A tough conductive hydrogel with triple physical cross-linking, pH-Responsive swelling behaviors, and excellent strain sensitivity

Hydrogels as flexible strain sensors (FSSs) have attracted tremendous interest in the area of human movement monitoring. Such an application is developing rapidly. However, it is still valuable to explore hydrogel-based FSSs with excellent mechanical properties, responsiveness to stimulus, high strain sensitivity, and reliable sta-bility. Herein, a hydrogel with triple physical cross-linking (TPC hydrogel), whose structure also included hy-drophobic association-microcrystallinity-ionic coordination, was designed and fabricated. Synthetic water-soluble polymer [poly(vinyl alcohol) (PVA)] and natural polymer [sodium alginate (SA)] were introduced into the hydrogel; PVA induced microcrystal cross-linking, while SA provided ionic conductivity for the hydrogel. TPC hydrogels exhibited high toughness (5.9 MJ/m3) and excellent deformation (2490%). The introduction of SA also endowed the hydrogels with improved capability to ionize, imparting them with excellent pH-responsive swelling behavior. Impressively, TPC hydrogel-based FSSs exhibited reasonable conductivity (0.65-2.47 S/m), high sensitivity (maximum gauge factor = 10.29), and outstanding reliability and stability. This investigation broadens the avenue for the design and fabrication of hydrogels intended as FSSs with low modulus (33-45 kPa, close to human skin), excellent stretchability, and high strain sensitivity and durability.