Material or Robot? A Shape-Shifting Revolution: Princeton Engineers Develop Metabot Material

Inspired by origami and powered by magnetic fields, a new metamaterial developed at Princeton University blurs the line between robots and materials — expanding, twisting, and moving without motors or gears. Could this groundbreaking invention transform fields from medicine to aerospace?

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 April 23 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 electromagnetic fields carry power and signal at the same time. Each behavior is very simple but when you put them together the behavior can be very complex,” said Minjie Chen, an author of the paper and an associate professor of electrical and computer engineering and Andlinger Center for Energy and the Environment at Princeton. “This research has pushed the boundaries of power electronics by demonstrating that torque can be passed remotely, instantaneously, and precisely over a distance to trigger intricate robotic motions.”

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, a postdoctoral researcher in Paulino’s lab said the metabot can make large contortions — twisting, contracting and shrinking — in response to a simple push.

Xuanhe Zhao, an expert in materials and robotics who was not involved in the research, said the “work opens a new and exciting avenue in origami design and applications.”

“The current work has achieved extremely versatile mechanical metamaterials by controlling the assembly and chiral state of the modules,” said Zhao, the Uncas and Helen Whitaker Professor at MIT. “The versatility and potential functionality of the modular, chiral origami metamaterials are truly impressive.”

Davide Bigoni, a professor of solid and structural mechanics at the Universita’ di Trento in Italy, called the work groundbreaking and said it could “drive a paradigm shift across multiple fields including soft robotics, aerospace engineering, energy absorption, and spontaneous thermoregulation.”

Exploring the technology’s robotics applications, Tuo Zhao, an author of the paper, used a laser lithography machine at the Princeton Materials Institute to create a prototype metabot that was 100 microns in height (a little thicker than a human hair). The researchers said similar robots could one day deliver medicines to specific parts of the body or help surgeons repair damaged bones or tissue.

The researchers also used the metamaterial to create a thermoregulator that works by shifting between a light-absorbing black surface and reflective one. In an experiment, the researchers exposed the metamaterial to bright sunlight and were able to adjust the surface temperature from 27 °C to 70 °C and back again.

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Another possible use lies in applications for antennae, lenses and devices that deal with wavelengths of light.

Geometry holds the key to the new material. The researchers built plastic tubes with supporting struts arranged so the tubes twist when compressed, and compress when twisted. In origami, these tubes are called Kresling patterns. The researchers created the building blocks of their design by connecting two mirror-image Kresling tubes at the base to make one long cylinder. As a result, one end of the cylinder folds when twisted in one direction and the other end folds when twisted in the opposite direction.

This simple pattern of repeating tubes makes it possible to move each section of the tube independently using precisely engineering magnetic fields. The magnetic field causes the Kresling tubes to twist, collapse, or pop open, creating complex behaviors.

Paulino said that one consequence of chirality — the mirror-image sections — is that the material can defy the typical rules of actions and reactions in physical objects. “Usually, if I twist a rubber-beam clockwise and then counter-clockwise, it returns to its starting point.” Paulino said. The group created a simple metabot that collapses when twisted clockwise, then reopens when twisted counterclockwise — a normal behavior. However, if twisted in the opposite sequence — counterclockwise then clockwise — the same device collapses, then collapses further.

Paulino said this asymmetrical behavior simulates a phenomenon called hysteresis, in which a system’s response to a stimulus depends on the history of changes within the system. Such systems, which are found in engineering, physics and economics, are difficult to model mathematically. Paulino said the metamaterial offers a way to directly simulate these systems.

A more distant use for the new material would be to design physical structures that mimic the performance of logic gates made with transistors in a computer.

“This gives us a physical method to simulate complex behavior, such as non-commutative states” Paulino said.

Original Article: The article, “Modular chiral origami metamaterials,” was published April 23 in Nature.

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