Conductive hydrogel based on dual-ion enhanced carboxymethyl chitosan and 3D printing for wearable sensors

As a core component of wearable devices, flexible sensors remain limited by the challenge of simultaneously optimizing their mechanical strength, sensing sensitivity, and strain range. In this study, an ion-conductive double-network hydrogel was developed using direct ink writing (DIW) three-dimensional printing technology. The hydrogel was synthesized via a one-pot method using carboxymethyl chitosan, N-acryloyl glycinamide, and methyl cellulose, and then sequentially soaked in Fe³⁺ and Li⁺ solutions to form a dual crosslinked network composed of covalent bonds and coordination/hydrogen bonds. The resulting hydrogel exhibited high stretchability (breaking elongation of 418.56%), excellent toughness (1175.53 KJ/m³), strong fatigue resistance (stable stretching for 12 cycles at 150% strain and stable compression for 30 cycles at 50% strain), high ionic conductivity (3.38 mS/cm), and excellent anti-swelling, antioxidant, and biocompatibility. Furthermore, we fabricated sensors with various topologies (triangle, honeycomb, and concentric) using DIW. Among them, the triangle sensor demonstrated high sensitivity (gauge factor up to 10.08), fast response (463 ms), a wide detection range (0-400%) and reliable monitoring of multiscale human physiological activities and underwater motion. Additionally, the sensor showed potential for information encryption and signature recognition. This study provides an integrated materials-to-structure strategy for developing next-generation high-performance and customizable flexible electronic devices.