Enabling a Paper-Based Flexible Sensor to Work under Water with Exceptional Long-Term Durability through Biomimetic Reassembling of Nanomaterials from Natural Wood

Paper-based sensors have many distinguishingadvantages; however,how to improve their working durability especially under water isa critical issue in many applications and unfortunately remains ahuge challenge. In this work, we design and develop an innovativestrategy enabling paper-based strain and pressure sensors to workunder water with exceptional long-term working durability by biomimeticreassembling of nanomaterials from natural wood. A composite paperconsisting of softwood fibers and 22 wt % graphite nanoplates wasprepared based on a papermaking protocol. Cellulose nanofibers wereadded to strengthen the composite paper, and lignin nanoparticleswere applied onto the paper surface via the papercoating technology to obtain its superhydrophobicity. Subsequently,the as-obtained superhydrophobic composite paper was assembled intoa flexible sensor that can be used to detect strain and pressure changesboth in air and under water. As the strain sensor, its gauge factorwas 10.9 and 14.6 in air and under water, and the corresponding responsetime was 0.3 and 0.15 s, respectively. Surprisingly, an exceptionalworking stability was achieved even after more than 10,000 bending-unbendingcycles under water. As the pressure sensor, its sensitivity (S) was 0.02 and 0.38 kPa(-1) in air andunder water, and the corresponding response time was 0.46 and 0.3s, respectively. Its long-term durability can also exceed 10,000 pressing-releasingcycles. This novel strategy developed in this work can be an effectiveapproach for biomimetic re-engineering of biomass-derived nanomaterials,aiming to develop highly stable paper-based flexible sensors thatcan find applications in wearable systems and underwater equipment. A degradable paper-based flexible sensoris prepared byreassembling the cellulose nanofibers and lignin nanoparticles fromnatural woods that can work under water.