⚡ Materials that crawl and dig on their own

The materials we use every day, like steel or rubber, are passive: they only react under the effect of an external force. But there is a different class, called "active matter," which draws on its own energy to move, deform, or respond to pressures.

You can find it in nature, for example, schools of fish that undulate by coordinating their movements, or living cells that reorganize without a conductor.


In their laboratory, researchers from the universities of Amsterdam, New South Wales, and Cambridge have fabricated active materials from rods, rubber bands, and small motors. These systems exhibit unusual properties. For example, a chain of rods connected by motors, instead of bending once under pressure, begins to oscillate continuously. According to the scientists, this repeated movement resembles a form of locomotion like that of reptiles, a walk, or even digging.

Another result surprised the team even more. By building a two-dimensional network with the same building blocks, they observed that making each element more active could make the whole less active. This is the opposite of what Le Chatelier's principle states, which says that small-scale behavior is reflected at large scale. The researchers explain this paradox by a percolation phenomenon: if components are too dense, they block the propagation of elasticity.



Details of this work have been published in two journals. The first study, published in Proceedings of the National Academy of Sciences, shows how active chains can move. The second, accepted at Physical Review X, details the breakdown of Le Chatelier's principle. The researchers believe these discoveries could help design autonomous materials, especially for soft robotics, where flexible robots would act without a centralized control system.

In the meantime, these "bizarre" materials remind us that even the most solid laws of physics can be circumvented when you add a bit of internal energy.