Electroencephalography (EEG) captures minute electrical signals emanating from the brain. These signals are vulnerable to interference from external noise and dynamic artifacts; hence, accurately recording such signals is challenging. Although dry electrodes are convenient, their signals are of limited quality; consequently, wet electrodes are predominantly used in EEG. Therefore, developing dry electrodes for accurately and stably recording EEG signals is crucial. In this study, we developed flexible dry electrodes using polydimethylsiloxane (PDMS)/carbon-nanotube (CNT) composites with isotropically wrinkled surfaces that effectively combine the advantages of wet and dry electrodes. Adjusting the PDMS crosslinker ratio led to good adhesion, resulting in a highly adhesive CNT/PDMS composite with a low Young’s modulus that exhibited excellent electrical and mechanical properties owing to its ability to conformally contact skin. The isotropically wrinkled surface also effectively controls dynamic artifacts during EEG signal detection and ensures accurate signal analysis. The results of this study demonstrate that dry electrodes based on flexible CNT/PDMS composites and corrugated structures can outperform wet electrodes. The introduction of such electrodes is expected to enable the accurate analysis and monitoring of EEG signals in various scenarios, including clinical trials.

Polymers mixed with conductive fillers hold significant potential for use in stretchable and wearable sensor devices. Enhancing the piezoresistive effect and mechanical stability is critical for these devices. To explore the changes in the electrical resistance under high strains, typically unachievable in single-layer composites, bi-layer structures were fabricated from carbon nanotubes (CNTs) and EcoFlex composites to see unobservable strain regions. Spherical types of non-conductive fillers composed of polystyrene and conductive filler, coated with Ni and Au on non-conductive fillers, were used as secondary fillers to improve the piezoresistive sensitivity of composites, and their respective impact on the conductive network was compared. The electrical and mechanical properties were examined in the static state to understand the impact of these secondary fillers. The changes in the electrical resistance under 100% and 300% tensile strain, and their dependence on the inherent electrical properties of the secondary fillers, were also investigated. Single-layer CNT composites proved incapable of withstanding 300% strain, whereas the bi-layer structures proved resilient. By implementing cyclic stretching tests, contrary to non-conductive fillers, reduced piezoresistive influence of the conductive secondary filler under extreme strain conditions could be observed.

Gallium-based liquid metals remain in a liquid state at room temperature and exhibit excellent electrical and thermal conductivities, low viscosity, and low toxicity, making them ideal for creating highly stretchable and conductive composites suitable for flexible electronic devices. Despite these benefits, conventional single-layer liquid metal composites face challenges, such as liquid metal leakage during deformation (e.g., stretching or bending) and limited elongation due to incomplete integration of the liquid metal within the elastomer matrix. To address these limitations, we introduced a bilayer structure into liquid metal composites, comprising a lower polydimethylsiloxane (PDMS) layer and an upper PDMS-liquid metal mixed layer. In the mixed layer, the liquid metal precipitates, forming a conductive network spanning both layers. This bilayer composite structure demonstrated significantly improved stretchability and elongation compared to pure PDMS or single-layer composites. Additionally, by adjusting the size and content of the liquid metal particles, we optimized the composite’s mechanical and electrical properties. Under optimal conditions, spherical liquid metal particles deform into elliptical shapes under tensile stress, increasing conductive pathways and reducing electrical resistance. The combined effects of the bilayer structure and particle shape deformation enhanced the composite’s stretchability and elongation, supporting its potential for flexible electronics applications.

Electroencephalography (EEG) electrodes require low impedance, high biocompatibility, and long-term performance. Conventional Ag/AgCl wet electrodes achieve low impedance but suffer from dehydration and skin irritation, whereas dry electrodes often induce discomfort or exhibit high impedance. To address these limitations, this study engineered a hydrogel-based electrode by incorporating PEDOT:PSS and the nonionic surfactant Triton X-100 into an acrylic acid hydrogel matrix. The flexible acrylic acid backbone, conductive PEDOT:PSS domains, and the nanofibrillar network promoted by Triton X-100 simultaneously enhanced mechanical compliance and electrical stability. In addition, the structural rearrangement of PEDOT:PSS was verified through morphological analyses. The fabricated electrode exhibited a modulus comparable to human soft tissue, demonstrated strong interfacial adhesion in shear tests, and significantly reduced skin–electrode contact impedance. Furthermore, EEG measurements showed that the hydrogel electrode achieved alpha- and beta-band signal power comparable to commercial Ag/AgCl electrodes. These findings establish the PEDOT:PSS–Triton X-100 hydrogel electrode as a promising candidate to replace conventional wet and dry electrodes for reliable EEG applications.

Compression and tension sensors with a porous structure have attracted attention recently. Porous sponge sensors have the advantage of a wide deformation range owing to their structural characteristics. In this study, a porous sponge structure was prepared by absorbing polydimethylsiloxane (PDMS) into the matrix of porous commercial sugar cubes. A conductive network was formed by coating the outside of the sponge skeleton with silver nanowires (AgNWs), which have a high aspect ratio. In addition, a liquid metal (LM), which does not directly form an electrical network but changes from zero-dimensional to one-dimensional under an external force was introduced into this porous sponge structure. The effects of the LM on the sensor sensitivity to pressure and strain were analyzed by comparing the electrical resistance changes of PDMS/AgNW and LM/PDMS/AgNW sponge sensors under tension and pressure. This study shows that the use of a porous structure and an LM may be useful for future wearable sensor design.

The transition metal dichalcogenide (TMDC) NbSe₂ is a highly conductive and superconducting material with great potential for next-generation electronic and optoelectronic devices. However, its bulk form suffers from reduced charge density and conductivity due to interlayer van der Waals interactions. To address this, we exfoliated NbSe₂ into nanosheets using lithium-ion intercalation and utilized them as diaphragms in acoustic transducers. Conventional electromagnetic and electrostatic mechanisms have limitations in sound pressure level (SPL) performance at high and low frequencies, respectively. To overcome this, we developed a hybrid force mechanism combining the strengths of both approaches. The NbSe₂ nanosheets were successfully prepared and analyzed, and the NbSe₂-based hybrid acoustic transducer (N-HAT) demonstrated significantly improved SPL performance across a wide frequency range. This study offers a novel approach for designing high-performance acoustic devices by harnessing the unique properties of NbSe₂.