Bioelectrets in Electrospun Bimodal Poly(lactic acid) Fibers: Realization of Multiple Mechanisms for Efficient and Long-Term Filtration of Fine PMs

Self-crystal electret poly(lactic acid) nanofibers for high-flow air purification and AI-assisted respiratory diagnosis

Particulate matters (PMs), one of the major airborne pollutants, continue to seriously threaten human health and the environment. Here, a self-crystal-induced electret enhancement (SCIEE) strategy was developed to promote the in-situ electret effect and polarization properties of electrospun poly(L-lactic acid) (PLLA) nanofibers. The strategy specifically involved the elaborate pre-structuring of stereocomplex crystals (SCs) with uniform dimensions (∼300 nm), which were introduced into PLLA electrospinning solution as the electrets and physical cross-linking points of high density. It enabled direct fabrication of self-crystal electret poly(lactic acid) (SCE-PLA) nanofibrous membranes (NFMs), effective regulation of nanofiber morphology, enhanced generation of electroactive phases (β phases, SCs, and interfacial domains), synergistically contributing to remarkable increase of dielectric constant (2.48), surface potential (4.60 kV) and charge regeneration performance (tribo-output voltage as high as 37.60 V). This permitted multiple improvements in physical interception and electrostatic adsorption of PMs, as exemplified by efficient removal of PM0.3 and PM2.5 (94.91 % and 99.15 %) with ultralow air resistance (57.2 Pa, 32 L/min), in clear contrast to the pure PLA counterpart (82.66 % and 80.98 %). Given sustainable regeneration of plentiful charges, SCE-PLA NFMs exhibited long-term electret effect and PM0.3 removal (92.53 %) even at intensive inhalation and exhalation airflow (120 and 100 L/min). Moreover, the electroactive SCE-PLA NFMs were ready to realize high-accuracy monitoring (99.23 %) of the respiratory patterns. Our SCIEE strategy opens up a promising pathway to fabricate ecofriendly nanofibers featuring superior in-situ electret effect and charge regeneration capability, appealing for air purification and passive monitoring.

Lotus leaf-inspired poly(lactic acid) nanofibrous membranes with enhanced humidity resistance for superefficient PM filtration and high-sensitivity passive monitoring

The biomimetic design principles offer promising solutions to fabrication of multifunctional nanofibrous membranes (NFMs) with on-demand hierarchies and properties. Herein, a combined electrospinningelectrospray approach was employed to firmly anchor MOF nanocrystals onto poly(lactic acid) (PLA) nanofibers, resembling the naturally occurring dense protrusions at the lotus leaf. The formation of unique MOF-protruding superstructures gave rise to an exceptional combination of increased electroactivity, in-situ electret properties and charge regeneration mechanisms, as well as remarkable humidity resistance. With 8 wt% bioinspired MOF-protrusions for the electrospunelectrosprayed PLA NFMs (BM-PLA8), the initial surface potential was elevated to 3.0 kV and slightly decreased to 2.6 kV after 7-day ageing, in clear contrast to only 1.1 and 0.6 kV for the normal PLA, respectively. Moreover, the tribo-output voltage and current were significantly promoted for BM-PLA8 (64.5 V and 151.6 nA), demonstrating high humidity resistance and long-term robustness even at 90 % RH. It conferred distinct improvements in air filtration performance for BM-PLA8 even at the highest airflow velocity of 85 L/min (below 250 Pa, 99.9 % and 95.0 % removal of PM2.5 and PM0.3, respectively), far surpassing the normal PLA counterpart (nearly 350 Pa, 89.5 % and 75.8 %). Arising from the respiration-driven charge regeneration mechanisms, passive respiratory monitoring of high sensitivity was demonstrated for BM-PLA8, showing great promise for efficient healthcare under the challenging circumstances.

