Donghua University

Like a robotic inchworm, this flat strip of material reels up and scoots along a lab bench all by itself, turning corners when needed. With other origami-like tricks, the same material rapidly folds itself into a minuscule box, grabs objects, and worms its way through tiny pipes. All this from lightweight, versatile graphene.

A team of Chinese engineers and materials scientists at Donghua University in Shanghai have just devised a fascinating new method to transform sheets of incredibly strong graphene—atom-thin sheets of carbon often hailed as the supermaterial of the future—into self-folding materials with fantastically promising properties. According to Hongzhi Wang, a researcher with the team, the graphene-based material is lightweight, inexpensive to make, "and the fabrication process is very, very simple. Basically any existing chemistry laboratory could make this," he says. The research is published today in the journal Science Advances.

Donghua University

"It's much like how wet paper will wrinkle after it's dried."

"There's two quite impressive aspects of this research that really jumped out at me," says Jesse Silverberg, a physicist who studies folding materials at Harvard, who was not involved in the research. "First, for most self-folding materials, it can often take several minutes up to hours for the material to fold. Here, everything happens in just a few seconds. . . Secondly, with very few exceptions, most of these types of materials must be folded in one simultaneous step, but these [researchers] are able to selectively fold and unfold the graphene," he says. This ability to self-fold in stages opens up —from clever springs to flapping machines—to graphene.

You'd probably never guess by watching it inch across a lab table or crawl through a tube, but Wang's self folding graphene actually works by inhaling and exhaling tiny amounts of water. Wang explains that this is because his material is created by selectively binding together two flavors of graphene. The first is regular graphene oxide. The second is graphene oxide covered with a sponge-like coating called polydopamine (or PDA). This PDA coating makes graphene expand as it soaks up the tiny amounts of moisture naturally in the air, and shrink tight when it's shocked into losing that water. "Much like how wet paper will wrinkle after it's dried," Wang says.

By combining the two materials, designing origami-inspired machines is straightforward. Wang needs only to carefully layer PDA-coated graphene at places where creases and joints in his machines need to be formed. After that, getting the graphene to lose its water and start folding is simple. Heat will do it, but so will a gentle pulse of light. And by directing pinpoint pulses of light, Wang can pick which part of his graphene machines will fold, and when. When the light lets up, the graphene instantly soaks up the insanely small amount of moisture it needs from the ambient air.

Donghua University

By creating fast-folding origami objects that can unfurl, move, and bend in multiple steps, Silverberg says, Wang's material overcomes "several challenges toward building actual transforming robots," he says. Of course, we're still nowhere near Transformers, but graphene's natural properties (strength and chemical stability) make it an ideal starting point for building simple micro-machines.

Wang sees other, even more fascinating opportunities for his lightweight material in the near future. "You can imagine sending a very compacted form of this material into space as part of a satellite. Once up there, it could unfurl and, [because of] graphene's natural photoelectric effects, start harvesting energy from sunlight."

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