Stretchable, tough, self-healing, antifreezing, and multifunctional nanocellulose-based hydrogel for wearable monitoring of human motion

Abstract

Hydrogels are among the most promising flexible sensing materials, exhibiting extensive applications in wearable devices, human health monitoring, robotics, etc. Currently, hydrogels that are stretchable, self-healing, antifreezing, and conductive have become the focus of research on wearable sensors. However, integrating high tensile strength, self-healing, frost resistance, and satisfactory mechanical properties into a conductive hydrogel remains challenging. Herein, soy hull nanocellulose, graphene oxide, and CaCl₂ were integrated into a polyvinyl alcohol–chitosan framework through green physical-crosslinking and ionic-crosslinking methods to build a porous three-dimensional network structure and develop a strong, tough, self-healing, antifreezing, and multifunctional hydrogel. This hydrogel benefits from abundant hydrogen, ester, and metal coordination bonds and electrostatic interactions, which contribute to its exceptional tensile strength (709.48 %), viscoelasticity (1081.71 kPa), mechanical strength (tensile strength = 4.91 MPa and compressive strength = 5.11 MPa), conductivity (5.11 S/m), and frost resistance (−35 ℃). Moreover, it exhibits high sensitivity with a measurement factor of 7.14 and maintains impressive electrical stability after 800 cycles of stretching at room temperature (25 ℃) and a low temperature (−35 ℃). Further, this hydrogel is used for applications such as human limb bending and heart rate monitoring. Overall, this research offers a promising approach for developing sustainable and multifunctional hydrogels as well as provides notable insights with regard to flexible wearable sensors.