High-efficiency respiratory protection and intelligent monitoring by nanopatterning of electroactive poly(lactic acid) nanofibers

The advent of multifunctional nanofibrous membranes (NFMs) has led to the development of next-generation air filters that are ready to intercept fine particulate matters (PMs) and monitor the respiratory diseases. However, it is still challenging to fabricate biodegradable NFMs featuring the desirable combination of high filtration efficiencies, low air resistance, and intelligent real-time monitoring. Herein, a hierarchical nanopatterning approach was proposed to functionalize the stereocomplexed poly(lactic acid) (PLA) (SC-PLA) nanofibers via the combined electrospinning of SC-PLA and electrospray of CNT@ZIF-8 nanohybrids. The nanopatterned SC-PLA (NSC-PLA) NFMs were characterized by largely increased surface activity and electroactivity, as evidenced by the nearly two-fold increase in surface potential (up to 7.3 kV) and substantial improvements in the dielectric properties. Furthermore, the NSC-PLA NFMs exhibited excellent tribo-output performance, yielding a voltage of as high as 13.5 V for NSC-PLA NFMs loaded 10 % nanohybrids (NSC-PLA10). In particular, the exceptionally high electroactivity and unique protrusion structure together contributed to promote the filtration efficiencies, while providing a low pressure drop (e.g., 96.1 % for PM2.5 and 88.3 % for PM0.3, only 67.6 Pa of NSC-PLA10, at 32 L/min). More importantly, NSC-PLA NFMs enabled real-time monitoring of physiological signals during different respiratory states, as evidenced by the output voltages of 17.2, 32.9 and 37.5 mV for normal breath, fast breath and cough recorded by NSC-PLA10. The proposed NSC-PLA NFMs show enormous potential in the fields of air filtration and real-time respiratory monitoring, thus providing ecofriendly solutions to personal health management.

Ultralow-resistance and self-sterilization biodegradable nanofibrous membranes for efficient PM0.3 removal and machine learning-assisted health management

The development of multifunctional nanofibrous membranes (NFMs) that enable anti-viral protection during air purification and respiratory disease diagnosis for health management is of increasing importance. Herein, we unraveled a heterostructure-enhanced electro-induced stereocomplexation (HEIS) strategy to fabrication of poly(lactic acid) (PLA) NFMs enabling a combination of efficient PM removal, respiratory monitoring and self-sterilization. The strategy involved an electro-induced stereocomplexation (EIS) approach to trigger the generation of hydrogen bonds between enantiomeric poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) chains, promoting CO dipole alignment and molecular polarization during electrospinning. This was further enhanced by incorporation of Ag-doped TiO2 (Ag-TIO) nanodielectrics to promote the electroactivity and surface activity, conferring profound refinement of PLA nanofibers (from 460 nm to an ultralow level of 168 nm) and high porosities of over 91 %. Arising from the sustainable generation of plentiful charges based on triboelectric nanogenerator (TENG) mechanisms, the electroactive PLA NFMs exhibited remarkable triboelectric properties even in high-humidity environments (80 %RH), excellent PM0.3 filtration efficiency with an ultralow pressure drop (93.1 %, 31.8 Pa, 32 L/min), and 100 % antimicrobial efficiency against both E. coli and S. aureus. Moreover, a deep-learning algorithm based on convolutional neural network (CNN) was proposed to recognize various respiratory patterns. The proposed strategy confers the biodegradable NFMs an unusual combination of ultralow-resistance air purification and machine learning-assisted health management, signifying promising prospects in environmental protection and personal healthcare.

Application of Biomass-Based Triboelectrification for Particulate Matter Removal

Electrostatic fields are crucial for achieving the highly efficient filtration of airborne pollutants. However, the dissipation of static charges over time, especially under humid conditions, limits their practical application. In this study, we present a self-charging air filter (SAF) powered by a triboelectric nanogenerator (TENG). This SAF is integrated into a commercial mask, termed SAFM, which can effectively capture and degrade airborne pollutants without requiring an external power source. By leveraging the triboelectric effect during breathing, the TENG within the SAFM continuously replenishes static charges, maintaining the triboelectric field. The system employs a cellulose aerogel/Ti3C2Tx composite as the electron donor and an esterified cellulose-based electrospun nanofiber as the electron acceptor. Remarkably, the triboelectric field significantly enhances filtration performance, with the SAF achieving up to 95.7% filtration efficiency for particulate matter as small as 0.3 μm. This work underscores the potential of TENG-powered triboelectric fields in the development of multifunctional, human-machine interactive facemasks.

