Facile preparation of PHEMA hydrogel induced via Tannic Acid-Ferric ions for wearable strain sensing

As an important component of flexible electronic devices, strain sensing hydrogels have attracted extensive attention in the field of wearable sensors. However, the hydrogel matrix has some problems such as weak mechanical strength, lack of adhesion and poor performance stability. Herein, an ionic conductive poly (hydroxyethyl methacrylate) (PHEMA) hydrogel with good toughness and adhesion strength was prepared which was initiated by dynamic REDOX reaction of phenolic hydroxyl group and metal ions. The resulting PHEMA/ tannic acid (TA)-Fe hydrogel exhibits high flexibility (2227% elongation at break) and excellent adhesion properties (238 kPa on pig skin) due to the presence of TA and Fe 3+ ion. Rheological results demonstrated self-healing performance of the hydrogels, and cyclic compression experiments displayed the hydrogels exhibit very good fatigue resistance. Furthermore, the hydrogel showed well strain sensing ability under different stretch and compress conditions and could maintain the stability performance for at least 100 cycles within 100% strain. Therefore, the PHEMA/TA-Fe hydrogels prepared with a simple and convenient redox catalytic polymerization method possess great potential to be used in flexible electronic devices. • PHEMA/TA-Fe hydrogel was prepared inducing with a facile redox reaction of TA-Fe • PHEMA hydrogel was crosslinked with dynamic hydrogen bonds and metal coordination • PHEMA hydrogel showed high flexibility, excellent adhesion and self-healing abilities • PHEMA hydrogel exhibits well strain sensing ability under vary stretch or compress