Imagine this: With a simple flash of light or heat, an unassuming piece of paper folds itself into a crane and, as the light pulses, flaps its paper wings in flight. Though the concept is still in its early days, scientists are closer to making this a reality with the recent unveiling of a graphene-based self-folding paper.
The new origami-inspired paper can’t exactly fly away. But scientists have successfully "programmed" it to fold itself into a box and to walk inchworm-style. They even created a jointed hand out of the paper that can grasp and hold an object five times its own weight, according to the study published last week in the journal Science Advances.
"We thought it would be more interesting that an origami device not only folds itself but also can move on its own, like an origami crane can fly or an origami dragon can walk," Hongzhi Wang, an author of the paper and materials scientist at Donghua University in Shanghai, China, writes in an email.
Scientists constructed this self-folding paper by layering two types of graphene—one that holds moisture and one that doesn't. The paper that absorbs moisture from the air can rapidly dehydrate under flashes of infrared light or heat, which causes it to contract. So by strategically positioning layers of this paper in the model, the scientists created joints or hinges.
With the lights on, the paper bends. With the lights off, the paper flattens. This simple, fast and reversible process can be repeated over multiple cycles without the paper breaking down. To make the paper turn a corner, the scientists just reposition the light or heat source.
Wang and his team have high hopes for their tiny tech, calling it the "embryo of a novel kind of robot." The paper could be incorporated into the burgeoning field of microrobots, artificial muscles and tissue engineering. There is also a potential application in solar technology, to create self-folding solar panels.
"In the near future, it even could bring changes to people's life," writes Wang. "For example, smart clothes could change their shape and style in response to body temperature, environmental changes or other gentle simulations."
This isn’t the first self-folding or walking material. Polymers have been the main focus of previous efforts, but these shape-memory polymers, crystalline polymers and gels have their limitations. They are unstable in extreme conditions, expensive and restricted in the shapes they can create.
"Compared with the traditional active materials, the structure of this paper is simpler, the response is faster, the output is more efficient," Wang writes.
For now, Wang and his team are working to make the system even more efficient and scale the paper down, shooting for a nano-sized all-graphene origami device.