Highly\nStretchable and Biocompatible Strain Sensors\nBased on Mussel-Inspired Super-Adhesive Self-Healing Hydrogels for\nHuman Motion Monitoring

Abstract

Integrating\nmultifunctionality such as adhesiveness, stretchability,\nand self-healing ability on a single hydrogel has been a challenge\nand is a highly desired development for various applications including\nelectronic skin, wound dressings, and wearable devices. In this study,\na novel hydrogel was synthesized by incorporating polydopamine-coated\ntalc (PDA–talc) nanoflakes into a polyacrylamide (PAM) hydrogel\ninspired by the natural mussel adhesive mechanism. Dopamine molecules\nwere intercalated into talc and oxidized, which enhanced the dispersion\nof talc and preserved catechol groups in the hydrogel. The resulting\ndopamine–talc–PAM (DTPAM) hydrogel showed a remarkable\nstretchability, with over 1000% extension and a recovery rate over\n99%. It also displayed strong adhesiveness to various substrates,\nincluding human skin, and the adhesion strength surpassed that of\ncommercial double-sided tape and glue sticks, even as the hydrogel\ndehydrated over time. Moreover, the DTPAM hydrogel could rapidly self-heal\nand regain its mechanical properties without needing any external\nstimuli. It showed excellent biocompatibility and improved cell affinity\nto human fibroblasts compared to the PAM hydrogel. When used as a\nstrain sensor, the DTPAM hydrogel showed high sensitivity, with a\ngauge factor of 0.693 at 1000% strain, and was capable of monitoring\nvarious human motions such as the bending of a finger, knee, or elbow\nand taking a deep breath. Therefore, this hydrogel displays favorable\nattributes and is highly suitable for use in human-friendly biological\ndevices.