New hydrogel electrodes sense eye motion comfortably

On Aug. 17 at the ACS Fall 2020 Virtual Meeting during a presentation in the Polymeric Materials: Science and Engineering Division, researchers reported on a reusable hydrogel electrode that can track eye motion with excellent signal quality without compromising on comfort. The new fabric-based device could be used for sleep studies and virtual reality equipment.

Common medical-grade electrodes use a combination of conductive gel and adhesives that make a tight bond with the skin, allowing for high quality measurements of electrical signals. But these electrodes can only be used once and they irritate the skin. That makes it hard for people to wear wet electrodes on the face or head for long periods of time, which is common in sleep studies. Electrodes made of dry, conducting metals have also been developed, but they don’t make consistent contact with skin, especially when the wearer is moving their face.

A team led by S. Zohreh Homayounfar and Trisha Andrew, materials chemists at the University of Massachusetts Amherst, set out to make a more comfortable fabric-based electrode that could provide the same fidelity of measurements as sticky, irritating medical electrodes. They built a device that people can wear on their face to track eye motion.

Homayounfar made a squishy electrode by coating a square of conductive textile made of cotton and silver thread with a layer of medical-grade silver gel. Then she used initiative chemical vapor deposition to form a network of poly(2-hydroxyethylacrylate) (pHEA) that crosslinked with the gel and grafted to the fabric backing. This resulted in a mechanically stable, ion-conducting hydrogel composite that is safe to use on human skin (Matter 2020, DOI: 10.1016/j.matt.2020.07.030).A few drops of water fully hydrate the electrode in minutes, but it takes 40 h for the material to dry out.

The team sewed the hydrogel electrodes into a mask to make an eye-movement tracker, adding a second fabric-based pressure sensor to measure the wearer’s pulse. The fabric-based components worked as well as sensors that use adhesive-based electrodes, without any of the discomfort. Whether the wearer was awake or asleep, chewing or nodding, wearing makeup or sweaty, the mask worked well for 8 hours of continuous use.

The team also tested the mask’s durability. The hydrogel electrodes must stay hydrated to function, but Homayounfar says they can be rehydrated more than 30 times. And the electrodes can be washed with laundry detergent 15 times without breaking down.

Jun Chen, a bioengineer at the University of California, Los Angeles, who was not involved in the study, was impressed by the resilience of the sensor in everyday settings. “This is certainly an outstanding work with a novel approach for wearable physiological monitoring,” he wrote in an email.

Homayounfar says the mask “will enable a host of cutting edge biomedical and psychological studies in addition to improving gaming and virtual reality headsets.”