Bio-inspired gradient poly(lactic acid) nanofibers for active capturing of PM0.3 and real-time respiratory monitoring

The concept of bio-inspired gradient hierarchies, in which the well-defined MOF nanocrystals serve as active nanodielectrics to create electroactive shell at poly(lactic acid) (PLA) nanofibers, is introduced to promote the surface activity and electroactivity of PLA nanofibrous membranes (NFMs). The strategy enabled significant refinement of PLA nanofibers during coaxial electrospinning (~40% decline of fiber diameter), accompanied by remarkable increase of specific surface area (nearly 1.5 m2/g), porosity (approximately 85%) and dielectric constants for the bio-inspired gradient PLA (BG-PLA) NFMs. It largely boosted initial electret properties and electrostatic adsorption capability of BG-PLA NFMs, as well as charge regeneration by TENG mechanisms even under high-humidity environment. The BG-PLA NFMs thus featured exceptionally high PM0.3 filtration efficiencies with well-controlled air resistance (94.3%, 163.4Pa, 85L/min), in contrast to the relatively low efficiency of only 80.0% for normal PLA. During the application evaluation of outdoor air purification, excellent long-term filtering performance was demonstrated for the BG-PLA for up to 4hours (nearly 98%, 53Pa), whereas normal PLA exhibited a gradually declined filtration efficiency and an increased pressure drop. Moreover, the BG-PLA NFMs of increased electroactivity were ready to generate tribo-output currents as driven by respiratory vibrations, which enabled real-time monitoring of electrophysiological signals. This bio-inspired gradient strategy opens up promising pathways to engender biodegradable nanofibers of high surface activity and electroactivity, which has significant implications for intelligent protective membranes. Environmental Implication As a timely topic in the field of air filtration research, electrospinning of biodegradable poly(lactic acid) (PLA) membranes signifies a versatile and sustainable approach towards fabrication of multifunctional filters. Unfortunately, the electrospun PLA micro/nanofibers are normally characterized by low electroactivity and surface activity and poor electret capability, limiting the active capture of fine or ultrafine airborne particulate matters (PMs). We unravel a bio-inspired strategy to engender hierarchically gradient PLA nanofibers with increased surface activity and electroactivity while providing desirable air permeability, in great need for long-term PM0.3 filtration and intelligent wireless monitoring.