In a study published on August 22, Cell Report Physical SciencesA research team led by Dr. Yoshikatsu Hayashi demonstrated that a simple hydrogel – a type of soft, flexible material – could learn how to play the simple 1970s computer game Pong. Interfaced with a computer simulation of this classic game via a custom-built multi-electrode array, the hydrogel improved in performance over time.
Dr Lin, a biomedical engineer from the University of Reading's School of Biological Sciences, said: “Our work shows that even very simple materials can exhibit complex, adaptive behaviours typically associated with biological systems and advanced AI.”
“This opens up exciting possibilities for developing new types of 'smart' materials that can learn and adapt to their environment.”
The emergent learning behavior is thought to arise from the movement of charged particles within the hydrogel in response to electrical stimuli, creating a kind of “memory” within the material itself.
“Ionic hydrogels can achieve memory mechanisms similar to those found in more complex neural networks,” said first author Vincent Strong, a robotics engineer at the University of Reading. “We've demonstrated that not only can the hydrogels play Pong, but they can actually get better at it over time.”
The researchers were inspired by previous work that showed that people could learn to play Pong by electrically stimulating brain cells in a dish and giving them feedback on their performance.
“Our paper addresses the question of whether a simple artificial system can compute closed loops similar to the feedback loops that allow our brains to control our bodies,” said Dr. Hayashi, corresponding author of the study.
“The fundamental principle of both neurons and hydrogels is that the movement and distribution of ions serves as a memory function that correlates with the sensory-motor loop of the Pong world. In neurons, ions flow inside the cell, while in gels they flow outside.”
As most existing AI algorithms are derived from neural networks, the researchers say that hydrogels represent a different kind of “intelligence” that could be harnessed to develop new, simpler algorithms. In the future, the researchers plan to further explore the hydrogel's “memory” by examining the mechanisms behind its memory and testing its ability to perform other tasks.
Beating gel mimics heart tissue
In a recently published related study, Proceedings of the National Academy of SciencesDr Lin's team, along with colleagues Dr Zuowei Wang and Dr Nandini Vasudevan from the University of Reading, have demonstrated how different hydrogel materials can be made to beat to the rhythm of an external pacemaker – the first time this has been achieved using materials other than living cells.
The researchers demonstrated how hydrogel materials can vibrate chemically and mechanically in a manner similar to the way heart muscle cells contract in unison, and they provide a theoretical interpretation of these dynamic behaviors.
The researchers found that by subjecting the gel to cyclic compression, they could entrain the gel's chemical oscillations to a mechanical rhythm, and the gel retained a memory of this synchronized beat even after the mechanical pacemaker was turned off.
“This is an important step towards developing a myocardial model that may be used in the future to study the interplay between mechanical and chemical signals in the human heart,” said Dr. Lin. “It opens up the exciting possibility of replacing some animal experiments in cardiac research with chemically driven gel models.”
Dr Tunde Geher Herceg, lead author of the study, said the discovery could provide a new way of investigating arrhythmias, which affect more than two million people in the UK and cause the heart to beat too fast, too slow or irregularly.
“Arrhythmias can be managed with drugs or electronic pacemakers, but the complexity of biological heart cells makes it difficult to study the underlying mechanical systems independently of the heart's chemical and electrical systems,” she said.
“Our findings may lead to new discoveries and potential treatments for arrhythmias and will contribute to our understanding of how artificial materials can be used instead of animals or biological tissues in future research and treatments.”
Implications and future directions
These studies bridge concepts from neuroscience, physics, materials science and cardiac research and suggest that the fundamental principles underlying learning and adaptation in biological systems may be more universal than previously thought.
The researchers believe their discovery could have far-reaching implications for fields ranging from soft robotics and prosthetics to environmental sensing and adaptive materials.
Future research will focus on developing more complex behaviors and exploring potential real-world applications, such as advancing cardiac research and developing alternative experimental models to reduce the use of animals in medical research.
More information:
Electroactive polymer hydrogels exhibit emergent memory when incorporated into a simulated gaming environment. Cell Report Physical Sciences (2024). DOI: 10.1016/j.xcrp.2024.102151. www.cell.com/cell-reports-phys … 2666-3864(24)00436-3
Tunde Geher-Herczegh et al. “Harmonic resonance and tuning of chemical wave propagation by external mechanical stimulation in BZ self-oscillating hydrogels” Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2320331121
Provided by University of Reading
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