A novel flexible hydrogel electrode with a strong moisturizing ability for long-term EEG recording

Objective: A novel flexible hydrogel electrode with a strong moisturizing ability was prepared for long-term electroencephalography (EEG) monitoring. Approach: The hydrogel was synthesized by polymerizing the N-acryloyl glycinamide (NAGA) monomer. And a proper amount of glycerin was added to the hydrogel to increase the moisture retention ability of the electrodes. The hydrogel shows high mechanical properties, and the liquid in the hydrogel produces a hydrating effect on the skin stratum corneum, which could decrease the contact impedance between skin and electrode. In addition, the installation of hydrogel electrode is very convenient, and the skin of the subject does not need to be abraded. Main results: SEM images show that there are a large number of micropores in the hydrogel, which provide storage space for water molecules. The average potential drift of the hydrogel electrode is relatively low (1.974 ± 0.560 µV min-1). The average contact impedance of hydrogel electrode in forehead region and hair region are 6.43 ± 0.84 kΩ·cm2 and 13.15 ± 3.72 kΩ·cm2, respectively. The result of open/closed paradigm, steady-state visual evoked potentials (SSVEP), and P300 visual evoked potential show that hydrogel electrode has excellent performance. Compared with the hydrogel without glycerol, the moisture retention ability of hydrogel with glycerol was greatly improved. Significance. Compared with standard Ag/AgCl wet electrode, hydrogel electrode is more convenient to install and has strong moisture retention ability, which makes it have great potential in daily life for long-term EEG recording.