Physicists have developed a new method for coating soft robots with materials that enable them to move and operate more purposefully. The study, performed by the University of Bath in the United Kingdom, was published today in Science Advances.
The study’s authors think their breakthrough modeling on ‘active matter’ might signal a watershed moment in robot creation. With further refinement of the idea, it may be feasible to decide the form, mobility, and behavior of a soft solid based on human-controlled activity on its surface rather than its inherent elasticity.
An average soft material’s surface always shrinks into a spherical. Consider how water beads into droplets: the beading happens because the surface of liquids and other soft materials naturally compresses into the lowest surface area possible – a spherical. However, active matter may be tailored to counteract this propensity. A rubber ball encased in a layer of nano-robots, where the robots are programmed to operate in unison to deform the ball into a new, pre-determined shape, is an example of this in action (say, a star).
It is envisaged that active matter will give rise to a new generation of devices whose functions will be determined from the ground up. Instead of being guided by a single controller (like today’s factory-controlled robotic arms are), these new machines would be composed of several independent active components that collaborate to decide the machine’s movement and function. This is similar to how our own biological tissues operate, such as the fibers in heart muscle.
Scientists might use this concept to create soft machines with arms made of flexible materials that are driven by robots implanted in their surface. By covering the surface of nanoparticles with a responsive, active substance, they might also modify the size and form of drug delivery capsules. This, in turn, may have a significant impact on how a medicine interacts with cells in the body.
Work on active matter calls into question the idea that the energetic cost of a liquid or soft solid’s surface must always be positive since a certain amount of energy is always required to generate a surface.
The study’s original author, Dr. Jack Binysh, stated: “Active matter forces us to reconsider long-held natural laws, such as the need that surface tension be positive. It’s an interesting place to be conducting research to see what happens when we violate these norms and how we can use the data.”
Dr. Anton Souslov, the corresponding author, added: “This work is an essential proof of concept with several practical applications. Future technology, for example, might create soft robots that are considerably squishier and better at picking up and handling delicate items.”
The researchers used theories and simulations to characterize a 3D soft solid with active stresses on its surface for the study. They discovered that active strains stretch the material’s surface, pushing the solid underneath it along with it and generating a global shape shift. The researchers discovered that by adjusting the elastic characteristics of the material, the exact form of the solid could be adjusted.
The researchers will use this fundamental idea to develop specialized robots, such as soft limbs or self-swimming materials, in the next phase of this effort, which has already started. They will also investigate collective behavior, such as what occurs when a large number of active solids are crowded together.
The Universities of Bath and Birmingham collaborated on this project. The Engineering and Physical Sciences Research Council (EPSRC) financed it with New Investigator Award no. EP/T000961/1.