Jelly plays Pong and gets better at with practice

A hydrogel has learned to play the 1970s video game “Pong” and improved its ability to hit the ball by 10% with some practice.

Dr Hayashi, a biomedical engineer at the University of Reading in the UK, says: “Our research shows that even very simple materials can exhibit complex, adaptive behaviours typically associated with living systems or sophisticated AI.  

“This opens up exciting possibilities for developing new types of ‘smart’ materials that can learn and adapt to their environment.” 

The research is described in a paper published in Cell Reports Physical Science.

An example run of a hydrogel playing Pong. Credit: Cell Reports Physical Science/Strong et al.

What is a hydrogel?

A hydrogel, like gelatine or agar, is made of a 3D network of polymers that become jelly-like when water is added.

The hydrogel in this study is an “ionic electro-active polymer”, where the media surrounding the polymer matrix contains charged particles, in this case hydrogen ions.

As a result, it can deform when an electric current is applied to it.

Stimulation by an electric field causes the hydrogen ions migrate and, as they move, drag water molecules with them, causing areas to swell.

“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,” says first author and University of Reading robotics engineer, Dr Vincent Strong.

“The continued rearrangement of ions within the hydrogel is based on previous rearrangements within the hydrogel, continuing back to when it was first made and had a homogeneous distribution of ions.”

It’s this property the researchers exploited to teach the hydrogel to play Pong.

How does a hydrogel play Pong?

Pong is a simple 2-dimensional game that simulates table tennis. Players control their paddle by moving it vertically across the left or right side of the screen to hit the ball.

Hooking up a hydrogel to an electrode array to play Pong. Credit: Cell Reports Physical Science/Strong et al.

In this case, the researchers hooked the hydrogel up to a virtual game environment using an array of electrodes. It controlled a paddle on the left side of the game environment and the ball rebounded off a stationary wall to the right.

They used electrical stimulation to inform the hydrogel of the ball’s position and measured the movement of ions within the hydrogel to determine the position of its paddle.

“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,” says Strong.

“The ions move in a way that maps a memory of all motion over time, and this ‘memory’ results in improved performance.”

The hydrogel was able to hit the ball more frequently with more experience, resulting in longer rallies (the number of times the ball was hit before it was missed). 

The researchers plan to further explore the hydrogel’s “memory” by examining the mechanisms behind it and testing its ability to perform other tasks.