Is It a Material? Is It a Robot? It's Both!

Andrew Corselli

Researchers control the metabot’s shape and motion using a magnetic field. (Image: Aaron Nathans, videos by Aaron Nathans and Konstantinos Manos)

In an experiment reminiscent of the “Transformers” movie franchise, engineers at Princeton University have created a type of material that can expand, assume new shapes, move, and follow electromagnetic commands like a remotely controlled robot even though it lacks any motor or internal gears.

“You can transform between a material and a robot, and it is controllable with an external magnetic field,” said researcher Glaucio Paulino, the Margareta Engman Augustine Professor of Engineering at Princeton.

In an article published in the journal Nature, the researchers describe how they drew inspiration from the folding art of origami to create a structure that blurs the lines between robotics and materials. The invention is a metamaterial, which is a material engineered to feature new and unusual properties that depend on the material’s physical structure rather than its chemical composition.

In this case, the researchers built their metamaterial using a combination of simple plastics and custom-made magnetic composites. Using a magnetic field, the researchers changed the metamaterial’s structure, causing it to expand, move, and deform in different directions, all remotely without touching the metamaterial.

The team called their creation a “metabot” — a metamaterial that can shift its shape and move.

The metabot is a modular conglomeration of many reconfigurable unit cells that are mirror images of each other. This mirroring, called chirality, allows for complex behavior. Tuo Zhao, Postdoctoral Researcher in Paulino’s lab, said the metabot can make large contortions — twisting, contracting and shrinking — in response to a simple push.

Here is an exclusive Tech Briefs interview, edited for length and clarity, with Zhao.

Tech Briefs: What was the biggest technical challenge you faced while developing the metabot?

Zhao: The motivation came from origami — our main idea was using origami to serve as ta unit cell. This has been tried before, but not with metamaterials. There was a twisting angle of only about 3 degrees. And then if you look at the vertical deformation, the shrinkage was about 2 percent. So, what we are working on, especially with this origami inspiration, is to extend this to a large multimodal deformation.

We found that our assembly can twist, contract, and shrink with large deformations. Our assembly can twist between zero and 90 degrees, the impact compression is under 25 percent, and the height shrinkage is more than 50 percent. So, basically, this is the key idea of this deformation.

Another interesting aspect we investigated is that we can have two separate actuation schemes.

Tech Briefs: What was the catalyst for this project? How'd the work come about?

Zhao: We were already focusing on this during our last study — that was essentially a 1D robot, but in this work, we are thinking more about how to can utilize this for a 3D assembly and then to make this 3D structure behave like a robot. Then we figured out, because of this special multimodal deformation, we can make a 3D transformer. We put this assembly into a magnetic field. Using a coil system, we can actuate the deformation without any touch. Then, we could show not only the deformation, but also some basic locomotion, for example, moving forward, backward, and steering left and right.

Tech Briefs: Can you explain in simple terms how the chirality works?

Zhao: Chirality is a very important concept explored in many fields, like biology and our DNA. For example, our left and right hands are examples of chirality. So, for our origami system, we have two unit cells combined, which have the same geometry but different chirality. The implication of that is that the two cells can twist in different directions.

Tech Briefs: Do you have any set plans for further research work, et cetera? And if not, what are your next steps? Where do you go from here?

Zhao: What we are mainly working on now is to investigate the stability of this assembly. In the paper, we only show a three-by-three-by-three assembly to demonstrate the structure. But we think, because origami is theoretically scalable, the same concept can be extended to, say, thousands or ten thousands, even millions of unit cells, and it will still work. But the challenge is the fabrication.

So, what we are doing now is we are trying to miniaturize the unit cell at a micro or nanoscale. Along those lines, we have tried two different prototypes. One is a unit cell with a height of two millimeters and the other with a height of 100 microns.