Hydrogels can play Pong by 'remembering' previous patterns of electrical simulation
Non-living hydrogels can play the video game Pong and improve their gameplay with more experience, researchers report.
"Ionic hydrogels can achieve the same kind of memory mechanics as more complex neural networks," says first author and robotics engineer Vincent Strong of the University of Reading. "We showed that hydrogels are not only able to play Pong; they can actually get better at it over time."
The researchers were inspired by a previous study that showed that brain cells in a dish can learn to play Pong if they are electrically stimulated in a way that gives them feedback on their performance.
"Our paper addresses the question of whether simple artificial systems can compute closed loops similar to the feedback loops that allow our brains to control our bodies," says corresponding author and biomedical engineer Yoshikatsu Hayashi of the University of Reading. "The basic principle in both neurons and hydrogels is that ion migration and distributions can work as a memory function that can correlate with sensory-motor loops in the Pong world. In neurons, ions run within the cells; in the gel, they run outside."
Hydrogels are complex polymers that become jelly like when hydrated -- gelatin and agar are natural examples. In this case, the researchers used an "electro-active polymer," meaning a hydrogel that can respond to electrical stimulation thanks to the presence of ions (charged particles) in the media surrounding its polymer matrix. When the hydrogel is electrically stimulated, the ions move, dragging water molecules with them, and this movement causes the hydrogel to temporarily change shape.