Chitosan-based self-healing, adhesive and anti-swelling hydrogel for wearable flexible strain sensor

In recent years, hydrogel has become favorable choice for sensor substrate materials due to its decent flexibility and biocompatibility. Ideal hydrogels with self-healing property are considered to extend the service life of hydrogel-based sensors. And the durability of hydrogel is also largely dependent on environmental stability, especially in high humidity and underwater environments. Herein, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogels with self-healing behavior under diverse environmental conditions could be fabricated with chitosan (CS), vanillin, acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA) and [2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA). Owing to the formation of Schiff base bonds, electrostatic interactions and hydrogen bonds and the hydrophilic-hydrophobic chain segments balance, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel demonstrated decent anti-swelling performance and excellent mechanical properties in amphibiotic environment. Moreover, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel exhibited self-healing property in a wide range of environments including corn oil, seawater and low-temperature condition, which held great significance for broadening the application scope of hydrogel. In addition, the hydrogel displayed adhesion property, which could be attributed to carboxyl, hydroxyl, amino, quaternary ammonium and sulfonic acid groups of the hydrogel. As a result, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel could adhere to the surface of substrates through Schiff base bonds, metal coordination bonds, electrostatic interactions and hydrogen bonds. Meanwhile, CS/Vanillin-P(AA-co-HEMA)/SBMA hydrogel also exhibited outstanding electrical conductivity due to the introduction of SBMA. Therefore, the prepared multifunctional hydrogel was employed as hydrogel-based wearable strain sensor, which could sensitively detect various human movements, especially in underwater environments. It could be anticipated that the designed hydrogel holds significant potential in the domain of wearable strain sensors.