MOF Nanosheet-Functionalized Poly(lactic acid) Meta-membranes for Long-Term Air Purification and Intelligent Monitoring

The wide use of conventional polymeric air filters is causing a dramatically increasing accumulation of plastic and microplastic pollution. The development of poly(lactic acid) (PLA) fibrous membranes for efficient air purification is of important significance but frequently challenged by the rapid decay of filtration performance due to the intrinsically poor electret properties of PLA. Here, we propose an electroactivity promotion methodology, involving the one-step synthesis and homogeneous incorporation of high-dielectric ZIF-8 nanosheets (ZIFNSs), to facilitate interfacial polarization and fiber refinement during electrospinning of PLA nanofibers. The preparative electrospun PLA/ZIFNS meta-membranes exhibited an unusual combination of significantly reduced nanofiber diameter (∼462 nm), enhanced surface potential (approaching 10 kV), and increased surface activity and facilitated the formation of electroactive phases. With well-controlled morphological features, the highly electroactive PLA/ZIFNS meta-membranes exhibited exceptional filtration efficiencies for PM2.5 and PM0.3 (99.2 and 96.0%, respectively) even at the highest airflow rate of 85 L/min, in clear contrast to that of its pure PLA counterpart (only 79.3 and 74.6%). Arising from the increased electroactivity and active contact sites, remarkable triboelectric performance and self-charging mechanisms were demonstrated for the PLA/ZIFNS meta-membranes, contributing to long-term efficient PM0.3 filtration (97.5% for over 360 min). Moreover, as triggered by physiological activities like respiration and speaking, the electroactive PLA/ZIFNS meta-membranes enabled real-time monitoring with high sensitivity and specificity. The proposed strategy affords significant promotion of electroactivity and triboelectric performance for PLA nanofibers, which may motivate the development of ecofriendly protective membranes for respiratory healthcare and real-time monitoring.

Interfacial Polarization Strategy to Electroactive Poly(lactic acid) Nanofibers for Humidity-Resistant Respiratory Protection and Machine Learning-Assisted Monitoring

The advancement of intelligent and biodegradable respiratory protection equipment is pivotal in the realm of human health engineering. Despite significant progress, achieving a balance between efficient filtration and intelligent monitoring remains a great challenge, especially under conditions of high relative humidity (RH) and high airflow rate (AR). Herein, we proposed an interfacial stereocomplexation (ISC) strategy to facilitate intensive interfacial polarization for poly(lactic acid) (PLA) nanofibrous membranes, which were customized for machine learning-assisted respiratory diagnosis. Theoretical principles underlying the facilitated formation of the electroactive phase and aligned PLA chains were quantitatively depicted in the ISC-PLA nanofibers, contributing to the increased dielectric constant and surface potential (as high as 2.2 and 5.1 kV, respectively). Benefiting from the respiration-driven triboelectric mechanisms, the ISC-PLA demonstrated a high PM0.3 filtration efficiency of over 99% with an ultralow pressure drop (75 Pa), even in challenging circumstances (95 ± 5% RH, AR of 85 L/min). Furthermore, we implemented the ISC-PLA with multifunction respiratory monitoring (response time of 0.56 s and recovery time of 0.25 s) and wireless transmission technology, yielding a high recognition rate of 83% for personal breath states. This innovation has practical implications for health management and theoretical advancements in respiratory protection equipment.

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 %, 163.4 Pa, 85 L/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 4 h (nearly 98.0 %, 53 Pa), 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.

Preparation of ethyl cellulose bimodal nanofibrous membrane by green electrospinning based on molecular weight regulation for high-performance air filtration

Preparing bio-based air filtration membrane through green electrospinning strategy is a vital approach to alleviating environmental and energy crises. However, the development of related biomaterials and method for regulating membrane structure are still lacking. In this study, ethyl cellulose (EC) bimodal nanofibrous membrane was prepared by electrospinning using ethanol and water as solvents to achieve high-performance air filtration. A new strategy for bimodal fiber molding based on molecular weight modulation was proposed. The EC polymer chains with medium molecular weights were subject to the highest degree of inhomogeneity of solvent intrusion, and there were significant differences in viscous forces "microscopically", leading to the formation of bimodal structure by inhomogeneous stretching of the jet. The well-defined bimodal structure endowed EC membrane with excellent air filtration performance. The filtration efficiency for PM0.3, pressure drop, quality factor were 99.11 %, 42.2 Pa, and 0.112 Pa-1, respectively. Compared to the commonly used zein, EC cost just 12.77 %, and its solution had a 50 % longer shelf life, making it a more desirable biomaterial. This work will facilitate the application of more biomaterials in air filtration, promote the green fabrication of high-performance air filtration membranes, and realize sustainable development.

