MXene-Coated Hair Fibers as a Versatile Platform for Flexible Electronics, Intelligent Sensing, and Energy Harvesting

Abstract Hair fibers with α-keratin biopolymers are responsive to water owing to the reversible disruption and formation of hydrogen bonds, which can be constructed as a hygrometer. However, the functionality is insufficient in smart sensors and energy harvesting because of their intrinsic insulation. Herein, electrically conductive hair fibers are produced by the layer-by-layer assembly method through forming MXene sheaths. Bovine serum albumin (BSA) with a positive charge is assembled firstly onto the hair fibers, and MXene nanosheets are adsorbed on the surface of the hair through electrostatic interactions. Due to the superior electrical conductivity of MXene and water responsivity of hair, hair fibers can be used in electric devices with enhanced mechanical properties and humidity sensitivity. The resultant fibers can be used as smart strain sensors with a high response speed (600 ms). More importantly, electric energy with a maximum output voltage of 97 mV can be achieved under water evaporation based on the transpiration-driven electrokinetic effect. Thus, this study not only extends fundamental knowledge about electrically conductive fiber but also develops an intriguing method to develop multifunctional hair fibers applicable in degradable wearable sensors and energy harvesting.