Metamorphic polymer assumes 12 forms

Robotics

Technological Innovation Website Editorial Team - 04/11/2025

It is a simple structure, but manipulating the ribbons transforms the polymer sheet into a mechanical metamaterial. [Image: Yaoye Hong et al. - 10.1038/s41563-025-02370-z]

Polymer with superpowers

Assuming more than a dozen different curved and three-dimensional shapes, simply by compressing or twisting its original structure, would already be a superpower desired by any polymer.

But this new metamorphic polymer also has the advantage that its shape changes can be operated remotely, controlled by means of a magnetic field, allowing the structure to be used for a variety of applications.

Still without its superhero cape, the material is created by cutting a sheet of polymer into a parallelogram shape, similar to a diamond. Then, this sheet receives a series of other cuts, forming parallel lines in the center of each sheet. This creates a row of identical strips connected by a solid strip of material at the top and bottom of the sheet.

When the left and right ends of the solid strips are connected at their top and bottom, the polymer sheet takes on an approximately spherical three-dimensional shape, similar to a Chinese lantern. That's where the polymer gains its cape of superpowers.

"This basic form is, in itself, bistable," explains Jie Yin of North Carolina State University in the US. "In other words, it has two stable forms. It's stable in its lantern form, of course. But if you compress the structure, pushing it from top to bottom, it will begin to slowly deform until it reaches a critical point, at which point it snaps into a second stable form that resembles a spinning top. In the spinning top form, the structure has stored all the energy you used to compress it. So, when you start pulling the structure upwards, it will reach a point where all that energy is released at once, causing it to revert to the lantern form very quickly."

Demonstrations of applications of metamorphic superpolymer. [Image: Yaoye Hong et al. - 10.1038/s41563-025-02370-z]

Metamorphic

But it's not just lanterns and spinning tops. By twisting or folding the strips, either at the top or bottom, including combinations of these manipulations, it becomes possible to create a series of other shapes, each with its own stable "locking" points.

"Each of these variations is also multi-stable. Some can alternate between two stable states. One of them has four stable states, depending on whether you are compressing the structure, twisting the structure, or compressing and twisting the structure simultaneously," Yin added.

Finally, the researcher had the idea of ​​attaching magnetic films to the strips, which opened up the possibility of compressing or twisting the structures remotely, using an external magnetic field.

The team demonstrated several application possibilities, developed by exploring the interlocking of two stable forms. The first is a soft, precise, and delicate robotic gripper, so much so that it was tested by grasping fish in an aquarium. Another is a tap that opens and closes to control the flow of water. Finally, a compact form rapidly expands into a tall form, opening a collapsed pipe.

"In the future, these flashlight units could be assembled into 2D and 3D architectures for a wide range of applications, in shape-shifting mechanical metamaterials and robotics," said Yin. "We're going to explore that."

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