Ultrafast Self-Healing, Reusable, and Conductive Polysaccharide-Based Hydrogels for Sensitive Ionic Sensors

The ever-growing demand for wearable electronic devices is stimulating the development of novel materials for fabrication of flexible electronics. Among all promising candidates, polysaccharide-based hydrogels are constructing a prospective pattern for achieving flexible electronic functionalities, benefiting from their ecofriendliness, renewability, biodegradability, and sustainability. However, one of the most important drawbacks of these hydrogels is slow self-healing. To address the abovementioned issue, we propose a simple method to fabricate a starch-based (starch/polyvinyl alcohol (PVA)/borax, SPB) conductive hydrogel. Due to the dual reversible interactions of hydrogen bonding and the boronic ester linkages, the hydrogel presents enhanced mechanical performance and ultrafast self-healing ability both in air and underwater. The mechanical properties recover within 10 s in air and within 120 s underwater, and the electronic functionality recovers within 90 ms in air and within 110 ms underwater. In addition, the abovementioned two interactions also endow the hydrogel with reversible sol-gel transition properties, which allow the hydrogel to be reused repeatedly. Due to large amounts of Na+ and free B(OH)4- ions, the hydrogel showed great conductivity and may work as strain sensor with high sensitivity (GF = 1.02 at 110-200% strains). The ionic hydrogel sensor could rapidly (≤180 ms) perceive human motions, even very small motions such as swallowing and pronunciation. With the combination of these seductive features, such an ecofriendly polysaccharide-derived hydrogel prepared through a facile and green preparation process would have great potential application for sustainable wearable sensors.