design flexible conductors, researchers usually combine materials with elastic and conductive characteristics, such as polymers and carbon nanotubes. Since the composites consist of flexible and brittle material, they would usually develop micro-rips and lose a high percentage of their initial conductivity when stretched beyond 5 % of their original dimensions.

The scientists at the University of Michigan used photolithography to make a series of strategically placed cuts in a variety of new composite materials, just like a kirigami paper artist would do. They found that they could stretch the material up to 370 % without changing the conductivity.

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“The unique properties of kirigami nanocomposites as plasma electrodes open up a wide range of novel technological solutions for stretchable electronics and optoelectronic devices, among other application possibilities,” write the scientists in their article in Nature Materials.

The idea for this work came from more than a decade of collaboration between paper artist Matt Shlian and materials scientist Max Shtein, both of the University of Michigan at Ann Arbor and co-authors on the new study. The first prototype of the kirigami stretchable conductor was tracing paper covered in carbon nanotubes. The layout was simple, with cuts like rows of dashes that opened to resemble a cheese grater.

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When the prototype showed promising characteristics, they were further explored in computer simulations trying to predict the behavior of the material when the lengths or patterns of the cuts changed. In a next step, the scientists tried a different, more advanced material: They used a special paper made of graphene oxide, a material composed of carbon and oxygen just one atom thick. The material was layered with flexible plastic containing up to 30 layers of each material.

The technology is still far away from being used in actual electronic devices and needs to be tested and developed further but it shows great potential for improving the characteristics of flexible electronics. In the future, people may be able to roll up their electronic devices and to wear their cellphones on their sleeves – literally.

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