Integrating first-of-its-kind washable hydrogel electrodes with a pulse sensor, researchers from the University of Massachusetts Amherst have developed smart eyewear to track eye movement and cardiac data for physiological and psychological studies. The eyewear--known as Chesma and presented August 20 in the journal Matter--provides accurate measurements in an everyday environment without compromising users' comfort.
"Our mask can track people's eye movement as they're shown images, so you can start to understand what they're paying attention to, for how long, whether they keep finding other places to look," says senior author Trisha L. Andrew of the University of Massachusetts Amherst.
Current technology for eye movement tracking relies on electrooculography (EOG), a technique designed over 50 years ago to measure the eye's electrical potential changes. "The problem is that you have to stick those adhesive electrodes on your face," says Andrew. "But people tend to be a little finicky about stuff put on their face, unsurprisingly."
One challenge in designing smart wearables is developing products that provide both accuracy and comfort. To achieve that, Andrew and her colleagues developed a novel hydrogel electrode by growing polymers on fabrics. Reaching the nooks and cranny of the fiber pattern, the hydrogel polymer bonds to and covers the fabric's topology, resulting in a mechanically stable coating that is imperceptible to one's eye and touch.
The team then combined these hydrogel electrodes with a pulse sensor to create an eye mask that can track eye movements and collect cardiac signals from the artery located at the brow bone. "Our team was able to really address that core problem to create a garment that you would be willing to wear and give you clinically accurate results when you use it," says Andrew. The research team, composed of Iranian, Indian American, Armenian-Greek, and Chinese American scientists named the eyewear Chesma, a word meaning eyeglasses or eyes in many of their languages.
One clinical use of the mask might be to monitor sleep. "One of the biggest classifiers between sleep stages is how radically you move your eyes," says Andrew. "We could correlate some of these sleep stages and also start to understand whether you have sleep disorder problems or if you have some underlying heart rate issues."
Besides performing as well as the adhesive clinical electrodes currently in use, the hydrogel electrodes used in Chesma are also extremely durable. The hydrogel can resist long-term build-up from makeup, pollution, and skin waste that may fault the electrodes, as well as withstand 15 laundry cycles. And the researchers found that Chesma's signal did not display any degradation after 6 hours of continuous use without rehydrating the hydrogel, suggesting that it could be worn for long periods of time. In fact, the hydrogel retains water so well that it takes almost 40 hours to dry out completely--and even if it does, Andrew says simply "a couple of drops of water on it, let it sit for about 30 seconds, and it becomes like gelatin once more."
Next, the research team wants to reduce the power demand of the device, which would allow users to charge the device once every three nights instead of every 8 hours. The extended battery life can also facilitate potential applications during people's waking hours. Besides its potential uses in health monitoring, the team would also like to see it deployed in other fields such as virtual reality and gaming or advertisement performance analysis, where it could help researchers understand if an ad literally "caught people's eye."
This work was supported by the National Science Foundation and the David and Lucile Packard Foundation.
Matter, Homayounfar et al.: "Multimodal Smart Eyewear for Longitudinal Eye Movement Tracking" https://www.cell.com/matter/fulltext/S2590-2385(20)30388-X
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