Emerging cellulose-derived materials: a promising platform for the design of flexible wearable sensors toward health and environment monitoring

The ongoing surge in demand for high-performance wearable sensors for precisely monitoring vital signs of the human body or the surrounding environment has inspired the relentless pursuit of biocompatible and biodegradable advanced materials. Cellulose, as a class of well-known natural biopolymer on the Earth, presents distinctive integrated merits of good biocompatibility and biodegradability, easy processability into diverse material formats, and sustainable production on a large scale, as well as intrinsic shape anisotropy, surface charge/chemistry, and superior physical and mechanical properties. Such unique advantages have driven constant innovations in wearable and smart cellulose-containing sensors in the past few years. With the rapid development of fabrication techniques in material processing and progress in research, cellulose has been engineered into multidimensional architectures including 1D (nanofibers, fibers, and yarns), 2D (paper, films, and fabrics), and 3D (hydrogels, aerogels, foams, and sponges), which are further transformed into electrically conductive carbonaceous materials with tailorable structures and properties. Cellulose-derived materials have been developed as flexible biosupports or biosubstrates, sensing layers, electrodes and active components for wearable sensors by virtue of their favorable and unique material merits. In this review, the recent advances in the development of multidimensional and multifunctional cellulose-derived materials are discussed for wearable sensors toward healthcare and environment monitoring. First of all, the unique hierarchical and chemical structures and properties of cellulose are briefly introduced. Then, we summarize the fabrication strategies for processing cellulose into materials with multidimensional architectures. Additionally, the design and functionality of flexible wearable sensors developed with multidimensional cellulose-derived materials as biosubstrates, electrodes, active layers, and sensing components are presented in detail. In particular, cellulose-based advanced materials for self-powered sensors are also highlighted. Finally, some prospects on the future challenges in this emerging research field of designing cellulose-derived materials for wearable sensors are illustrated. This review may provide insightful inspiration for the design and utilization of cellulosic composites in flexible electronic devices with high-performance.