High-performance ionic conductive poly(vinyl alcohol) hydrogels for flexible strain sensors based on a universal soaking strategy

Abstract

Conductive materials with predominant mechanical properties and high sensitivity have promising applications in various fields such as fabrication of electric skins, wearable sensors, and soft robotics. High-performance and flexible strain sensors based on conductive hydrogels have attracted significant attention because of their potential applications in voice recognition and human–machine interfaces. Inspired by the mechanism of neural tissue signal transmission, herein, a high-strength and relatively high-sensitivity ionic conductive hydrogel was developed by utilizing the completely physically crosslinked polyvinyl alcohol (PVA) and a simple inorganic salt solution soaking strategy. The ionic conductive hydrogels exhibited intriguing remoldability and excellent mechanical properties such as superb tensile strength (8.03 MPa), high toughness (28.7 MJ m⁻³), and high elastic modulus (1 MPa) because of their high-density hydrogen bonding and chain entanglement networks. By integrating the PVA–NaCl gel into a flexible strain sensor, the sensor displayed high conductivity (7.14 S m⁻¹) at room temperature and subzero temperature, high accuracy (GF = 0.989), and sensitive strain responsiveness in a wide strain detection window of 0.2–400%. These results imply good performance for monitoring and distinguishing various human daily activities and slight physiological signals. Furthermore, the as-made PVA sol could convert to gel state just by being injected on a flexible substrate under an ice-bath and the conductive hydrogels displayed excellent biocompatibility and improved cell proliferation. Therefore, the as-formulated hydrogel sensor can have promising applications in wearable devices, such as sports monitoring, healthcare monitoring or voice recognition.