'Metamaterial' can switch from soft to hard - and back again

Why not both?

University of Michigan researchers have developed a technique for a new 'metamaterial' that can change its level of solidness, but without damaging or changing the material itself. Metamaterials are man-made materials whose properties come from the way it's constructed rather than what it's composed from. Scientist can then tinker with its structure to affect its properties. Those effects can be very broad: researchers were able to create a camera that doesn't require a lens to work using different man-made materials. This one's different again.

This time, researchers in Michigan have made something that can be easily manipulated to increase the stiffness of its surface, and the difference could be significant: the researchers say it's comparable to the difference between rubber and steel. Even better, because the property comes from the total structure, shifting between hard and soft states doesn't damage the material.

It's all to do with structural hinges inside the metamaterial which, as any sensible group of scientists would (or should), they decided to macro-model from a kids' toy -- some K'nex:

This demonstrates what's happening inside the material: depending on the forces that come in touch with the sides (and how the material is constructed, or its "topological polarization"), it'll give or it won't. The unusual hinges within the metamaterial are what gives it this unusual property -- you can watch the whole, slightly confusing, video here, hosted by Nature.

Xiaoming Mao, Assistant Professor of Physics, says the way an object comes in contact with the edge of the metamaterial changes the geometry of the material's structure, and how it responds to stress at the edge. Because this all happens at the surface, the inside of the metamaterial remains damage-free. The team suggests cars or rocket launch systems as possible future uses, helping to absorb damage from collisions and crashes. It could even prove useful for bicycle tires that self-adjust depending on the surface you're riding on. It certainly won't look like a bunch of K'nex at that point.