A New String Theory of Metamaterials

As technology continues to advance and we redefine what is possible, a number of subfields have to come together to produce big innovations. For example, as more capable flexible electronic components are developed, we will need to create soft and flexible bodies to produce the practical soft robots of tomorrow. Similarly, long-distance human space travel is not only about bigger and better rockets — we will also need ways to pack more, and lighter, supplies into compact spaces to support the mission.

A crucial, yet often overlooked, component of these new technologies is the materials that they are made from. Traditional metals, plastics, and so on, simply cannot support every present and future use case. Researchers at the University of California, Los Angeles have put forward a new option that makes a lot of sense where versatility is required. Inspired by push puppet toys, their metamaterial can form a rigid, preprogrammed shape, it can collapse into a pile of nothingness, or assume a form anywhere in between. And the state of the material can be adjusted to no end.

The novel material takes the form of small beads, each of which has a convex and concave side. This design enables pairs of nearby beads to tightly interlock when these features are mated together. Much like a push puppet, the beads have a hollow core that allows them to be threaded onto a cord. When that cord is pulled taut, the beads interlock with one another, forming a stiff structure. But if the cord is loosened, either manually or with an actuator, the structure will either completely disassemble or take some intermediate form, depending on the degree of loosening.

Experiments with a cube-like lattice of beads demonstrated that by tightening the cords to different levels, the impact of a ball being dropped on top of the structure could be dampened to varying degrees. A fully-stiffened structure barely budged, whereas a softer structure could absorb more of the impact and cradle the ball. And when the job was finished, the entire structure collapsed into a small space.

The researchers see opportunities for their metamaterial to be used for many applications, such as in self-assembling shelters, soft robot bodies, and in equipment for space missions that must be stored compactly. Toward that goal, they plan to further experiment with different types and shapes of beads, as well as methods of connecting them, to fine-tune their approach for real-world use.