Polyelectrolyte-derived adhesive, super-stretchable hydrogel for a stable, wireless wearable sensor

Abstract

The simultaneous integration of diverse performance attributes, such as self-adhesive capability, stretchability, mechanical stability, and high ionic conductivity, is one of the key issues in the research of wearable electronic devices. Moreover, a facile preparation method, as well as time efficiency and no heating requirement, is desirable for the use of hydrogels in widespread applications. In this study, a multi-functional hydrogel P(AMPSs-co-AAm)/SC was prepared by the rapid photo-polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPSs) and acrylamide (AAm) in the presence of sodium caseinate (SC). P(AMPSs-co-AAm)/SC exhibited tight contact and reversible adhesion on various substrates, including glass, steel, plastic, and even human skin. According to the dynamic interaction system of P(AMPSs-co-AAm) and SC, the hydrogel exhibited outstanding stretchability (reaching a fracture strain of 2929% and a stress of 128 kPa), as well as excellent fatigue resistance and network toughening even after multiple stretching/recovery cycles. In addition, a polymeric ionic charge carrier, such as AMPSs, not only endowed a high ionic conductivity (up to 1.2 S m⁻¹) to the hydrogel, but also structural stability, leading to the excellent electric stability of the hydrogel throughout repeated mechanical strain cycles. Our developed approach demonstrates the potential for application as long-life wearable strain sensors for detecting human body motion.