Researchers have developed a polymer structure shaped like a 'Chinese lantern' that can quickly change into more than a dozen curved, three-dimensional forms when it is compressed or twisted. This transformation can be triggered and controlled remotely with a magnetic field, opening possibilities for a wide range of practical uses.

Folds into a round, lantern-like shape

To build the lantern, the team began with a thin polymer sheet cut into a diamond-shaped parallelogram. They then sliced a series of evenly spaced lines through the centre of the sheet, forming parallel ribbons connected by solid strips of material at the top and bottom. When the ends of these top and bottom strips are joined, the sheet naturally folds into a round, lantern-like shape.

The basic lantern object is made by cutting a polymer sheet into a diamond-like parallelogram shape, then cutting a row of parallel lines across the centre of each sheet. This creates a row of identical ribbons that is connected by a solid strip of material at the top and bottom of the sheet. By connecting the left and right ends of the solid strips at top and bottom, the polymer sheet forms a three-dimensional shape resembling a roughly spherical Chinese lantern. Image: Yaoye Hong, NC State University. 

"This basic shape is, by itself, bistable," said Jie Yin, corresponding author of a paper on the work and a professor of mechanical and aerospace engineering at North Carolina State University.

"In other words, it has two stable forms. It is stable in its lantern shape, of course. But if you compress the structure, pushing down from the top, it will slowly begin to deform until it reaches a critical point, at which point it snaps into a second stable shape that resembles a spinning top. In the spinning-top shape, the structure has stored all of the energy you used to compress it.

"So, once you begin to pull up on the structure, you will reach a point where all of that energy is released at once, causing it to snap back into the lantern shape very quickly."

Could create many additional shapes

"We found that we could create many additional shapes by applying a twist to the shape, by folding the solid strips at the top or bottom of the lantern in or out, or any combination of those things," said Yaoye Hong, first author of the paper and a former PhD student at NC State who is now a postdoctoral researcher at the University of Pennsylvania.

"Each of these variations is also multistable. Some can snap back and forth between two stable states. One has four stable states, depending on whether you're compressing the structure, twisting the structure, or compressing and twisting the structure simultaneously."

The researchers also gave the lanterns magnetic control by attaching a thin magnetic film to the bottom strip. This allowed them to remotely twist or compress the structures using a magnetic field.

They demonstrated several possible uses for the design, including a gentle magnetic gripper that can catch and release fish without harm, a flow-control filter that opens and closes underwater, and a compact shape that suddenly extends upward to reopen a collapsed tube. A video of the experiment is available below.