Over the past 20 years, scientists are developing metamaterials, or materials that don’t occur naturally and whose mechanical properties result from their designed structure instead of their chemical composition. They permit researchers to make materials with specific properties & shapes. Metamaterials are still not widely-used in everyday objects, but that would soon change. Tian Chen, a post-doctoral at 2 EPFL labs, the Flexible Structures Laboratory, headed by Pedro Reis, and therefore the Geometric Computing Laboratory, headed by Mark Pauly, has taken metamaterials one step further, developing one whose mechanical properties might often re-programmed after the material has been made. His research published in Nature.
A single material with several mechanical functions
“I wondered if there was how to vary the interior geometry of a material’s structure after it’s been created,” says Chen. “The idea was to develop a material which will display a variety of physical properties, like stiffness & strength, in order that materials don’t need to get replaced each time. For instance, once you twist your ankle, you initially have to wear a stiff splint to hold the ankle in place. Then as it heals, you’ll switch to a more flexible one. Today you’ve to exchange the whole splint, but the hope is that at some day, one material can serve both functions.”
Silicon and magnetic powder
Chen’s metamaterial is made from silicon & magnetic powder and features a complicated structure that permits mechanical properties to vary. Each cell within the structure behaves like an electrical switch. “You can activate & deactivate individual cells by applying a magnetic field. That modifies the interior-state of the metamaterial and consequently, its mechanical properties,” says Chen. He explains that his programmable material is analogous to computer devices such as hard drives. These devices contain bits of data which will be written to & skim from in real time. The cells in his programmable metamaterial called m-bits, work just like the bits in a disk drive, they will be switched on, making the material stiffer, or off, making it more flexible. And researchers can program various combinations of on & off to give the material precisely the mechanical properties they require at any given time.
To develop his material, Chen drew on methods from both computer science & mechanical engineering. “That’s what makes his project so-special,” says Pauly. Chen also spent a considerable amount of time testing his material in each-of its different states. He found that it could indeed be programmed to achieve various degrees of stiffness, deformation & strength.
Many research horizons
Programmable metamaterials are akin-to machines, like robots, that employ complicated, energy intensive electronic mechanisms. With his research, Chen aims to find out the proper balance between static materials & machines. Reis sees tons of potential for further research using Chen’s technology. “We could design a way for creating 3D structures, since what we’ve done thus far is merely in 2D,” Reis says. “Or we could shrink the scale to form even smaller metamaterials.” Chen’s discovery marks a fundamental step forward, because it is the first-time scientists have developed a truly reprogrammable mechanical metamaterial. It exposes many exciting avenues for research & cutting-edge industrial applications.
