Skin-mimicking strategy to fabricate strong and highly conductive anti-freezing cellulose-based hydrogels as strain sensors.

Conductive hydrogels have attracted increasing attention for applications in wearable and flexible strain sensors. However, owing to their relatively weak strength, poor elasticity, and lack of anti-freezing ability, their applications have been limited. Herein, we present a skin-mimicking strategy to fabricate cellulose-enhanced, strong, elastic, highly conductive, and anti-freezing hydrogels. Self-assembly of cellulose to fabricate a cellulose skeleton is essential for realizing a skin-mimicking design. Furthermore, two methods, in situ polymerization and solvent replacement, were compared and investigated to incorporate conductive and anti-freezing components into hydrogels. Consequently, when the same ratio of glycerol and lithium chloride was used, the anti-freezing hydrogels prepared by in situ polymerization showed relatively higher strength (1.0 MPa), while the solvent-replaced hydrogels exhibited higher elastic recovery properties (94.6 %) and conductivity (4.5 S/m). In addition, their potential as strain sensors for monitoring human behavior was analyzed. Both hydrogels produced reliable signals and exhibited high sensitivity. This study provides a new horizon for the fabrication of strain sensors that can be applied in various environments.

A skin-inspired biomimetic strategy to fabricate cellulose enhanced antibacterial hydrogels as strain sensors.

With the development of wearable devices, the fabrication of strong, tough, antibacterial, and conductive hydrogels for sensor applications is necessary but remains challenging. Here, a skin-inspired biomimetic strategy integrated with in-situ reduction has been proposed. The self-assembly of cellulose to generate a cellulose skeleton was essential to realize the biomimetic structural design. Furthermore, in-situ generation of silver nanoparticles on the skeleton was easily achieved by a heating process. This process not only offered the excellent antibacterial property to hydrogels, but also improved the mechanical properties of hydrogels due to the elimination of negative effect of silver nanoparticles aggregation. The highest tensile strength and toughness could reach 2.0 MPa and 11.95 MJ/m3, respectively. Moreover, a high detection range (up to 1300%) and sensitivity (gauge factor = 4.4) was observed as the strain sensors. This study provides a new horizon to fabricate strong, tough and functional hydrogels for various applications in the future.