High-Conductivity, Low-Impedance, and High-Biological-Adaptability Ionic Conductive Hydrogels for Ear-EEG Acquisition

High conductivity, low impedance, and high biological adaptability are essential characteristics of the materials used to acquire bioelectrical information. Here, we report on a wearable sensor with stable and accurate signal detection for bioelectrical data acquisition based on an ion-conducting hydrogel with high conductivity. The proposed ion-conducting hydrogel is obtained by adding hydroxypropyl methyl cellulose (HPMC) into the poly(vinyl alcohol) (PVA) matrix to form a physical cross-linking. The prepared hydrogel has extremely high electrical conductivity after being soaked in a NaCl solution with a concentration of 5 M. The conductivity is up to 7.26 S/m, and the impedance is less than 8 Ω. The bioelectrode made of an ion-conducting hydrogel can be worn for up to 8 h without obvious skin irritation. The assembled ear-electroencephalogram (ear-EEG) acquisition system, which is based on ionic conducting hydrogels, can be worn as easily as sports headphones and can accurately collect EEG signals under various motion states. The system has potential applications in biological signal acquisition.