Beyond Long-Term Protection by Intelligent Poly(lactic acid) Nanofibers: Structuring Multiscale Hierarchies for Passive Sensing

Conspectus

Recent advances in electrospun biodegradable polymer nanofibrous membranes (NFMs) are reshaping the design of functional materials from passive morphological optimization toward programmed charge regulation and function-oriented structural engineering. Extending this concept to biobased poly(lactic acid) (PLA), however, remains challenging because PLA exhibits weak cooperative alignment of ester dipoles, a low dielectric response, and a limited number of highly polar or ionizable groups. These molecular characteristics give rise to shallow charge traps, insufficient interfacial polarization, and rapid charge dissipation across crystalline–amorphous regions. Therefore, the key scientific issue is not only how to fabricate porous PLA membranes but also how to organize their molecular conformations, crystalline domains, filler interfaces, and fibrous networks into a multiscale charge-regulation system.

Electrospinning provides an effective route for addressing this issue because electric-field stretching, jet elongation, solvent evaporation, and phase separation can simultaneously regulate PLA chain orientation, crystalline morphology, fiber assembly, and pore architecture without altering the chemical structure of PLA chains. On this basis, research has progressed from single-parameter optimization toward multidimensional structural regulation. First, tuning electrospinning parameters, including voltage, collection distance, solution viscosity, and collector motion, promotes axial chain orientation and cooperative ester-dipole alignment. This oriented conformation enhances crystalline ordering, enriches crystalline–amorphous interfaces, and creates favorable charge-trapping domains, while more ordered fiber assembly narrows pore-size distributions and improves airflow continuity. Second, stereocomplexation between poly(l-lactide) and poly(d-lactide) introduces tightly packed stereocomplex crystallites through stereospecific interchain interactions. These ordered crystallites intensify dipolar polarization, deepen trap energy levels, and improve charge-storage stability, thereby mitigating the poor electret durability of pristine PLA. Third, nanoscale filler interfacial engineering with electroactive porous or dielectric fillers, such as metal–organic frameworks and titanium dioxide, introduces dielectric heterogeneity, defect-rich interfaces, unsaturated coordination sites, and high-surface-area contact domains. These features enrich multilevel charge-trapping sites, promote interfacial polarization, facilitate localized charge regeneration, and impart additional functions, including adsorption, antibacterial activity, humidity tolerance, and photothermal or optical regulation.

An increasingly systematic understanding of the processing–structure–electroactivity–function relationship is accelerating the transition of PLA NFMs from mechanistic studies to engineering applications. The coordinated regulation of fiber orientation, stereocomplex crystallization, and nanofiller-mediated heterointerfaces enables coupled charge generation, capture, trap-mediated storage, interfacial migration, and dynamic regeneration. These charge-regulation pathways allow PLA membranes to harvest and retain charges generated during particle filtration, electromechanical deformation, airflow-induced friction, and physiological motion, while suppressing charge decay under humid or dynamically changing conditions. In particulate matter filtration, they couple electrostatic adsorption with optimized porous architectures to achieve efficient particle capture and low airflow resistance. In electromechanical conversion, they enhance triboelectric and piezoelectric responses for biodegradable self-powered systems. In health monitoring, stable charge transduction improves physiological signal acquisition and sensing reliability.

In this Account, we critically summarize how electrospinning process regulation, stereocomplexation, and nanofiller interface engineering govern multiscale structures and electroactivity in PLA NFMs. We establish a processing–structure–electroactivity–function framework that involves fiber morphology, crystalline organization, interfacial polarization, charge trapping, and application performance across molecular, interfacial, and membrane scales. It essentially highlights hierarchical structuring as the key to designing intelligent biodegradable nanofibers for efficient filtration, self-powered sensing, wearable health monitoring, and adaptive protective systems.