Multifunctional Conductive Hydrogel Sensors for Multiscale Motion Detection and Wide-Range Temperature Monitoring

Abstract

Conductive hydrogels, with their remarkable flexibility, electrical conductivity, sensitivity, and skin-compatible elastic modulus, have emerged as a promising material for advanced flexible wearable sensors. Nevertheless, the majority of conductive hydrogels are primarily designed for strain sensors to monitor human motion, lacking additional functionalities, such as temperature responsiveness. Moreover, the rich water composition in hydrogels makes them susceptible to freezing at low temperatures, leading to a loss or reduction in functionality, which greatly hinders their practical application in wearable electronics. Herein, a highly sensitive strain and temperature dual-responsive hydrogel sensor (SA-PBAD@PHEAA) with exceptional performance was successfully fabricated. The hydrogel uses sodium alginate (SA) and pyridine-4-boronic acid derivatives (PBAD) for a dynamic boronic acid ester network and poly(N-(2-hydroxyethyl)acrylamide) (PHEAA) for a second network. In addition, a mixed solution of choline chloride (ChCl) and glycerol as well as KCl are added to enhance its overall performance. The resulting hydrogel exhibits remarkable properties, including high toughness (6.00 MJ/m3), excellent tensile properties (6570%), superior electrical conductivity (13.62 mS/cm), high strain response sensitivity (GF = 5.17), high transparency (95.7%), fast response (104 ms, 100 ms), tissue softness (elastic modulus: 0.05 MPa), and strong adhesion (157.8 kPa to paper). The hydrogel sensor enables simultaneous detection of tensile strain (gauge factor: 5.17) and temperature (temperature coefficient of resistance: 3.48%/°C) with high sensitivity, covering a broad range (−70 to 80 °C) and maintaining stability, especially at low temperatures. This study presents an efficient approach for the development of multifunctional hydrogels and expands their applications in a human-computer interface and soft robot.