Modulation of Hydration and Charge Transport Conductive Hydrogels for Soft Skin-Attachable Sensor

Abstract

In hydrogel-based soft bioelectronic materials, the key factors that determine performance are the water structure within the polymer network, ion interactions, and the stability of conductive pathways. Water content acts as a critical factor that simultaneously regulates the mechanical behavior and electrical properties of hydrogels, while ion–polymer interactions directly influence the structural stability and functional retention of the network. However, in conventional conductive hydrogels, there are limitations in stably controlling these factors simultaneously. Therefore, an integrated design strategy that can simultaneously satisfy water retention, mechanical stability, and electrical conductivity is required. To address this, this study combines the hydration and water-stabilizing effects of lithium ions (Li⁺) with the charge-transport properties of the conductive polymer poly(3,4-ethylenedioxythiophene):polystyr ene sulfonate and applies them to a polyacrylamide (PAAm)–alginate double-network structure. This design aims to stabilize the water structure within the polymer matrix. The fabricated hydrogel exhibits mechanical stretchability of up to 310%, while maintaining stable conductivity under repeated mechanical deformation. It retains 81.8% of its initial mass after 24 h of air exposure, which demonstrates excellent water-retention capability. Furthermore, the hydrogel was successfully demonstrated as a motion sensor capable of detecting human joint movements with fast and reproducible electrical responses, which indicates its potential for wearable bioelectronics.