UV-assisted coaxial DIW 3D printing: a strategy for fabricating environmentally adaptive ionic hydrogel sensors
Ionic conductive hydrogels have gained extensive attention in the field of intelligent sensing due to their good flexibility, tunable electrical conductivity, and multi-stimuli responsiveness. However, hydrogels easily freeze, dehydrate or swell in external environments, and thus losing their original structure and functions. Therefore, improving the environmental adaptability of conductive hydrogels remains a challenge. Herein, ionic hydrogels were encapsulated in real time via UV-assisted multi-material coaxial direct ink writing (DIW) 3D printing, and ionic conductive hydrogel sensors with array structures were prepared. The core ionic conductive hydrogel is isolated from the external environment by the hydrophobic photocurable polydimethylsiloxane (PDMS) shell resin. The PDMS shell resin isolates the core hydrogel from moisture and heat in the external environment, thereby significantly enhancing the sensor’s stability. After 60 days of storage at 25 °C, the 3D-printed coaxial array sensor exhibits only 2.5% mass loss; when stored underwater for 60 days, its swelling rate is merely 1.5%. This sensor exhibits high strain sensitivity with a gauge factor (GF) up to 1.705 and good cyclic stability, demonstrates stable operation over a wide temperature range of -20°C to 120°C, and can withstand underwater and solvent environments. It has been successfully applied in various scenarios such as human motion monitoring, underwater sensing, and temperature sensing. This research breaks through the environmental limitations of conventional hydrogel sensors and provides a simple, efficient method for developing flexible sensors with high environmental adaptability.