Origami-inspired graphene paper that can fold itself could be used to create anything from miniature robots to artificial muscles, according to a new study.
Scientists from Donghua University in China have demonstrated that gently heating a sheet of graphene paper, which is extraordinarily strong - about 200 times stronger than steel by weight, could make it fold into a device that is able to walk forward and backward. And, in a first for this kind of self-folding material, they showed it could also change directions.
The research could help scientists develop self-folding structures and devices for modern applications, including wirelessly controlled micro robots, artificial muscles and devices for tissue engineering, said Jiuke Mu, a Ph.D. student at Donghua University and one of the material’s inventors.
The technology relies on specially treating sections of graphene paper so that they naturally absorb water vapor from the atmosphere, the researchers said. When the paper is heated, this water is released, causing those sections to shrink and bend. When the heating stops, this process is reversed.
Careful placement of these treated sections made it possible to create various self-folding objects, including the walking device, a self-assembling box and an artificial hand that can grasp and hold objects five times heavier than itself.
The researchers determined the 3D shape into which the paper folds simply by altering the placement and width of the specially treated areas, with wider sections bending more than narrower ones.
The caterpillarlike walking device was created by building a rectangular sheet of graphene paper with three treated bands running across it that got progressively wider from front to back. When the sheet was lit with a near-infrared light, the bending of these sections caused the sheet to curve into an arch.
But the varying widths of these sections meant the rear of the sheet curved more than the front, so when the light was switched off and the sheet relaxed, the device stretched forwards. The response of the material was so quick that five of these steps took only 2 seconds. By heating just one side of the sheet, the researchers were also able to make the device turn, because one side would bend more than the other.
Self-folding materials have become a major topic of research in recent years, with particular focus on so-called active polymers, materials that convert other forms of energy into mechanical work. But studies to date have often relied on electrical circuitry, unusual environmental conditions or complicated combinations of materials, which tend to be fragile.
In addition to having the potential to inspire self-folding devices, the researchers said graphene paper could eventually be used to create artificial muscles. The stress generated by one of the paper devices was nearly two orders of magnitude higher than that of mammalian skeletal muscles, the researchers said.
