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.