Direct construction of strong, tough, conductive, and adhesive hydrogel bioelectronics enabled by salt-dissolved cellulose

Abstract

Long-active mechanical toughness, conductivity, and adhesiveness are essential in the applications of hydrogel bioelectronics. Existing approaches usually integrate different functional materials into one system to endow hydrogels with desired properties, which tends to suffer from poor compatibility, cumbersome operations, and unsustainable processes, seriously limiting their real-world applications. Herein, we report a one-step strategy for directly constructing polyacrylic acid/cellulose (PAA/Cel) ionogels with a combination of strong, tough, conductive, and adhesive properties by adding ZnCl2-dissolved cellulose in a facile, efficient, and environmentally friendly manner. The introduction of salt-dissolved cellulose can simultaneously realize the all-round improvement of the ionogel in terms of mechanics, conductivity and adhesion. Particularly, for the PAA/Cel-20 % ionogel, it has a 3.3-fold higher compressive strength (18.8 MPa vs. 4.4 MPa), a 17.2-fold higher fracture toughness (154.0 kJ m−3 vs. 8.5 kJ m−3), a 5.5-fold higher interfacial toughness (247.3 J m−2 vs. 45.0 J m−2), a 4.0-fold higher shear strength (394.5 kPa vs. 78.6 kPa), and a 29.9-fold higher ionic conductivity (74.1 mS m−1 vs. 2.4 mS m−1) compared to the PAA hydrogel. These improved mechanical and adhesive behaviors are due to the synergistic enhancement effect of the compact hydrogen bonds formed between the carboxyl groups (–COOH) of PAA and the hydroxyl groups (–OH) of Cel, as well as the coordination interactions produced by Zn2+ and –COO− for PAA. The observed increase in ionic conductivity is attributed to the presence of abundant dissociated active ions including Zn2+ and Cl−. Our resulting ionogel enables electrophysiological signals to be reliably recorded with high signal-to-noise ratios when assembled as bioelectronics for use in monitoring body movements. The strategy presented here facilitates the development of high-performance adhesive ionogels and could go beyond for bioelectronics in medical monitoring systems.