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.