The art of folding paper is a generations-old leisure activity that is surprisingly being translated into new technology, like these awesome self-folding origami mini-robots that may someday perform nanosurgery. Now the Japanese art of paper-cutting, or kirigami, may help engineers develop bendable, stretchable and flexible electronics that may someday end up on our clothes, or even in our bodies.
Conventional electronics use materials or are powered by batteries that tend to be inflexible, brittle and rigid. But this is poised to change with new materials like graphene and other electrically conductive composites coming to the fore. Research teams across the world are experimenting with the possibilities of translating paper-cutting techniques into new kinds of transistors and batteries that can bend, twist and deform without affecting overall performance, or potentially increasing battery life.
Bendable Display Screens
One team at the University of Michigan published a study in “Nature Materials” looking at the use of kirigami techniques to increase elasticity of electrically conductive paper composites by making small, precise incisions on them. Creating flexibility in nano-materials can be difficult, due to any number of unpredictable “strain-concentrating defects” and the tendency of nano-components actually stiffening up under high stress.
But kirigami methods of cutting up these materials appears to be one way to bypass these limitations, says Dr. Nicholas Kotov, professor of engineering at the University of Michigan: “Typically the strain [the conductor] can withstand is two percent. But when we put the pattern of Kirigami over that sheet, it turns out we can indeed increase the strain dramatically, by at least a couple of orders.”
The researchers found that the composite sheets, cut with kirigami patterns, could tolerate up to 370 percent more strain than conventional conductor materials, as the tiny cuts would distribute stress over a larger area — something that could be translated into flexible, bendable screens.
Kirigami-Inspired, Graphene-Based Bio-Implants
Scientists at Cornell University are also experimenting with paper-cutting techniques on graphene, a highly conductive carbon-based materials that is only one atom thick. As an alternative to rigid and breakable silicon components, researchers wanted to create transistors with stretchable and deformable electrodes, springs and hinges that might one day appear in elastic electronics, or tiny, bio-compatible implants that move along the body with little discomfort.
In the study published in “Nature,” Cornell researchers describe how they crafted a gold-crowned pyramid by layering small gold pads onto sheets of graphene, and then cut them using lithography techniques. Despite these cuts which allowed the material to stretch to 240 percent of its original size, the electrical conductance remained the same.
The team also made manipulable graphene ‘hinges’ that could link two gold pads together. Both models were surprisingly resilient: the pyramid survived 1,000 deformations before performance was reduced, while the hinges soldiered through 10,000 cycles.
Experiments were done primarily on the micron scale, so that scientists could see what was happening, says team member and nanoscientist Paul McEuen: “All of the experiments were done in water using an optical microscope. If we went to the nanometer scale we wouldn’t be able to see anything.” However, McEuen postulates that smaller, foldable, nano-scaled devices — capable of crossing cellular membranes — could be made with these techniques.
Kirigami-ing the Way to Flexible Batteries for Wearables
Kirigami could potentially pave the way for flexible batteries too, according to another recent study done by Arizona State University and published in “Scientific Reports” and “Nature.” Aiming to combat the short battery life of fixed-size battery cells in smartwatches and fitness trackers, the research team cut up aluminum foil kirigami-style, coated it with a layer of electrically conductive material, and rigged it up to a smartwatch.
They discovered that this flexible, lithium ion battery, which was wrapped around an arm, could stretch up to 150 percent of its original size, without affecting the smartwatch’s video playback performance. It could mean a future where wearable electronics can have bigger, more flexible batteries that offer longer-lasting power, says Dr. Hanqing Jiang, an associate professor who led the team: “The kirigami-based methodology can be readily expanded to other applications to develop highly stretchable devices and thus deeply and broadly impact the field of stretchable and wearable electronics. Other applications may include smart bracelets and smart headbands.”
The trend in technology is to make it increasingly “unobtrusive” in our lives — to make it more of an ambient element rather than a screen or a device that you have stare at or hold in your hands. Technology would almost be invisible, yet present; integrated into our homes, our kitchens, our clothes, our daily habits, even to the point of it anticipating and adapting to our emotional state. Making gadgets flexible may be one way to literally weave new stacks of technology into the fabric of our lives, allowing it to move as needed, and unnoticed.
Images: University of Michigan, Cornell University, Arizona State University.