Flexible wearable sensors based on multifunctional carboxymethylcellulose/polyacrylamide/gelatin hydrogels: Collaborative design of high-sensitivity monitoring and visual feedback.

Creating flexible hydrogels that combine high mechanical strength, conductivity, and functionality remains a challenge. Sodium carboxymethyl cellulose (CMC) was successfully added to a double network composite hydrogel based on polyacrylamide (PAM)/gelatin, resulting in a synergistic improvement in visualization, excellent mechanical properties (stress = 0.458 MPa, strain = 946 %, toughness = 1.97 MJ/m3), strong self-adhesion (adhesion strength = 6.21-8.91 kPa), and a broad range of sensitive conductivity (GF = 2.42-7.21, response time = 210 ms). It also demonstrated potential for dynamic anti-counterfeiting. Results showed that adding CMC increased the hydrogel's suitability for visualization and significantly boosted its mechanical properties, enabling it to be both conductive and strain-sensitive. This makes it suitable for monitoring human movements and emotional changes. Additionally, the hydrogel displayed universal self-adhesive properties, allowing it to adhere stably to human skin and accurately track large joint movements and micro-expressions. For further functionality, the hydrogel's transparency was enhanced by ionic crosslinking through immersion in CaCl₂ solution, and its dynamic optical response offers new possibilities for anti-counterfeiting. The combined use of CMC and ion regulation overcomes the usual trade-offs between mechanical strength, conductivity, and visualization in traditional hydrogels. This creates a high-performance material platform for next-generation multifunctional flexible wearable sensors and paves the way for advances in human-computer interaction, flexible electronic skin, and visual sensors.