Rapid self-healing, self-adhesive, anti-freezing, moisturizing, antibacterial and multi-stimuli-responsive PVA/starch/tea polyphenol-based composite conductive organohydrogel as flexible strain sensor

The complexity of application environment stimulates the development of wearable devices based on functional hydrogels. Among all the promising performances, self-healing and self-adhesion properties are ideal for hydrogel sensors, which can guarantee good accuracy, comfort and long service life. However, it is still a challenge to achieve simultaneous self-healing and self-adhesion in different environments (in the air, underwater and at low temperatures). Herein, a feasible new strategy was successfully carried out to prepare a starch-based composite conductive organohydrogel based on the reversible borate ester bonds formed by complexing starch/polyvinyl alcohol (PVA)/tea polyphenol (TP) with borax, and multiple hydrogen-bond interactions among PVA, starch, TP and ethylene glycol (EG). Silver nanoparticles (AgNPs), reduced and stabilized by TP, and MWCNTs (multi-walled carbon nanotubes) were introduced into the cross-linking networks to endow the resulting PBSTCE organohydrogel with considerable antibacterial property and conductivity, respectively. The organohydrogel possessed rapid self-healing (HE (self-healing efficiency) = 96.07% in 90 s, both in the air and underwater, also at -20 °C), considerable self-adhesion (both in the air and underwater, also at -20 °C), remarkable stretchability (814% of elongation), anti-freezing (-20 °C) and moisture-retention abilities, antibacterial activity, sensitive pH/sugar-responsiveness, and plasticity. The strain sensor formed by the PBSTCE organohydrogel can not only effectively record large-scale human motions (e.g. finger/wrist/elbow bending, walking, etc.), but also accurately capture subtle motion changes (e.g. breathing, chewing, swallowing, speaking, smiling and frowning). Moreover, the self-healed organohydrogel sensor also exhibited almost invariable mechanical, electrical and sensing behaviors. This work demonstrates a feasible strategy to construct multifunctional starch-based organohydrogels, and promotes their efficient, stable and eco-friendly application as flexible wearable devices.