Tribo-charge enhanced and cellulose based biodegradable nanofibrous membranes with highly fluffy structure for air filtration and self-powered respiration monitoring systems

Recently, the demand for healthcare products especially wearable smart masks is increasing. The biosafety and degradability of smart masks are crucial for human health and environmental protection. However, the development of biodegradable and biocompatible fibrous membranes with high filtration efficiency and low pressure drop is still a challenge. How to realize the collaborative improvement between air filtration efficiency and pressure drop of the nanofibrous membrane is still a challenge. Here, a tribo-charge enhanced and biodegradable nanofibrous membranes (TCB NFMs) with highly fluffy structure for air filtration and self-powered respiration monitoring systems is reported for the first time. The filtration efficiency and pressure drop of the prepared membranes for 0.3 µm NaCl particulates is 99.971% and 41.67 Pa. The TCB NFMs based smart mask possesses a series of satisfactory and excellent characteristics, such as self-powered, biodegradable, biocompatible, high filtration efficiency, and low pressure drop, which is highly promising for application in air filtration systems and intelligent wearable respiration monitoring systems.

Nanopatterning of beaded poly(lactic acid) nanofibers for highly electroactive, breathable, UV-shielding and antibacterial protective membranes

Despite great potential in fabrication of biodegradable protective membranes by electrospinning of poly(lactic acid) (PLA) nanofibers, it is still thwarted by smooth surfaces and poor electroactivity that challenge the promotion of electret properties and long-term air filtration performance. Here, a microwave-assisted synthetic method was used to customize dielectric TiO2 nanocrystals of ultrasmall and uniform dimensions (∼30 nm), which were homogeneously embedded at beaded PLA nanofibers (PLA@TiO2, diameter of around 280 nm) by the combined "electrospinning-electrospray" approach. With small amounts of TiO2 (2, 4 and 6 wt%), the nanopatterned PLA@TiO2 nanofibrous membranes (NFMs) were characterized by largely increased dielectric constants (nearly 1.9), surface potential (up to 1.63 kV) and triboelectric properties (output voltage of 12.2 V). Arising from the improved electroactivity and self-charging mechanisms, the nanopatterned PLA@TiO2 NFMs exhibited remarkable PM0.3 filtration properties (97.9 %, 254.6 Pa) even at the highest airflow rate of 85 L/min, surpassing those of pure PLA membranes (86.2 %, 483.7 Pa). This was moreover accompanied by inhibition rates of 100 % against both E. coli and S. aureus, as well as excellent UV-blocking properties (UPF as high as 3.8, TUVA of 50.9 % and TUVB of 20.1 %). The breathable and electroactive nanopatterned PLA NFMs permit promising applications in multifunctional protective membranes toward excellent UV shielding and high-efficiency removal of both PMs and pathogens.

A ZIF-8-encapsulated interpenetrated hydrogel/nanofiber composite patch for chronic wound treatment

Designing wound dressings necessitates the crucial considerations of maintaining a moist environment and implementing effective bacterial control. Furthermore, developing a three-dimensional framework emulating the extracellular matrix (ECM) confers advantages in fostering cellular migration and proliferation. Inspired by this, hydrogel/nanofiber composites have been demonstrated as promising materials for wound dressings. The composites also overcome the disadvantages of poor mechanical properties and rapid release of traditional pure hydrogels. In this study, we constructed a calcium alginate hydrogel/polylactic acid nanofiber (CAH/PLANF) composite with an interpenetrated network. Additionally, the synthesis of zeolitic imidazolate framework-8 (ZIF-8) incorporated into the composite system endowed the system with enhanced mechanical properties and photodynamic antibacterial attributes. The obtained composite patch (ZIF-8@CAH/PLANF) exhibited excellent swelling, strong mechanical properties, low cytotoxicity, and durable photodynamic antibacterial effect with an antibacterial efficacy of higher than 99.99%. Finally, bacterial infection and wound healing properties were investigated in vivo, and the ZIF-8@CAH/PLANF patch was proven to have the ability to fight infection and accelerate wound healing.

