A self-adhesive wearable strain sensor based on a highly stretchable, tough, self-healing and ultra-sensitive ionic hydrogel

Abstract

Flexible and conductive hydrogel sensors have great potential for applications in wearable and implantable devices, electronic skin and healthcare diagnosis. However, it remains a great challenge to develop an integrated tough hydrogel sensor combining stretchability, adhesiveness, self-healing ability and high sensitivity via a simple, fast and economical approach for multi-field applications. In this work, we designed a multifunctional composite self-adhesive conductive hydrogel by using chitosan (CS), tannic acid (TA) and polyacrylic acid (PAA), and ionic cross-linker Al³⁺. The synergistic multiple and reversible coordination bonds and hydrogen bonds in the matrix lead to a combination of high stretchability, rapid self-recovery, great anti-fatigue and rapid self-healing properties of the tough hydrogel. Additionally, the ionic gels displayed durable and repeatable adhesiveness ascribed to the presence of catechol groups from TA, which can adhere directly on human skin without residuals and inflammatory responses. Furthermore, our ionic hydrogel sensors exhibited a broad strain window (0–1400%) and demonstrated brilliant stretching sensitivity (gauge factor as high as 12.2), and it displayed stable sensing performance for repeated real-time monitoring of both large and subtle deformation (e.g. knee joint motions, breathing modes, and even the slight pulse changes in different motion states). This work provides a feasible method to construct self-adhesive and self-healing hydrogel sensors with high sensitivity and a large-range detection capacity and paves a way for versatile applications in electronic skin, healthcare monitoring and medical electrodes.