Cellulose nanocrystal reinforced conductive hydrogels with anti-freezing properties for strain sensors

Hydrogels have been considered one of the most promising materials for high-sensitivity sensors to instantaneously detect human physiological activities. However, fabricating a flexible hydrogel combining toughness, ionic conductivity, and anti-freezing capability is still a challenge. In this work, new interpenetrating polymer network (IPN)-structured hydrogels with stretchable, tough, and conductive properties were fabricated based on chemical cross-linked poly(acrylic acid) and physically cross-linked poly(vinyl alcohol). The introduction of cellulose nanocrystal (CNC) chains significantly enhanced the tensile strength and toughness. In particular, the introduction of the ethylene/water binary solvent maintained its original flexibility even after 24 hours of freezing at −20 °C. In addition, the developed hydrogel-based sensor was capable of differentiating accurately large and small movements of the human body, such as limb rotation, finger bending, and heartbeat.