Mechanically robust, highly conductive, and adhesive zwitterionic enhanced gelatin organic hydrogel with thermally reversible phase transition suitable for EEG electrodes

Electroencephalography (EEG) devices have witnessed significant advancements in the field of medicine and brain-computer interface. However, wet electrodes widely used in hospitals and clinics require filling with conductive paste, and the installation and removal processes are complex, posing challenges in daily EEG monitoring. Herein, we prepared a novel organic conductive hydrogel with a dual physically cross-linked network by facilely combining the thermally reversible phase transition of gelatin with an amphiphilic zwitterionic [2-(methacryloxy) ethyl] dimethyl-(3-propyl sulfonic acid) ammonium hydroxide in a glycerol-water binary solvent system. The hydrogel exhibits outstanding tensile strength (0.66 MPa) and elongation (525.7 %), very low skin-electrode contact impedance (3.54 kΩ at 10 Hz), and remarkable moisture retention (72 h). It demonstrates good adhesion to various substrates and can transform from a liquid sol at high temperatures to a solid gel at low temperatures (phase transition temperature of 43.6 ℃). Therefore, this hydrogel can penetrate the hair in the gel dissolving state, and firmly adhere to the scalp after solidification, forming a tight electrode-skin contact interface. This provides an effective strategy for long-term daily use in EEG monitoring.