Tough, Repeatedly Adhesive, Cyclic Compression-Stable, and Conductive Dual-Network Hydrogel Sensors for Human Health Monitoring

Hydrogel-based flexible wearable devices have attracted wide attention from researchers due to their great potential application in human–computer interaction, electronic skin, and disease diagnosis. However, the preparation of conductive hydrogels integrating good biocompatibility, excellent mechanical (tensile and compressible) properties, self-adhesive properties, cyclic stretching, and compression stability remains a challenge. By the Schiff base reaction between dialdehyde carboxymethyl cellulose and amino gelatin to form the first layer of the network and by the free-radical polymerization of acrylic acid to form the second layer of the network, a multifunctional conductive dual-network (DN) hydrogel strain sensor was prepared. The composite DN hydrogel has excellent compression properties (the strength reached to 0.12 MPa when the hydrogel was compressed to 50% of its original height), good cyclic compression (≥10 000 times), repeatable adhesion (≥10 times), reliable electrical conductivity, and high sensitivity (gauge factor = 8.1). The biocompatible hydrogel can be used not only to monitor human body movement but also to detect the breathing movement of simulated pig lungs in vitro. Furthermore, the conductive hydrogel was creatively made into a plantar pressure sensor similar to an insole to monitor the stress on the sole of a flatfoot patient, providing a new potential material for flatfoot detection and correction.