A UV-filtering, environmentally stable, healable and recyclable ionic hydrogel towards multifunctional flexible strain sensor

To meet the requirements of various practical applications and enhance the human experience, multifunctional hydrogel sensors are of great significance for flexible wearable devices. However, it remains a great challenge to fabricate an integrated multifunctional composite hydrogel sensor combining high strength, transparency, UV filterability, environmental stability, self-healing and easy recyclability via a simple method for multi-field applications. In this paper, tannic acid-coated cellulose nanocrystals (TA@CNC) were incorporated into polyvinyl alcohol/gelatin/ethylene glycol/Al3+ hydrogel to prepare a multifunctional composite ionic hydrogel (PGETA) by a one-step freeze-thaw method. The stable dispersibility problem of Al3+ in binary solvents was solved by introducing TA@CNC. The prepared PGETA hydrogel showed high tensile strength (1.95 MPa), stretchability (519.7%), high transparency (>80%), great UV-filtering property, favorable low-temperature tolerance (-20 degrees C) and superior moisturizing performance (30 days). Moreover, the completely reversible dynamic hydrogen bonding and ionic coordination interaction provided the PGETA hydrogel with good self-healing capability and easy recyclability. The PGETA ionic hydrogel strain sensor could be employed as wearable device to monitor large deformations as well as subtle physiological signals in different body parts at room or low temperature. The novel PGETA hydrogel holds great promise for applications in electronic skin and wearable devices, and the strategy will shed light on preparation of a multifunctional hydrogel sensor for broad applications.