Active matter: the future of robotics

With additional development of the concept, it could be possible to ascertain the shape, movement, and behaviour of a soft solid by human-controlled activity on its surface. This research was funded by the Engineering and Physical Sciences Research Council through a New Investigator Award.

The work has been published in the journal Science Advances.

Active matter

Active matter includes both living and non-living systems containing energy-consuming and force-generating microscopic constituents that drive emergent dynamic properties on larger scales.

Active matter can be designed to work against the usual tendency of the surface of soft material, which usually shrinks into a sphere. Imagining the way water beads into droplets can help this make better sense. The beading happens because the surface of liquids and other soft material naturally contracts into the smallest surface area possible, a sphere.

Thinking of this in action, imagine a rubber ball wrapped in a layer of pre-programmed nano-robots. The nano-robots are programmed to work in unison to distort the ball into a different, pre-determined shape, for example a rectangle.

Active matter research challenges the assumption that the energetic cost of the surface of a liquid or soft solid must always be positive because a certain amount of energy is required to create a surface.

The study involved researchers developing theory and simulations that described a 3D solid experiencing active stresses on its surface. They unearthed that these active stresses expand the surface of the material, pulling the solid underneath with it, causing a global shape change. The precise shape adopted by the solid could be tailored by altering the elastic properties of the material.

Dr Jack Binysh, first author of the team’s work said: “Active matter makes us look at the familiar rules of nature, rules like the fact that surface tension has to be positive, in a new light. Seeing what happens if we break these rules, and how we can harness the results, is an exciting place to be doing research.”

Applications

The work has the potential to lead to soft machines with flexible arms driven by surface-embedded robotics, or drug delivery capsules with customised sizes and shapes. This could influence how a drug interacts with cells in the body.

Such machine’s function will come from the bottom up, meaning they would be comprised of individual active units that cooperate to determine the machine’s movement and function. This differs from the way current robotic arms are controlled in factories, governed by a central controller.

Dr Anton Souslov, corresponding author said: “This study is an important proof of concept and has many useful implications. For instance, future technology could produce soft robots that are far squishier and better at picking up and manipulating delicate materials.”

Next phase of work

The next phase of development has already begun. Researchers will apply the general principle of active matter to design specific robots, including soft arm or self-swimming materials. The team will also research collective behaviour, focusing on what happens when you have lots of active solids packed together.