Stretchable Dry Adhesives for Robust Epidermal Biosignal Sensing

Conformal skin-electrode contact is crucial for acquiring high-quality multimodal biosignals from the uneven human epidermis. Although stretchable dry adhesives (SDAs) are promising solutions, their development is hindered by the low stretchability and high hygroscopicity of biocompatible adhesive materials. Here, the study reports highly stretchable, nonhygroscopic, and biocompatible SDAs developed through the synergistic effects of tannic acid and polyol compounds. These SDAs exhibit a high crack onset strain (ε_c ≥ 50%) and strong adhesive force (>0.7 N cm^-1) under various humidity conditions. When integrated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based stretchable transparent electrodes (STEs), the SDA/STE bilayer forms bumpy interfaces with the swelling of STEs during SDA casting, enabling strong adhesion and efficient biosignal acquisition. The conformal and long-term stable skin-electrode contact provided by these SDAs is further demonstrated in a wearable device used for overnight sleep stage analysis. Notably, the results from the wearable device are comparable with those of conventional polysomnography conducted in clinical settings. With their ultrathin, transparent, and lightweight design, the SDA/STE electrodes offer a pathway toward the commercialization of user-friendly wearable devices for daily health monitoring.