Tough ion-electron conductive hydrogels with multi-crosslinked network for strain sensors

Abstract

Conductive hydrogels, due to their flexibility and conductivity, offer potential for wearable bioelectronics. Enhanced conductivity in these hydrogels stems from the conducting network of reactive particles, notably polypyrrole (PPy). Nevertheless, the hydrophobicity, brittleness, and opacity of conjugated π PPy hinder its application in conducting hydrogels for flexible, wearable, and transparent electronics. Herein, PPy-decorated cellulose nanocrystals (CNC-PPy) hydrophilic complexes are initially synthesized by in situ polymerization of pyrrole (Py) onto CNC. Subsequently, an ion-electron conductive PCPF hydrogel with a multi-crosslinked network structure is developed using polyvinyl alcohol bearing styrylpyridinium group (PVA-SbQ) and CNC-PPy under UV irradiation and ammonium persulfate (APS)-induced gelation, followed by ferric chloride (FeCl₃) immersion. APS both initiates polymerization and disrupts PPy π-π stacking, enhancing mechanical properties and transparency. The unique synergy effect of CNC-PPy and FeCl₃ contribute to superior mechanical (tensile strength of 370 ± 17 KPa and elongation at break of 702 ± 18 %), electrical (4.50 mS.cm^-1) and strain sensitivity (GF = 1.43). Furthermore, it effectively monitors large deformations, like joint bending, and small deformations such as pulse. Thus, our approach offers a promising strategy for developing PVA-based hydrogels with exceptional mechanical and electrical properties while maintaining transparency, rendering them ideal for flexible sensors.