Carboxymethyl cellulose-reinforced sandwich-structured carbon nanotube composite hydrogels for strain sensing and joule heating

Conductive hydrogels hold significant promise for wearable electronics, yet achieving a balance between excellent stretchability and high electrical conductivity remains challenging. To address this, we developed a sandwich-structured hydrogel using carboxymethyl cellulose (CMC)-reinforced polyacrylamide (PAM) as the matrix hydrogel, with surface-deposited carbon nanotubes (CNTs). CMC plays a dual role in the composite hydrogels. Its functional groups form hydrogen bonds with PAM, significantly enhancing mechanical properties (106.38 kPa stress, 637.25 % strain). Additionally, pre-crosslinking with hydroxylated CNTs ensures uniform dispersion while strengthening interfacial adhesion to the hydrogel surface. Subsequent dehydration densifies the CNT layer, improving both tensile properties and electrical conductivity. The hydrogel exhibits 806.94 % strain at a 150 % water-solid ratio and a 31.9 S/m electrical conductivity at a 100 % water-solid ratio. The resulting CPam-CNT hydrogel demonstrates exceptional performance as a high-sensitivity strain sensor ( GF  = 19.662 under 0–60 % strain), with rapid response/recovery times (20/40 ms) and outstanding stability for real-time human motion monitoring. Concurrently, the conductive CNT layer enables efficient Joule heating, achieving rapid temperature elevation (100 °C from room temperature within 2 min) with stable thermal cycling. This work introduces an integrated strategy for multifunctional hydrogels combining sensitive strain sensing and controllable Joule heating, advancing their potential in wearable applications.