UV-curable gelatin/carboxylated CNT conductive hydrogels: a versatile platform for flexible strain sensor applications

Developed stepwise modification strategy for UV-curable gelatin-based conductive hydrogels. • Optimized water/glycerol solvent system to achieve outstanding long-term moisture retention. • Constructed hybrid ionic-electronic networks via carboxylated CNT reinforcement. • Demonstrated stable wide-range strain sensing for wearable human motion monitoring. Conductive hydrogels serve as core matrix materials for flexible strain sensors, but conventional hydrogels suffer from rapid water loss under ambient conditions and an inherent trade-off between mechanical and conductive properties. This work develops a gelatin/poly(acrylic acid) composite conductive hydrogel synergistically functionalized with glycerol for moisture retention, aluminum salts for ionic crosslinking, and carboxylated multi-walled carbon nanotubes (c-MWCNTs) for reinforcement. Moisture retention is optimized by tuning the water-to-glycerol ratio, and three aluminum salts are compared to identify the optimal crosslinker. Multi-dimensional characterizations reveal interfacial interactions and microstructural evolution, and the regulatory effect of c-MWCNTs loading on electromechanical and sensing properties is systematically investigated. At a water-to-glycerol ratio of 50:50, the hydrogel retains over 82% water after 7 days of ambient storage. The aluminum chloride system exhibits the optimal ionic conductivity and balanced mechanical performance. With 0.025 wt% c-MWCNTs uniformly embedded via hydrogen bonding and coordination interactions, both conductivity and tensile toughness are significantly enhanced. The resulting flexible strain sensor features stable sensitivity over a wide strain range and excellent fatigue resistance, enabling accurate monitoring of human joint motions and showing great potential for wearable health monitoring. Download: Download high-res image (220KB) Download: Download full-size image