Behind this ability lies a complex network of neurons and the synchronized movement of ions within our muscles.

For decades, scientists have striven to replicate this intricate mechanism in artificial devices, particularly in robots.

Today, robots have become indispensable across industries, from assembling cars to packaging food. Among these robots are “soft” ones that feature a pliable, rubber-like exterior designed to grasp items — such as hot dog or soap — from a conveyor belt and accurately package them. However, compared to human hands, these robotic appendages, typically operated by hydraulics or pneumatics, are limited in their versatility and as such programmed for a single task.

The aspiration has always been to construct robots analogous to biological organisms.

A promising material candidate for that is hydrogels (or simply, gels) — ubiquitous in products like food jelly and shaving gel — similar in composition to living beings: a network of crosslinked long molecules known as polymers that can draw and store vast amounts of water.

However, man-made gels at visible sizes are known to deform very slow whereas animal tissues, which are simply biological gels, can deform very fast in response to internal or external cues.

Our research team at Virginia Tech, together with our collaborators at the Radboud University in the Netherlands, have made significant strides to close this performance gap.

Previously, our team had done experiments by using a thin gel layer comprised of polyacrylic acid, a commonly used polymer, that can store copper or calcium ions.

We had observed that, upon exciting the gel with acid, the gel rapidly releases the ions while temporarily swelling due to osmosis, that is, water inflow.

Osmosis typically occurs as the movement of water through a selective membrane, which permits water but prevents bigger molecules like polymers from moving through.

For example, living organisms use osmosis to burst seed dispersing fruits in plants or absorbing water in the intestine. In our case, even though the gel surface is not in any way selective, osmosis was still observed and with an unusually elevated rate.

To explain this puzzling observation, we developed a new mathematical and experimental understanding. This has revealed that microscopic interactions between ions and polymers can attract water from outside as a new way of osmosis without a need of a selective interface.

What is more, this newly discovered microscopic mechanism allows gels to swell much faster by sucking water than has previously been possible.

Our findings have promising implications: Imagine manufacturing processes streamlined by agile robots capable of delicate, precise movements, or soft robots probing various terrains and obstacles by swiftly adapting to them.

Furthermore, design of minute gel-based shape-shifting capsules for smart drug delivery could revolutionize personalized health care applications, while innovations in contact lenses could offer enhanced comfort and vision correction.

As research progresses, the potential for scaling up this technology becomes increasingly apparent.

The vision of integrating robots seamlessly into everyday life, mirroring the adaptability and efficiency of, for instance, human hands or octopus arms, edges closer to reality.

With ongoing advancements in hydrogel technology, the future holds promise for a new era where robots not only assist but actively collaborate in diverse aspects of human endeavor, transforming industries and enriching lives worldwide.