Self-Folding Graphene Machines

Self-folding machines made from graphene oxide paper are inspiring some researchers to dream of a future with real-life Transformers and autonomous search-and-rescue robots.

Many large engineering hurdles stand between humanity and an origami Optimus Prime, but the researchers who developed the new machines say that their innovations could find more immediate uses in sensors, artificial muscles, and wearable devices.

Researchers led by Hongzhi Wang and Qinghong Zhang at Donghua University were inspired by the idea of melding the ancient art of origami with modern materials, a recent trend in flexible device research. But the team wanted to push the field a step further.

“We thought it would be more interesting to make an origami device that not only folds itself but also moves on its own,” Wang says. To do this, the team developed a graphene oxide “paper” that controllably folds, allowing the team to make devices that can bend, grab, or walk (Sci. Adv. 2015, DOI: 10.1126/sciadv.1500533).

The researchers start with two different solutions of graphene oxide flakes: One contains bare flakes, and the other contains flakes coated with polydopamine. The researchers filter the solutions to snag the flakes and build up macroscopic graphene oxide sheets. With each solution, the researchers block different parts of the filter to control where bare and protected materials accumulate.

The team then exposes a sheet to hydriodic acid to reduce the bare graphene oxide, which becomes hydrophobic. The protected graphene oxide, however, remains hydrophilic. Different regions of the same sheet will thus repel or absorb water vapor in the air, creating a strain on the paper that can cause it to fold. That strain can be amplified by heat from an IR laser.

Researchers have been working on similar polymer-based devices for years, but Wang says that the new machines are more mechanically robust.

The graphene oxide machines are also more nimble and maneuverable than most of their polymer predecessors, says Jesse L. Silverberg, a physicist with the Wyss Institute at Harvard University who was not involved with the study. “This opens up a lot of new possibilities,” he says.