Recyclable Ionic Conductive Hydrogels Based on Autonomous Polymerization of α-Lipoic Acid for Flexible Wearable Electronic Sensors

Ionic conductive hydrogels (ICHs) have attracted extensive attention in the field of flexible wearable electronic sensors as a result of softness, biocompatibility, self-healing ability, mechanical elasticity, and high-sensitivity conductivity. However, the existing preparation process of ICHs is mostly complicated, and the use of nonrenewable raw materials might be unfavorable for the recycling of ICHs. Therefore, taking into account extensibility, ion conductivity, self-healing, and adhesion, how to prepare ICHs with excellent recyclability by a simple and practicable method remains a great challenge. In this work, poly(α-lipoic acid) (PLA), Fe 3+, sodium alginate (SA), and 1-ethyl-3-methylimidazolium ethyl sulfate ([EMI][ES]) are used to achieve the above functions of ICHs. Because of the reversibility of dynamic interactions (including metal coordination bonds, ionic bonds, hydrogen bonds, and electrostatic interactions), the prepared ICHs have remarkable stretchability (2000%), self-healing property (96.37% efficiency), and adhesiveness. In addition, the conductivity sensitivity (GF) of the ICH can reach 1.31, and the response time can improve to 205 ms. As a flexible wearable electronic sensor, it can monitor and distinguish large-scale human movements and subtle physiological activities. Moreover, the ICH can be completely recovered and reused through simply dissolving with water and solvent evaporation without a significant loss of original functions. This ionic conductive hydrogel with synergistic functions is expected to provide a way for people to develop ideal green flexible wearable electronic sensors.