Multifunctional conductive hydrogels for wearable sensors and supercapacitors

Abstract

Conductive hydrogels have attracted extensive attention in the field of flexible electronics due to their excellent biocompatibility, suitable Young's modulus, and outstanding electrical conductivity. However, the inherent water-rich feature and insufficient interfacial adhesion of hydrogels hinder the stability and reliability of hydrogel-based devices for applications in complex environments. Herein, we design a novel polyacrylamide/polydopamine hydrogel using deep eutectic solvent (DES) and alkaline solution as the polymerization medium, and the as-obtained hydrogel has both self-adhesive (20.20 kPa for tissue) and anti-freezing properties (−20 °C). The combination of DES and alkaline solution replaces pure DES, which provides the conditions for oxidative polymerization of dopamine to ensure the adhesion performance of the hydrogel and also makes the hydrogel retain the conductivity and low melting point characteristics of DES. Furthermore, biocompatible carboxylated cellulose nanofibers (CCNFs) are embedded into the hydrogel to further enhance the mechanical properties by about 3 times through non-covalent interactions, physical entanglement and friction between CCNFs and the polymer. Remarkably, the hydrogel can be adhered to the skin as a bioelectrode for electrocardiography and can be used as a strain sensor to monitor human movements even after storing for 15 days at −20 °C. Meanwhile, the electrochemical characterization of supercapacitors using this hydrogel as an electrolyte shows great application potential.