Recent Progress in Cellulose-Based Flexible Sensors

Flexible sensors are attractive due to potential applications in body exercise and ambient gas monitoring systems. Cellulose and its derivatives have combined superiorities such as intrinsic and structural flexibility, ease of chemical functionalization, moisture sensitivity, and mechanical stability, enabling them to be promising candidates as flexible supporting substrates and flexible sensitive materials. Significant progress consequently has been achieved to improve mechanical, electrical, and chemical performance. The latest advance in materials synthesis, structure design, fabrication control, and working mechanism of novel cellulose-based flexible sensors are reviewed and discussed, including strain sensors, humidity sensors, and harmful gas sensors. Various strategies were summarized to enhance sensor performance by surface group modifications, inorganic and organic conducting fillers optimization, multilayer structure design. Newly emerged processing techniques of self-assembly, vacuum filtration, and 3D printing were introduced as well to construct multiscale microstructures. The integration of multiple sensors toward smart and healthy exercise monitoring system is briefly reviewed. The facing challenges and future opportunities of cellulose-based flexible sensors were discussed and proposed at the end. This review provides inspiration and guidelines on how to design and fabricate cellulose-based flexible sensors.