Processable, Ion-Conducting Hydrogel for Flexible Electronic Devices with Self-Healing Capability

Abstract

Conductive, self-healing, and adhesive hydrogels are of great significance in wearable electronic devices. The most important properties of conductive self-healing hydrogels are the efficient recovery of both electrical and mechanical properties at room temperature and prolonged durability. In this work, we developed a novel double-network hydrogel consisting of poly(4-styrene sulfonate-co-methyl-uracil-imidazolium) chloride (PSS-MUI), gelatin, and ferric ions (Fe³⁺). Here, the MUI serves as a supramolecular crosslinker, while ferric ions act as ionic crosslinkers between gelatin and PSS functional groups. The hydrogel demonstrated excellent stretchability and outstanding ionic conductivity. The reversible nature of dynamic hydrogen bonding and ionic and metal coordination interactions rendered the hydrogel self-healing ability, strong adhesion, and rapid electrical performance recovery. Variation in the Fe³⁺ concentration proved to influence the time window of hydrogel processability and allowed tuning the hydrogel mechanical and ion-conducting properties. The optimal Fe³⁺ ion concentration for use in a processable, ion-conducting hydrogel was found to be 2 wt %. During repeated stretching, the hydrogel showed only small changes in its electrical resistance. An electric circuit was successfully assembled onto a flexible polyurethane (PU) substrate where the power supply, light-emitting diode, and resistor were connected with the hydrogel, serving as a conductive wire. Upon breakage of the wire, simple extrusion of the hydrogel precursor into the gap yielded instant repair of the circuit. Thus, the hydrogel demonstrated suitability for use in flexible electronic devices.