The future of brain activity monitoring may look like a strand of hair

UNIVERSITY PARK, Pa. — The future of electroencephalography (EEG) monitoring may soon look like a strand of hair. In place of the traditional metal electrodes, a web of wires and sticky adhesives, a team of researchers from Penn State created a hairlike device for long-term, non-invasive monitoring of the brain’s electrical activity. The lightweight and flexible electrode attaches directly to the scalp and delivers stable, high-quality recordings of the brain’s signals.

EEG is critical for diagnosing and assessing neurological conditions like epilepsy and brain injuries. In some cases, clinicians need to monitor brain waves for longer periods of time, for example, to evaluate seizures, sleep disorders and conditions that affect the blood vessels and blood flow in the brain.

The researchers described the new electrodes, which were shown to maintain stable performance for over 24 hours of continuous wear, in a study published in the journal npc biomedical innovations. This technology holds promise for use in consumer health and wellness products, in addition to clinical health care application, according to the researchers.

“This electrode allows for more consistent and reliable monitoring of EEG signals and can be worn without being noticeable, which enhances both functionality and patient comfort,” said Tao Zhou, Wormley Family Early Career Professor of engineering science and mechanics and senior author on the paper.

EEG monitoring is a widely used method to measure the brain’s electrical activity, Zhou explained. Small metal electrodes are placed on the scalp and pick up the faint electrical impulses generated by cells in the brain. The electrodes are attached to wires that are then connected to a machine that displays the brain’s activity as patterns that look like waves.

The traditional EEG monitoring process, however, can be a cumbersome — and sometimes messy — affair. Its limitations make it difficult to use for continuous, long-term monitoring.

To get a good recording of the brain’s activity, the electrodes need to conform to the scalp. Any gaps between the electrode and the skin or dense hair can diminish the quality of the recorded signal. Researchers and clinicians must apply gels to the scalp to maintain good surface-to-surface contact between the electrodes and skin and signal quality. For some people, though, the gels can cause skin irritation.

It’s a time-consuming process that must be repeated when the gels dry out, especially for someone needs to be monitored continuously or over the course of multiple sessions. The application and re-application process is imprecise, too, and can result in different amounts of gel used on the electrodes.

“This will change the impedance — or interface — between the electrodes and the scalp and it can affect the brain signal that’s recorded,” Zhou said. “We also don’t always apply the electrodes in the exact same position either because we’re human. But if you change the position, even a little bit, the brain signals you’re monitoring can be different.”

The conventional EEG electrodes are rigid, too, and can shift when someone moves their head, even slightly, which can compromise the data uniformity.

To address these limitations, the research team designed a small monitoring device that looks like a strand of hair and is made from 3D-printed hydrogel material. One end is the electrode. It looks like a small dot and captures the brain’s electrical signals from the scalp. There’s a long, thin wire-like component that extends from the electrode, which connects to the monitoring system.

The device also uses a 3D-printable bioadhesive ink that allows the electrode to stick directly onto the scalp without the need for any gloopy gels or other skin preparation. This minimizes the gap between the electrode and scalp, improving the signal quality. The lightweight, flexible and stretchable nature of the device also means that the device stays put — even when combing hair and donning and removing a baseball cap — and can be worn for longer periods of time, making it suitable for chronic monitoring.

The team found that the new device performed comparably to gold electrodes, the current standard electrodes used for EEG. However, the hairlike electrode maintained better contact between the electrode and skin and performed reliably for over 24 hours of continuous wear without any degradation in signal quality. Because the electrodes don’t have to be removed and replaced like traditional EEG monitoring systems, they eliminate the risk of inconsistent data, even across different monitoring sessions.

“You don’t have to worry if the position of the electrode has changed or if the impedance has changed because the electrodes haven’t moved,” Zhou said.

Unlike the traditional metal electrodes, the new electrodes mimic human hair and are inconspicuous on the head. Since the device is 3D-printed, Zhou explained that they can print the electrode in different colors to match a person’s hair, too.

“This makes it discreet, and people may be more comfortable wearing this, especially if they require continuous EEG monitoring and need to wear the electrodes for an extended period of time,” Zhou said.

Currently, the EEG is still wired; patients need to be connected to a machine while their brain activity is recorded. In the future, the researchers hope to make the system wireless so that people can move around more freely during recording sessions.

Other Penn State authors on the paper include lead authors Salahuddin Ahmed and Marzia Momin, both doctoral students in the Department of Engineering Science and Mechanics. Jiashu Ren, doctoral student in the Department of Engineering Science and Mechanics; Hyunjin Lee, doctoral student in the Department of Biomedical Engineering; Li-Pang Huang, research assistant; and Basma AlMahmood, undergraduate student in the Department of Physics also contributed to the paper.

Other authors include Chi-Ching Kuo, Archana Pandiyan and Loganathan Veeramuthu from the Department of Molecular Science and Engineering, National Taipei University of Technology.

Funding from the National Institutes of Health; Oak Ridge Associated Universities; the National Taipei University of Technology-Penn State Collaborative Seed Grant Program; and the Department of Engineering Science and Mechanics, the Materials Research Institute and the Huck Institutes of Life Sciences at Penn State supported this work.