Ethyl cellulose/gelatin/β-cyclodextrin/curcumin nanofibrous membrane with antibacterial and formaldehyde adsorbable capabilities for lightweight and high-performance air filtration

Functionalization of bio-based nanofibers is the development tendency of high-performance air filter. However, the conventional structural optimization strategy based on high solution conductivity greatly hinders the development of fully bio-based air filter, and not conducive to sustainable development. This work fabricated fully bio-based nanofibrous membrane with formaldehyde-adsorbable and antibacterial capabilities by electrospinning low-conductivity solution for high-performance air filtration and applied to lightweight mask. The "water-like" ethyl cellulose (EC) was selected as the base polymer to "nourish" functional materials of gelatin (GE), β-cyclodextrin (βCD), and curcumin (Cur), thus forming a solution system with high binding energy differences and electrospinning into ultrafine bimodal nanofibers. The filtration efficiency for 0.3 μm NaCl particles, pressure drop, and quality factor were 99.25 %, 53 Pa, and 0.092 Pa-1, respectively; the bacteriostatic rates against Escherichia coli and Staphylococcus aureus were 99.9 % and 99.4 %, respectively; the formaldehyde adsorption capacity was 442 μg/g. This is the first report on antibacterial and formaldehyde-adsorbable high-performance air filter entirely made from bio-based materials. This simple strategy will greatly broaden the selection of materials for preparing high-performance multifunctional air filter, and promote the development of bio-based air filter.

Osseointegration enhancement by controlling dispersion state of carbonate apatite in polylactic acid implant

Osteoconductive ceramics (OCs) are often used to endow polylactic acid (PLA) with osseointegration ability. Conventionally, OC powder is dispersed in PLA. However, considering cell attachment to the implant, OCs may be more favorable when they exist in the form of aggregations, such as granules, and are larger than the cells rather than being dispersed like a powder. In this study, to clarify the effects of the dispersion state of OCs on the osseointegration ability, carbonate apatite (CAp), a bone mineral analog that is osteoconductive and bioresorbable, powder-PLA (P-PLA), and CAp granule-PLA (G-PLA) composite implants were fabricated via thermal pressing. The powder and granule sizes of CAp were approximately 1 and 300-600 µm, respectively. G-PLA exhibited a higher water wettability and released calcium and phosphate ions faster than P-PLA. When cylindrical G-PLA, P-PLA, and PLA were implanted in rabbit tibial bone defects, G-PLA promoted bone maturation compared to P-PLA and pure PLA. Furthermore, G-PLA bonded directly to the host bone, whereas P-PLA bonded across the osteoid layers. Consequently, the bone-to-implant contact of G-PLA was 1.8- and 5.6-fold higher than those of P-PLA and PLA, respectively. Furthermore, the adhesive shear strength of G-PLA was 1.9- and 3.0-fold higher than those of P-PLA and PLA, respectively. Thus, G-PLA achieved earlier and stronger osseointegration than P-PLA or PLA. The findings of this study highlight the significance of the state of dispersion of OCs in implants as a novel strategy for material development.

The Rise of Electroactive Materials in Face Masks for Preventing Virus Infections

Air-transmitted pathogens may cause severe epidemics, posing considerable threats to public health and safety. Wearing a face mask is one of the most effective ways to prevent respiratory virus infection transmission. Especially since the new coronavirus pandemic, electroactive materials have received much attention in antiviral face masks due to their highly efficient antiviral capabilities, flexible structural design, excellent sustainability, and outstanding safety. This review first introduces the mechanism for preventing viral infection or the inactivation of viruses by electroactive materials. Then, the applications of electrostatic-, conductive-, triboelectric-, and microbattery-based materials in face masks are described in detail. Finally, the problems of various electroactive antiviral materials are summarized, and the prospects for their future development directions are discussed. In conclusion, electroactive materials have attracted great attention for antiviral face masks, and this review will provide a reference for materials scientists and engineers in antiviral materials and interfaces.

