Armed with a PowerPoint slide and an ordinary LED projector, scientists have produced self-folding 3-D origami structures from photocurable liquid polymers. The structures, all about a half-inch in size, could have applications in soft robots, microelectronics, soft actuators, mechanical metamaterials and biomedical devices.

It is believed to be the first application to create self-folding origami structures through the control of volume shrinkage during patterned photopolymerization, according to researchers from Georgia Institute of Technology and Peking University. A grayscale pattern of light and dark shapes is projected onto a thin layer of liquid acrylate polymer placed in a plate or between two glass slides. A photoinitiator material mixed into the polymer initiates a crosslinking reaction when struck by light from the LED projector, causing a solid film to form. A light-absorbing dye in the polymer serves as a regulator for the light. Due to the complicated interaction between the evolution of the polymer network and volume shrinkage during photo curing, areas of the polymer that receive less light exhibit more apparent bending behavior.Origami structure created through a self-folding process is shown on a U.S. quarter for size comparison. Image credit: Rob Felt, Georgia Tech

When the newly-created polymer film is removed from the liquid polymer, the stress created in the film by the differential shrinkage causes the folding to begin. To make the most complex origami structures, the researchers shine light onto both sides of the structures.

To make the most complex shapes with bending in both directions, the researchers can flip the patterned film over to create crosslinking on the other side. The process can be delicately tuned by controlling the illumination time and the light intensity, and the method has been used to fabricate microfluidic devices and synthesize microparticles.

The researchers used poly(ethylene glycol) diacrylate in this demonstration, but the technique should work with a broad range of photocurable polymers.