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

Abstract

• A novel PVA/starch/tea polyphenol-based conductive organohydrogel is fabricated. • Organohydrogel contains dynamic borate ester bonds and reversible multiple hydrogen bonds. • Organohydrogel features its remarkable self-healing and self-adhesive properties in the air, underwater and at low temperature. • Organohydrogel exhibits anti-freezing, moisturizing, antibacterial and pH/sugar-responsive properties. • Organohydrogel as strain sensor can accurately monitor various human motions and vital signs. 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.