Breathable and conductive polyvinyl alcohol/carboxymethyl chitosan hydrogels prepared via a template strategy for flexible sensors.

Abstract

Flexible electronic sensors have garnered significant interest in applications spanning epidermal electronics, soft robotics, and next-generation wearable systems. This work reports a novel fabrication strategy for a breathable, strain-sensitive conductive hydrogel (PCH) that integrates high electrical conductivity, superior mechanical compliance, and enhanced wearing comfort. The hydrogel matrix comprised a conductive double-network structure formed from polyvinyl alcohol (PVA), carboxymethyl chitosan (CMC), hydroxypropyl cellulose (HPC), and a hydrophilic nanocomposite of hydroxylated carbon nanotubes and nanocellulose (OHCNT-CNF), with NaCl serving as an ionic dopant. A precisely controlled, perforated, and continuously tunable porous architecture was engineered using AgCl as a templating agent. PVA constituted the primary network, endowing the hydrogel with elasticity, flexibility, and soft tactile properties. CMC and HPC jointly formed the secondary dynamic network, significantly enhancing toughness, tensile strength, and structural stability under cyclic deformation. Moreover, the abundant surface hydroxyl groups on CMC and HPC fibers promoted preferential ion accumulation within water-rich porous domains, thereby facilitating efficient ionic conduction pathways. Synergistic contributions from the OHCNT-CNF nanocomposites and NaCl further elevated bulk conductivity. The PCH porous hydrogel demonstrated excellent conductivity (6.38 S/m), breathability (15.34 mg cm-2 h-1) and high sensing sensitivity (GF = 2.66). It enabled highly sensitive, real-time monitoring of a broad range of human motions and physiological signals, including electromyography (EMG) and electrocardiography (ECG). By virtue of its sensitive monitoring of EMG, the PCH hydrogel was applied to human-machine interaction systems, realizing real-time, high-precision manipulation of a robotic arm and virtual characters in electronic games.