Photocurable Nanocellulose-Based Hydrogel for Real-Time Electrochemical Sweat Monitoring in Smart Textiles

Wearable sweat sensors demand hydrogels that wet textiles rapidly, cure on demand, and retain mechanical integrity during use. In this work, a UV-curable poly(acrylic acid)/cellulose nanocrystal (PAA/CNC) hydrogel was developed to improve the performance and reliability of flexible electronic sensing systems. The formulation gels within about 2 to 4 s across the series and forms a uniform network suitable for scalable coating and patterning. CNCs simultaneously enhance hydrophilicity and mechanical robustness: the static contact angle decreases from 37.1° at 0 wt % CNC to 9.9° at 10 wt % CNC, while the equilibrium swelling ratio peaks at 657% for 8 wt % CNC and remains high at 650% for 10 wt % CNC, balancing hydrations with dimensional stability. Bulk properties improve with CNC loading, with maximum tensile strength increasing from 133 to 180.7 kPa and Young's modulus from 0.73 to 1.25 MPa, followed by a modest plateau beyond about 5 to 8 wt % that is consistent with emerging filler-filler interactions. FTIR indicates esterification between PAA and CNC, and SEM reveals a continuous porous morphology favorable for ion transport. Overall, the 10 wt % CNC formulation maximizes stiffness and strength while maintaining good hydrophilicity and rapid photocuring behavior. These attributes position photocured PAA/CNC hydrogels as promising matrices for textile-integrated, impedance-based sweat sensing.