Mussel-Inspired Cellulose Nanocomposite Tough Hydrogels\nwith Synergistic Self-Healing, Adhesive, and Strain-Sensitive Properties

Abstract

The remarkable progress\nin efforts to prepare conductive self-healing\nhydrogels mimicking human skin’s functions has been witnessed\nin recent years. However, it remains a great challenge to develop\nan integrated conductive gel combining excellent self-healing and\nmechanical properties, which is derived from their inherent compromise\nbetween the dynamic cross-links for healing and steady cross-links\nfor mechanical strength. In this work, we design a tough, self-healing,\nand self-adhesive ionic gel by constructing synergistic multiple coordination\nbonds among tannic acid-coated cellulose nanocrystals (TA@CNCs), poly­(acrylic\nacid) chains, and metal ions in a covalent polymer network. The incorporated\nTA@CNC acts as a dynamic connected bridge in the hierarchically porous\nnetwork mediated by multiple coordination bonds, endowing the ionic\ngels the superior mechanical performance. Reversible nature of dynamic\ncoordination interactions leads to excellent recovery property as\nwell as reliable mechanical and electrical self-healing property without\nany assistance of external stimuli. Intriguingly, the ionic gels display\ndurable and repeatable adhesiveness ascribed to the presence of catechol\ngroups from the incorporated tannic acid, which can be adhered directly\non human skin without inflammatory response and residual. Additionally,\nthe ionic gels with a great strain sensitivity can be employed as\nflexible strain sensors to monitor and distinguish both large motions\n(e.g., joints bending) and subtle motions (e.g., pulse and breath),\nwhich enable us to analyze the data on the user interface of smart\nphone via programmable wireless transmission. This work provides a\nnew prospect for the design of the biocompatible cellulose-based hydrogels\nwith stretchable, self-adhesive, self-healing, and strain-sensitive\nproperties for potential applications in wearable electronic sensors\nand healthcare monitoring.