Highly Strong, Tough, and Stretchable Conductive Hydrogels Based on Silk Sericin-Mediated Multiple Physical Interactions for Flexible Sensors

The development of hydrogel-based electronic sensors integrated with excellent mechanical performance, conductivity, high sensitivity, and stability is still a great challenge. In this work, a highly strong, tough, and stretchable conductive hydrogel was proposed using silk sericin (SS), polyvinyl alcohol (PVA), and sodium citrate (Na(3)Cit) via combining freeze-thaw with the salting-out route. SS with rich-binding sites (-COO-, -NH2, and -OH) was exploited to construct an ionic conductive hydrogel with multiple physical interactions containing hydrogen bonds, ionic coordinations, and hydrophobic interactions. The obtained composite hydrogels (PVA/SS/Na(3)Cit) displayed a prominent tensile strength of 4.42 +/- 0.32 MPa, an elastic modulus of 3.14 +/- 0.26 MPa, a toughness of 13.73 +/- 1.05 MJ/m(3), and an excellent stretchability (>500% of strain) and self-recovery. In addition, the introduction of SS not only mediated the noncovalent cross-link network but also enabled excellent ionic conductivity of the hydrogels due to the coordination effect of Na+ and Cit(3-) ions. Moreover, the PVA/SS/Na(3)Cit conductive hydrogels can be used as a strain sensor to monitor human activities, and they exhibit a wide work range, good sensitivity, and stability, suggesting promising applications in flexible and stretchable wearable electronics.