Abstract
Noninvasive brain-computer interface (BCI) has been extensively studied from many aspects in the past decade. In order to broaden the practical applications of BCI technique, it is essential to develop electrodes for electroencephalogram (EEG) collection with advanced characteristics such as high conductivity, long-term effectiveness, and biocompatibility. In this study, we developed a silver-nanowire/PVA hydrogel/melamine sponge (AgPHMS) semidry EEG electrode for long-lasting monitoring of EEG signal. Benefiting from the water storage capacity of PVA hydrogel, the electrolyte solution can be continuously released to the scalp-electrode interface during used. The electrolyte solution can infiltrate the stratum corneum and reduce the scalp-electrode impedance to 10 kΩ-15 kΩ. The flexible structure enables the electrode with mechanical stability, increases the wearing comfort, and reduces the scalp-electrode gap to reduce contact impedance. As a result, a long-term BCI application based on measurements of motion-onset visual evoked potentials (mVEPs) shows that the 3-hour BCI accuracy of the new electrode (77% to 100%) is approximately the same as that of conventional electrodes supported by a conductive gel during the first hour. Furthermore, the BCI system based on the new electrode can retain low contact impedance for 10 hours on scalp, which greatly improved the ability of BCI technique.
Highlights
A comfortable gel-free electrode with a facile preparation process, high conductivity, good mechanical and electrochemical stability, longterm service, and sustained release ability of electrolyte is highly desired for a noninvasive brain-computer interface (BCI) system
Before the cross-link process, sodium chloride and glycerol solution were added to the hydrogel precursor to more effectively reduce the resistance of the stratum corneum by the electrolyte released in the hydrogel
X-ray powder diffraction (XRD) (Figure S1), X-ray photoelectron spectroscopy (XPS) (Figure S2), Thermogravimetric analysis (TGA), and differential thermal analysis (Figure S3) of the metalized sponge suggest that the sponge was metalized and thermally stable
Summary
There are increasingly demands for communication between humans and computers [1–3]. The brain-computer interface (BCI) is a technique of communication based on neural activity generated by the brain and is independent of the brain’s normal output pathway of peripheral nerves and muscles; the BCI is a novel communication channel without the use of traditional human-computer interaction equipment, such as a keyboard and mouse [4–8]. In many BCI applications or studies, commercial dry electrodes and wet electrodes have been widely used to collect EEG signals [30, 31]. Since the stratum corneum of the scalp is infiltrated by the electrolyte in the conductive gel, the contact impedance between the scalp and electrode is significantly reduced when the wet electrode is used [39]. To ensure the stability of the structure, the semidry electrode with a microporous and water tank structure is rigid This leads to discomfort that is similar to that of wearing commercially dry electrodes, and the small scalp-electrode contact surface causes relatively high contact impedance. A comfortable gel-free electrode with a facile preparation process, high conductivity, good mechanical and electrochemical stability, longterm service, and sustained release ability of electrolyte is highly desired for a noninvasive BCI system. The new electrode shows high conductivity, good flexibility, and remarkable electrochemical and mechanical stabilities, which are highly expected for the widely application of long-term noninvasive BCI systems
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