Topological metamaterial: From hard to soft and back again

A material has many qualities. It can be light or heavy, translucent or not, hard or soft, etcetera. Often, these properties cannot be changed. However, with metamaterials, materials that depend on their structure rather than what they are made of, the structure can be tweaked to suit your purpose. Researchers at the University of Michigan have created a topological metamaterial that allows the material to switch between being hard as steel and soft as rubber.

The researchers discovered a way to compose a metamaterial that can be easily manipulated to increase the stiffness of its surface by orders of magnitude— the difference between rubber and steel. These properties are “topologically protected”, which means that the material’s properties come from its total structure. They are easily maintained even as the material shifts repeatedly between its hard and soft states.

The way an object comes in contact with the edge of the metamaterial changes the geometry of the material’s structure, and therefore how the material responds to stress at the edge. But metamaterial’s topological protection allows the inside of the metamaterial remains damage free.

The new design could, for instance, pave the way for rockets that stay rigid as they take off and become softer when they come into land, or for car steering wheels made to absorb pressure in a crash, to protect the passengers inside. Another use of this metamaterial could be in bicycle tires that change hardness depending on the ground.

The University of Michigan researchers demonstrate the topological metamaterial using the K’Nex construction system in the video below.