Transparent and Stretchable Conductive Hydrogel Sensors: Optimizing Ion Selection to Enhance Mechanical and Sensing Performance

Conductive hydrogels, with their unique combination of electrical conductivity and stretchability, are emerging as critical components for next-generation, flexible, and wearable sensors. In this work, we aimed to develop a low-cost, easy-to-manufacture hydrogel sensor using ionic compounds as the source of conductivity. Hydrogels were synthesized using acrylamide, poly(ethylene glycol), and carboxymethyl cellulose, with systematic variation of ionic compounds LiCl, NaCl, and KCl, labeled as Li-CH, Na-CH, and K-CH, respectively, to explore their effects on the nanostructure and mechanical properties of the hydrogels. Among the different formulations, Na-CH demonstrated superior performance with optimized elongation at break, tensile strength, and toughness, highlighting the importance of ion selection in hydrogel design. Na-CH also exhibited excellent stretchability, outstanding transparency, and high sensitivity in detecting a wide range of body movements, from large-scale gestures to subtle physiological signals such as pulse detection. With its exceptional combination of transparency, mechanical robustness, and repeatable sensing performance, Na-CH shows great potential for future applications in flexible electronics, healthcare monitoring systems, and smart display technologies.