US team uses light to control origami structures

Researchers from North Carolina State University have used different wavelengths of light to control how polymer origami structures fold on themselves.

Described in the journal Science Advances, the work involves using a variety of coloured inks on different hinges of the structures. Because different colours absorb light in their own way, the North Carolina team was able to control the sequence of folding using a range of wavelengths.

“A longstanding challenge in the field has been finding a way to control the sequence in which a 2D sheet will fold itself into a 3D object,” said Michael Dickey, a professor of chemical and biomolecular engineering at NC State and co-corresponding author of the paper.

“And as anyone who has done origami – or folded their laundry – can tell you, the order in which you make the folds can be extremely important.”

As an example, if one hinge is printed in yellow and another hinge is printed in blue, it’s possible to make the yellow hinge fold using blue light. As blue ink doesn’t absorb blue light, the blue hinge won’t fold. However, by subsequently exposing the sheet to red light, the blue hinge can then be activated.

On top of this, the researchers were able to develop structures that folded sequentially under a single wavelength of light. This is due to fact that some colours will absorb a wavelength more efficiently than others, thereby folding more quickly.

“This is a proof-of-concept paper, but it opens the door to a range of potential applications using a simple and inexpensive process,” said Dickey.

“Ultimately, people are interested in self-assembling structures for multiple reasons, from shipping things in a flat package and having them assemble on site to having devices self-assemble in ‘clean’ environments for medical or electronic applications.”