Unlike rigid electronics, living systems are soft and flexible. MIT engineers developed a biocompatible, flexible gel whose light-controlled conductivity could advance human-machine interfaces and soft robotics.
Welcome to the emerging field of ionotronics, which transmits information using ions—charged molecules—much like electronics relies on electrons. While electronic systems are established, ionotronics is still emerging—except in living organisms, where cells communicate via ions like potassium and sodium.
By bridging electronic systems and biological tissues, ionotronics opens possibilities for applications like soft wearables and human–machine interfaces.
“We’ve identified a way to dynamically regulate local ion concentrations in a soft material,” said Thomas J. Wallin, an MIT materials science professor leading the research. “This could enable systems that adapt to environmental stimuli, such as light.”
In other words, the system can automatically adjust to changes in light, enabling complex signal processing in soft materials. The findings were published online on February 21 in Nature Communications.
An Expanding Field
While others have created ionotronic materials with high conductivity that enable fast ion transport, their conductivity typically isn’t tunable. “We’re using light to switch a soft material from an insulator to one that’s 400 times more conductive,” said Xu Liu, the study’s lead author and incoming assistant professor at King’s College London.
At the core of this advance are PIGs, materials that can increase conductivity up to 1,000-fold under light. The MIT team embedded PIGs into polyurethane rubber by dissolving the powder in a solvent and using a swelling process.
Significant Potential
In the current material, the conductivity change is irreversible, though Liu believes future versions could reversibly switch between insulating and conductive states.
She adds that this study used just one type of photo-ion generator, polymer, and solvent, but many alternatives exist—opening the door to even more advanced light-responsive soft materials.
Liu also highlights the possibility of designing materials that react to other stimuli, such as heat or magnetic fields, expanding the concept beyond light.
“Our work could help establish a new subfield we call soft photo-ionotronics,” she says, noting its potential to drive innovations in soft machines, wearable technologies, human–machine interfaces, robotics, and biomedicine.
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