Preparation of fluffy bimodal conjugated electrospun poly(lactic acid) air filters with low pressure drop

Electrospun nanofiber membranes have been extensively studied as air filters. However, their limited filtration efficiency for submicron inhalable particulate matter (PM), high resistance to filtration, and limited capacity to hold dust have hindered their widespread use. The majority of materials come from petroleum, and the use of organic solvents during the spinning process has a significant negative impact on the environment. In this work, a sustainable method has been proposed for producing filters using poly(lactic acid) (PLA) with a bimodal diameter distribution through conjugated electrospinning. This technique allows for the continuous production of interconnected micro/nano hybrid porous membranes, resulting in reduced resistance and improved dust holding capacity. The filtration efficiency, pressure drop, long-term filtration performance, and actual performance of the conjugated bimodal membrane (CBM) were extensively investigated. The results indicate that the filter has a high capacity for retaining particles, with filtration efficiencies of 99.94% for PM 0.3 and 99.96% for PM 2.5. It also demonstrates a high quality factor (0.078 Pa-1 for PM 0.3 and 0.084 Pa-1 for PM 2.5), long-term stability (a decrease of 2.35% for PM 0.3 and 0.05% for PM 2.5 over a period of 60 days) and outstanding dust holding capacity (9.17 g m-2). The conjugated bimodal membrane (CBM) shows a 22.64% decrease in resistance compared to the non-conjugated bimodal membrane (BM). In general, the approach outlined in this work provides valuable insights into the development of high-performance biodegradable air filters. These filters have improved filtration efficiency and reduced resistance.

Production of Ultrafine PVDF Nanofiber-/Nanonet-Based Air Filters via the Electroblowing Technique by Employing PEG as a Pore-Forming Agent

Particles with diameters smaller than 2.5 μm (PM2.5) can penetrate the respiratory system and have negative impacts on human health. Filter media with a porous surface and nanofiber/nanonet structure demonstrate superior filtration performance compared to traditional nano- and microfiber-based filters. In this study, nanostructured filters were produced using the electroblowing method from solutions containing different ratios of poly(vinylidene fluoride) (PVDF) and polyethylene glycol (PEG) polymers for the first time. By increasing the water-soluble PEG ratio in PVDF/PEG blend nanofibers and employing a water bath treatment to the produced mat afterward, a more porous fibrous structure was obtained with a lower average fiber diameter. Notably, the removal of PEG from the PVDF/PEG (3-7) sample, which had the highest PEG content, exhibited clustered nanofiber-/nanonet-like structures with average diameters of 170 and 50 nm at the points where the fibers intersect. Although this process resulted in a slight decrease in the filtration efficiency (-1.3%), the significant reduction observed in pressure drop led to a 3.2% increase in the quality factor (QF). Additionally, by exploiting the polarizability of PVDF under an electric field, the filtration efficiency of the nanostructured PVDF filters enhanced with a ratio of 3.6% after corona discharge treatment leading to a 60% improvement in the QF. As a result, the PVDF/PEG (3-7) sample presented an impressive filtration efficiency of 99.57%, a pressure drop (ΔP) of 158 Pa, and a QF of 0.0345 Pa-1.

Nanopatterned Electroactive Polylactic Acid Nanofibrous MOFilters for Efficient PM0.3 Filtration and Bacterial Inhibition

Biodegradable polylactic acid (PLA) nanofibrous membranes (NFMs) hold great potential to address the increasing airborne particulate matter (PM) and dramatic accumulation of plastic/microplastic pollution. However, the field of PLA NFM-based filters is still in its infancy, frequently dwarfed by the bottlenecks regarding relatively low surface activity, poor electroactivity, and insufficient PM capturing mechanisms. This effort discloses a microwave-assisted approach to minute-level synthesis of dielectric ZIF-8 nanocrystals with high specific surface area (over 1012 m2/g) and ultrasmall size (∼240 nm), which were intimately anchored onto PLA nanofibers (PLA@ZIF-8) by a combined "electrospinning-electrospray" strategy. This endowed the PLA@ZIF-8 NFMs with largely increased electroactivity in terms of elevated dielectric coefficient (an increase of 202%), surface potential (up to 5.8 kV), and triboelectric properties (output voltage of 30.8 V at 10 N, 0.5 Hz). Given the profound control over morphology and electroactivity, the PLA@ZIF-8 NFMs exhibited efficient filtration of PM0.3 (97.1%, 85 L/min) with a decreased air resistance (592.5 Pa), surpassing that of the pure PLA counterpart (88.4%, 650.9 Pa). This was essentially ascribed to realization of multiple filtration mechanisms for PLA@ZIF-8 NFMs, including enhanced physical interception, polar interactions, and electrostatic adsorption, and the unique self-charging function triggered by airflow vibrations. Moreover, perfect antibacterial performance was achieved for PLA@ZIF-8, showing ultrahigh inhibition rates of 99.9 and 100% against E. coli and S. aureus, respectively. The proposed hierarchical structuring strategy, offering the multifunction integration unattainable with conventional methods, may facilitate the development of biodegradable long-term air filters.

