Israeli Scientists Develop 'Soft Robot' Metamaterial

Imagine a prosthesis that never chafes, made of programmable material.

To demonstrate that any pattern can be produced on a cube's surface, the researchers developed a cube of 10x10x10 blocks on which a smiley appears when the cube is compressed.
Corentin Coulais

Imagine a prosthesis that never chafes and fits your stump like a glove. A team of scientists working in Tel Aviv and the Netherlands have developed a method to build programmable metamaterial, with the potential to change not only life for the disabled but the entire field of wearable technology and soft robotics.

"Programmable 'machine materials' could be ideal for prostheses or wearable technology in which a close fit with the body is important," says Dr. Yair Shokef of TAU’s School of Mechanical Engineering. "If we can make the building blocks more complex or produce these from other materials, then the possibilities really are endless."

The team proved their concept by printing of a metamaterial cube using a 3-D printer. (WATCH:) A smiley-face pattern emerged on the side of the cube when it was compressed between appropriately patterned surfaces.

Metamaterial in action YouTube

Ordinary material, from your computer monitor to your coffee to your cat, consists of atoms and molecules. The state of the material (solid, liquid, gaseous, etc.) and its behavior (electricity conduction, hardness for instance) are determined by their chemical composition, Shokef explains to Haaretz.

A metamaterial is a material engineered by man, constructed of units bigger than atoms or molecules, whose state and behavior is determined by the characteristics of the units, not the chemical composition.

"The entire material is made of the same elementary materials [molecules, atoms] but the building blocks are bigger in scale – nanometers, or even millimeters or centimeters. We artificially create a structure consisting of such blocks and the characteristics are determined by geometrical structure," Shokef explains.

Take for instance an ordinary diamond. Its component particles are carbon atoms arranged in a specific structure, at atomic scale (10-10m). "In metamaterials, the objects repeating themselves are geometrical structures at a much bigger scale," he says.

Dr. Yair Shokef.
Courtesy of Tel Aviv University  

Now the punchline: When you plan the material using big units on a large scale, not atoms, you have more ability to control the "crystalline" arrangement and theoretically, we can control the substance's physical characteristics. Thus the 3-D printer smiley metamaterial test.

That specific metamaterial was programmed for the application of spatially patterned compression in one direction to cause a programmed spatially patterned deformation (dents and protrusions) in other directions. “On a seemingly normal cube, a programmable pattern of bulges appears when it is compressed,” said Dr. Shokef. “In the case of metamaterials, those designed by humans, the spatial structure determines the material's behavior.”

The mechanical metamaterial is described in the paper "Combinatorial Design of Textured Mechanical Metamaterials" published this week in Nature by Corentin Coulais, Eial Teomy, Koen de Reus, Yair Shokef and Martin van Hecke.

One intriguing application of metamaterials, irrespective of the above work, is efforts to create "invisibility" cloaks a-la Star Trek, by monkeying with the way the material reacts to light. "Invisibility" metamaterials control and direct the propagation and travel of specific light waves, resulting in seeming invisibility. Which doesn't mean you can't stub your toe on the object. You just don't see it because the light waves are being guided around them without being affected by the object itself.

Star Trek: Sneaky Romulans use a cloaking device. YouTube