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Fast, Flexible Ionic Transistors for Bioelectronic Devices
February 28, 2019 | Columbia EngineeringEstimated reading time: 4 minutes
“Importantly, we only used completely biocompatible material to create this device. Our secret ingredient is D-sorbitol, or sugar,” says Khodagholy. “Sugar molecules attract water molecules and not only help the transistor channel to stay hydrated, but also help the ions travel more easily and quickly within the channel.”
Because the IGT could significantly improve the ease and tolerability of electroencephalography (EEG) procedures for patients, the researchers selected this platform to demonstrate their device’s translational capacity. Using their transistor to record human brain waves from the surface of the scalp, they showed that the IGT local amplification directly at the device-scalp interface enabled the contact size to be decreased by five orders of magnitude—the entire device easily fits between hair follicles, substantially simplifying placement. The device could also be easily manipulated by hand, improving mechanical and electrical stability. Moreover, because the micro-EEG IGT device conforms to the scalp, no chemical adhesives were needed, so the patient had no skin irritation from adhesives and was more comfortable overall.
These devices could also be used to make implantable closed loop devices, such as those currently used to treat some forms of medically refractory epilepsy. The devices could be smaller and easier to implant, and also provide more information.
“Our original inspiration was to make a conformable transistor for neural implants,” Gelinas notes. “While we specifically tested it for the brain, IGTs can also be used to record heart, muscle, and eye movement.”
Khodagholy and Gelinas are now exploring if there are physical limits to what kind of mobile ions they can embed into the polymer. They are also studying new materials into which they can embed mobile ions as well as refining their work on using the transistors to make integrated circuits for responsive stimulation devices.
“We are very excited that we could substantially improve ionic transistors by adding simple ingredients,” Khodagholy
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