Preparation and characterization of novel poly (lactic acid)/calcium oxide nanocomposites by electrospinning as a potential bone tissue scaffold

Calcium oxide nanoparticles (n-CaO) ca. 22 nm were obtained from eggshell waste. The n-CaO was incorporated into the PLA matrix in 10 and 20 wt% of filler content by electrospinning process to get PLA/n-CaO fibers with homogenous morphology and diameter as a potential use in scaffold for bone tissue regeneration. The incorporation of n-CaO into PLA modifies the mechanical properties, having a reinforcement effect on the matrix. The Young modulus for PLA/n-CaO nanocomposites increased between 122 and 138 % concerning neat PLA fibers, showing a more rigid behavior. The PLA/n-CaO nanocomposite fibers showed in vitro bioactivity, capable of inducing the precipitation of hydroxyapatite (HA) layer in the fiber surface after seven days in SBF solution. The biocidal and biological properties of PLA/n-Cao with 20 wt% showed a 30 % reduction in bacterial viability against S. aureus and 11 % against E. coli after 6 h of bacterial exposure. Furthermore, the fibers did not show a cytotoxic effect on the bone marrow ST-2 cell line, allowing cell adhesion and proliferation in the RPMI medium. The PLA/n-CaO with 20 wt% of nanoparticles showed a higher capacity to promote osteogenic differentiation, significantly increasing the alkaline phosphatase (ALP) expression after seven days compared to PLA and cell control. The in vivo analysis corroborated the biocompatibility of the prepared scaffolds; the presence of n-CaO in PLA reduced the formation of fibrous encapsulation of the material, improving the healing process. These results validated using n-CaO to enhance the functionality of polymer matrices as a PLA, bringing bioactive, biocide, and biocompatible properties, opening a new and interesting route to develop new biomaterials as a scaffold for bone tissue engineering.

Biodegradable Electroactive Nanofibrous Air Filters for Long-Term Respiratory Healthcare and Self-Powered Monitoring

The concept of triboelectric nanogenerator (TENG)-based fibrous air filters, in which the electroactive fibers are ready to enhance the electrostatic adsorption by sustainable energy harvesting, is appealing for long-term respiratory protection and in vivo real-time monitoring. This effort discloses a self-reinforcing electroactivity strategy to confer extreme alignment and refinement of the electrospun poly(lactic acid) (PLA) nanofibers, significantly facilitating formation of electroactive phases (i.e., β-phase and highly aligned chains and dipoles) and promotion of polarization and electret properties. It endowed the PLA nanofibrous membranes (NFMs) with largely increased surface potential and filtration performance, as exemplified by efficient removal of PM0.3 and PM2.5 (90.68 and 99.82%, respectively) even at the highest airflow capacity of 85 L/min. With high electroactivity and a well-controlled morphology, the PLA NFMs exhibited superior TENG properties triggered by regular respiratory vibrations, enabling 9.21-fold increase of surface potential (-1.43 kV) and nearly 68% increase of PM0.3 capturing (94.3%) compared to those of conventional PLA membranes. The remarkable TENG mechanisms were examined to elaborately monitor the personal respiration characteristics, particularly those triggered large and rapid variations of output voltages like coughing and tachypnea. Featuring desirable biocompatibility and degradability, the self-powered PLA NFMs permit promising applications in the fabrication of ecofriendly air filters toward high-performance purification and intelligent monitoring.