Highly Tough, Freeze-Resistant, Sensitive, and Recyclable Starch-based Multifunctional Hydrogel Flexible Wearable Sensor for Human Motion Monitoring

Abstract

Conductive hydrogel strain sensors have attracted great attention in various fields. However, most conductive hydrogels are rigid due to the polymerization of conductive polymers, which not only affects wearer comfort but also causes environmental concerns due to their non-biodegradable nature. To address these limitations, researchers have begun incorporating natural polymer compounds into hydrogels, including starch-based hydrogels. However, starch-based hydrogels hinder their applications due to their brittle fracture, poor freezing resistance, and insufficient electrical conductivity. Herein, a multi-functional, environmentally friendly, degradable starch-based conductive hydrogel was developed using a binary system of water and ethylene glycol (EG) as the solvents, starch and polyvinyl alcohol (PVA) as the skeletons, calcium chloride (CaCl₂) for conductivity, and gelatin and cellulose nanofibers to synergistically modify the physical cross-linked network. The hydrogel exhibited exceptional properties such as excellent stretchability (478.1%), high tensile strength (2.1 MPa), good toughness (3.7 MJ/m³), and good conductivity (0.22 S/m), as well as excellent anti-freezing and recyclability. Leveraging these properties, a wearable strain and temperature sensor with high sensitivity (GF = 0.74) and cycle stability over a wide strain range was developed, enabling convenient monitoring of human movement and body temperature physiological signals.