Zwitterionic Surfactant Enhanced Stable Hydrogels for Epidermal Sensors and External Contact Object Perception

Hydrogel-based epidermal sensors are highly valued for their flexibility, biocompatibility, and ability to monitor physiological signals with high fidelity. However, their widespread application has been hindered by challenges related to stability and low conductivity, which can degrade performance over time. In this study, we present a novel approach to enhance both the stability and conductivity of hydrogels while maintaining biocompatibility by incorporating betaine (BA) into ionically conductive acrylamide (AA) and poly(2-acryloylamino-2-methyl-1-propanesulfonic acid) (AMPS) hydrogel matrices. The incorporation of the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) addresses the conductivity reduction caused by excessive BA, restoring high ionic conductivity (∼0.84 S m^-1) of the hydrogel. As a result, the hydrogel demonstrates excellent stability, retaining 78% of its weight after 14 days, while maintaining exceptional electrical, mechanical (∼18.13 kPa tensile strength, ∼450% elongation), and adhesive (∼4.01 kPa) properties. This optimized hydrogel enables reliable epidermal sensing, ensuring high-quality electrophysiological signal acquisition (signal-to-noise ratio ∼ 25 dB) unaffected by motion artifacts and achieving 97.5% accuracy in external object contact sensing, presenting a promising solution for the development of advanced wearable electronics.