A small blob of squishy, transparent gel has recently demonstrated an impressive feat: it can play the classic video game Pong, and with practice, it even gets better at it. When connected to an adapted version of the game via an electrode array, this simple polymer hydrogel showed a marked improvement in accuracy, leading to longer rallies. This discovery reveals that even a basic material like hydrogel can exhibit a form of memory—a finding that could open new avenues for research and development.

Although the gel is far from being an artificial brain, its newfound ability hints at exciting possibilities. “Our research shows that even very simple materials can exhibit complex, adaptive behaviors typically associated with living systems or sophisticated AI,” said biomedical engineer Yoshikatsu Hayashi of the University of Reading in the UK. “This opens up exciting possibilities for developing new types of ‘smart’ materials that can learn and adapt to their environment.”

The hydrogel in question is based on an electro-active polymer (EAP), a type of polymer that changes its size or shape when an electric current is applied. EAPs are commonly used in actuators and sensors as a form of artificial muscle. In 2022, a team of researchers showed that a glob of human brain cells in a dish could be taught to play Pong by providing feedback on whether it successfully hit a pixel “ball” with a pixel “paddle.”

Building on this idea, biomedical engineers Vincent Strong, William Holderbaum, and Hayashi, all from the University of Reading, sought to determine whether a similar learning ability could be demonstrated in something much simpler than human brain tissue. The logical test subject was EAP hydrogel. When an electric current is applied, ions—charged particles—within the hydrogel’s matrix of crosslinked polymer chains move, causing the gel to change shape. Previously, Hayashi and his team showed how this phenomenon could be used to make hydrogel beat in sync with a pacemaker, mimicking the beating of a heart.

During that research, they noticed that their polyacrylamide hydrogel retained a “memory” of the beating, even after the pacemaker was turned off. “The rate at which the hydrogel de-swells takes much longer than the time it takes for it to swell in the first place, meaning that the ions’ next motion is influenced by its previous motion, which is sort of like memory occurring,” Strong explained.

The team used electrical stimulation to inform the gel of the randomized position of the ball in Pong and measured the flow of ions to determine the paddle’s position. They also observed how long each rally—back-and-forth exchanges between the gel-controlled paddle and the wall—lasted and found that the rallies grew longer over time. It took the gel around 20 minutes to reach its peak Pong skill level.

“Over time, as the ball moves, the gel gathers a memory of all motion. And then the paddle moves to accommodate that ball within the simulated environment,” Strong noted. “The ions move in a way that maps a memory of all motion over time, and this ‘memory’ results in improved performance.”

The researchers say this memory is an emergent ability, not something the material was specifically designed or trained for. However, this doesn’t mean the material is sentient or acting deliberately—it simply retains an impression of a physical influence, much like the way skin retains the imprint of a crinkly pillow.

Despite its simplicity, this finding opens intriguing possibilities for future research. One of the next steps is to determine the mechanisms behind the memory and explore whether the material can be trained to perform other tasks. “We’ve shown that memory is emergent within the hydrogels, but the next step is to see whether we can also show specifically that learning is occurring,” Strong concluded.

By Impact Lab