Active materials that move and adapt could reshape future robotics and engineering

Scientists from the University of Cambridge, working with researchers at the University of Amsterdam and University of New South Wales, are exploring a new class of active materials – materials that use their own internal energy to change shape and behaviour. Unlike conventional materials, which only respond when external forces are applied, these systems can actively adapt, opening new possibilities for robotics and advanced engineering.

When we think of materials, we usually think of substances like metal, concrete, glass or rubber. What these examples have in common is that they are inactive: they move or deform only when external energy is applied.

Another class of materials is made of active matter and behaves differently. These materials contain their own energy and can respond dynamically to forces, much like biological systems like flock of birds behaving as one single entity that responds to external inputs like wind, terrain changes or the presence of food or a natural resting place.

Now, researchers have recreated this behaviour in the lab using simple components like rods, motors, and rubber bands. The study, published in two papers in the Proceedings of the National Academy of Sciences and Physical Review X, shows how by assembling these components into structured systems, scientists have created materials that can generate motion and reorganise themselves. This allows scientists to design materials that do more than passively respond – they actively perform.

When buckling becomes continuous motion

In inactive materials, a simple structure under pressure may buckle and snap only once. For example, a paper ticket, an inactive form of matter, will bend or buckle when force is applied, but this response occurs just a single time.

This process of buckling and snapping drastically change when materials become active. To construct an active material that can undergo buckling and snapping, scientists connected a sequence of rods to form a chain, with small motors attached to the end points wherever two of these rods meet. The job of the motors was to make the interactions within the chain non-reciprocal: when rod A moves, rod B responds differently (by rotating over a different angle, for example) than rod A responds when rod B moves.

“The surprising result was that the chains constructed in this way still showed buckling and snapping when external forces were applied, but not just a single buckle and snap: the process could repeat, and oscillations could occur,” shared joint first author Sami Al-Izzi from the University of New South Wales.

“In technical terms, what happened was that the so-called critical point where the system snapped now became a critical exceptional point. In layman’s terms, this meant that the chains now could start to crawl, walk and even dig,” added the second joint first author Yao Du from the University of Amsterdam.

The findings point toward materials with potential applications in soft robotics and may form the basis for smarter robot bodies that operate independently of centralised control.

Rethinking a fundamental physics rule

In the second study, scientists examined how active materials behave in larger, two-dimensional structures. Their results challenge Le Chatelier’s Principle, which roughly states that what happens on a small scale also happens on a large scale.

“In particular, when the building blocks of an active material become more active, the structure as a whole may actually become less active,” stated first author Jack Binysh from the research group of Corentin Coulais at the University of Amsterdam.

“This was demonstrated by connecting similar motors and rods, this time not in a chain but in a two-dimensional lattice-like structure. The experiment measured how the elasticity of this structure as a whole depended on the properties of the individual building blocks.”

The crucial factor that determines the large-scale behaviour turned out to be the percolation of the active microscopic components throughout the material. Compare this to the percolation of water through coffee: when we make coffee, the powder should not be too dense, or the water will not get all the way through. Similarly, when there is a high density of less active components in a material, elastic responses will not always get through, even if all other components are extremely active.

The breaking of Le Chatelier’s Principle can be fundamentally important to researchers working with active microstructures such as biophysical gels, epithelial monolayers, and neuromorphic networks.

“Taken together, both the studies show how active materials can adapt, reorganise, and generate motion using their own internal energy. The research will be of broad interest across physics, soft matter science, mechanical engineering, life sciences, and robotics,” concluded Anton Souslov, Associate Professor at the Cavendish Laboratory, University of Cambridge, who was part of both the studies.

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References:

Sami C. Al-Izzi, Yao Du, Jonas Veenstra, Richard G. Morris, Anton Souslov, Andreas Carlson, Corentin Coulais, and Jack Binysh. ‘Non-reciprocal buckling makes active filaments polyfunctional.’ PNAS (March 2026). DOI: /10.1073/pnas.2531723123

Jack Binysh, Guido Baardink, Jonas Veenstra, Corentin Coulais, and Anton Souslov. ‘More is less in unpercolated active solids.’ Physical Review X (April 2026). DOI: 10.1103/flhb-kjyd

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Adapted from the original article by University of Amsterdam.