Recent Advances in Gel-Free Scalp EEG Electrodes: Materials, Structures, and Fixation Strategies

In this review, the development of gel-free scalp electroencephalography (EEG) electrodes is summarized from three aspects: material selection, structural design, and head fixation strategies. The focus is on analyzing the role of these factors in balancing the impedance at the electrode–scalp interface with wearing comfort. Electrode materials have evolved from rigid metals to flexible polymers, textiles, and hydrogels, thus mitigating mechanical modulus mismatch with the scalp. Structural design includes optimizing the comb-like configurations of the electrode contact interfaces—such as claw, brush, and arch shapes—coupled with integrated external cushioning structures, such as springs or foams, to increase the contact stability and suppress motion artifacts. Fixation methods have evolved from rigid caps to flexible elastic caps with self-adhesive interfaces, thereby achieving conformable contact, simplified installation, and improved comfort. Collectively, these technological advances provide effective strategies for increasing electrode-scalp coupling stability and signal quality in gel-free EEG systems.