A triple-network PVA/cellulose nanofiber composite hydrogel with excellent strength, transparency, conductivity, and antibacterial properties

Polyvinyl alcohol (PVA)-based hydrogels are widely used in the fields of tissue engineering, biomedicine, and flexible sensors due to their low cost, excellent biocompatibility, and simple gelation methods. Repeated freeze-thaw cycles are essential for the preparation of such hydrogels. Although this process can enhance the mechanical properties of the hydrogels to a certain extent, it can also result in opacity and limited tensile performance, significantly restricting their application in wearable devices and electronic skin. This study introduced cellulose nanofibers into polyacrylamide (PAM)/PVA double interpenetrating network hydrogel system, achieving the preparation of a multifunctional composite hydrogel with a “triple-network interlock” structure. Under the synergistic effects of multiple networks, multiple hydrogen bonds, and nano-reinforcement, this composite hydrogel requires only a single freeze-thaw cycle to achieve a tensile strength exceeding 1 MPa, which is significantly higher than that of PVA hydrogels subjected to multiple freeze-thaw cycles. The PVA-based hydrogel prepared in this work balances tensile strength (1.41 MPa), elongation (1332%), transparency (89.8%), and toughness (6.73 MJ m⁻³). Additionally, this composite hydrogel exhibits high sensitivity (GF = 8.74), rapid response (108 ms), fatigue resistance, and antibacterial properties, making it a reliable strain sensor over a wide strain range. When encapsulated on human joints, it can monitor body movements in real-time, such as movements of fingers, wrists, elbows, and knees, and can be integrated into peripheral circuits to achieve precise real-time control of robotic hands. This work presents a multifunctional composite hydrogel with great potential as a candidate material for tissue engineering, human-machine interaction, and high-performance wearable sensors.