Advanced In-Situ functionalized conductive hydrogels with high mechanical strength for hypersensitive soft strain sensing applications

Abstract

Conductive hydrogels are used in wearable electronics, soft robotics and artificial skin due to their flexibility, biocompatibility and multifunctionality. However, combining high mechanical strength, conductivity and sensitivity in these hydrogels remains a challenge. This paper proposes a novel in-situ conductive functionalization technology for hydrogels with high mechanical strength, achieving high conductivity (3223.727 S·m−1) and low resistance (0.92 Ω) without sacrificing mechanical properties. Comprehensive experiments reveal the mechanisms and optimal parameters for conductive functionalization. AgNO3 and ascorbic acid (VC) concentrations influence the distribution, reaction rate and aggregation of Ag particles on hydrogel surfaces. Sodium carboxymethylcellulose (CMC) enhances mechanical strength and Ag+ adsorption capacity. Optimal parameters are 1.00 M AgNO3 and 0.08 M VC. An in-situ reduction reaction of silver particles establishes strong interfacial bonding between the silver layer and hydrogel matrix, forming the basis for strain sensing. The hypersensitized sensing mechanism, involving the appearance and recovery of microcracks on the silver layer via the tunneling effect, enables high sensitivity (gauge factor = 36.65). The conductive hydrogels can monitor human physiological signals, tiny strain signals from water droplets (0.01 g) and airflow, with an average response time of 12.7 ms. The developed conductive hydrogels meet the technical requirements for combining high mechanical strength and sensitivity, offering an efficient new approach for conductive hydrogel-based soft strain sensors.