# Design of an injectable, self-adhesive, and highly stable hydrogel electrode for sleep recording

## TL;DR

A new injectable hydrogel electrode improves long-term EEG monitoring for sleep by offering better stability and signal quality.

## Contribution

The injectable hydrogel electrode AIRTrode enables long-term, high-quality EEG monitoring with superior adhesion and signal stability.

## Key findings

- AIRTrode achieves a low impedance of 17.53 kΩ for over 8 hours on hairy scalp regions.
- The hydrogel electrode has a high adhesion strength of 0.92 N cm−1 and maintains performance during daily activities and sleep.
- AIRTrode provides a signal-to-noise ratio of 23.97 dB, outperforming commercial wet electrodes.

## Abstract

High-quality and continuous electroencephalogram (EEG) monitoring is desirable for sleep research, sleep monitoring, and the evaluation and treatment of sleep disorders. Existing continuous EEG monitoring technologies suffer from fragile connections, long-term stability, and complex preparation for electrodes under real-life conditions. Here, we report an injectable and spontaneously cross-linked hydrogel electrode for long-term EEG applications. Specifically, our electrodes have a long-term low impedance on hairy scalp regions of 17.53 kΩ for more than 8 h of recording, high adhesiveness on the skin of 0.92 N cm−1 with repeated attachment capability, and long-term wearability during daily activities and overnight sleep. In addition, our electrodes demonstrate a superior signal-to-noise-ratio of 23.97 decibels (dB) in comparison with commercial wet electrodes of 17.98 dB and share a high agreement of sleep stage classification with commercial wet electrodes during multichannel recording. These results exhibit the potential of our on-site-formed electrodes for high-quality, prolonged EEG monitoring in various scenarios.

AIRTrode features preparation-free, tunable mechanical and electrical properties and superior adhesiveness to achieve a variety of biopotential recording applications. AIRTrode demonstrates a higher signal-to-noise ratio (SNR) than commercial EEG gel together with excellent long-term on-skin stability. The capability of AIRTrode to capture brain activity with higher signal quality and a significantly longer time span than commercial EEG gel holds significant potential for personalized healthcare applications. Our AIRTrode technology has the potential to minimize costs and enhance long-term health outcomes through tailored monitoring and interventions.