Multistage-Split Ultrafine Fluffy Nanofibrous Membrane for High-Efficiency Antibacterial Air Filtration

Electrospun PA6 multi-stage structured nanofiber membrane with high filtration performance for oily particles

Oily particles pollution poses a tremendous threat to people's health, so it is urgent to develop air filtration materials with the ability of removing fine oily particles effectively. In this study, a nylon 6 multi-stage structured nanofiber membrane (PA6 MSNM) for effective air filtration of fine oily particles was designed and fabricated by adding a certain amount of tetrabutylammonium hexafluorophosphate (TBAHP) via one-step electrospinning. The PA6 MSNMs were composed of coarse trunk fibres and fine branching fibres. Benefiting from the properties of small pore size and high porosity, the resulting PA6 MSNMs exhibited high average filtration efficiency of 99.80% for oily aerosol particles of 0.20-4.59 μm, a low pressure drop of 251 Pa, and the high quality factor of 0.0248 Pa-1. More importantly, its filtration efficiencies for oily aerosol particles of 0.25 and 0.30 μm were up to 99.99% and 100.00%, respectively. It is expected that the multi-stage electrospun nanofiber membranes would have wide application prospects in air filtration, particularly for filtering oily particles.

Electroactive nanofibrous membrane with antibacterial and deodorizing properties for air filtration

Water vapor from respiration can severely accelerate the charge dissipation of the face mask, reducing filtration efficiency. Moreover, the foul odor from prolonged mask wear tends to make people remove their masks, leading to the risk of infection. In this study, an electro-blown spinning electroactive nanofibrous membrane (Zn/CB@PAN) with antibacterial and deodorization properties was prepared by adding zinc (Zn) and carbon black (CB) nanoparticles to the polyacrylonitrile (PAN) nanofibers, respectively. The filtration efficiency of Zn/CB@PAN for PM0.3 was > 99% and could still maintain excellent durability within 4 h in a high-humidity environment (25 ℃ and RH = 95%). Moreover, the bacterial interception rate of the Zn/CB@PAN could reach 99.99%, and it can kill intercepted bacteria. In addition, the deodorization rate of Zn/CB@PAN in the moist state for acetic acid was 93.75% and ammonia was 95.23%, respectively. The excellent filtering, antibacterial, and deodorizing performance of Zn/CB@PAN can be attributed to the synergistic effect of breath-induced Zn/CB galvanic couples' electroactivity, released metal ions, and generated reactive oxygen species. The developed Zn/CB@PAN could capture and kill airborne environmental pathogens under humid environments and deodorize odors from prolonged wear, holding promise for broad applications as personal protective masks.

Hyperbranched Polymer Induced Antibacterial Tree-Like Nanofibrous Membrane for High Effective Air Filtration

The air filtration materials with high efficiency, low resistance, and extra antibacterial property are crucial for personal health protection. Herein, a tree-like polyvinylidene fluoride (PVDF) nanofibrous membrane with hierarchical structure (trunk fiber of 447 nm, branched fiber of 24.7 nm) and high filtration capacity is demonstrated. Specifically, 2-hydroxypropyl trimethyl ammonium chloride terminated hyperbranched polymer (HBP-HTC) with near-spherical three-dimensional molecular structure and adjustable terminal positive groups is synthesized as an additive for PVDF electrospinning to enhance the jet splitting and promote the formation of branched ultrafine nanofibers, achieving a coverage rate of branched nanofibers over 90% that is superior than small molecular quaternary ammonium salts. The branched nanofibers network enhances mechanical properties and filtration efficiency (99.995% for 0.26 µm sodium chloride particles) of the PVDF/HBP-HTC membrane, which demonstrates reduced pressure drop (122.4 Pa) and a quality factor up to 0.083 Pa-1 on a 40 µm-thick sample. More importantly, the numerous quaternary ammonium salt groups of HBP-HTC deliver excellent antibacterial properties to the PVDF membranes. Bacterial inhibitive rate of 99.9% against both S. aureus and E. coli is demonstrated in a membrane with 3.0 wt% HBP-HTC. This work provides a new strategy for development of high-efficiency and antibacterial protection products.

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.

Ultrathin, ultralight dual-scale fibrous networks with high-infrared transmittance for high-performance, comfortable and sustainable PM0.3 filter

Highly permeable particulate matter (PM) can carry various bacteria, viruses and toxics and pose a serious threat to public health. Nevertheless, current respirators typically sacrifice their thickness and base weight for high-performance filtration, which inevitably causes wearing discomfort and significant consumption of raw materials. Here, we show a facile yet massive splitting eletrospinning strategy to prepare an ultrathin, ultralight and radiative cooling dual-scale fiber membrane with about 80% infrared transmittance for high-protective, comfortable and sustainable air filter. By tailoring antibacterial surfactant-triggered splitting of charged jets, the dual-scale fibrous filter consisting of continuous nanofibers (44 ± 12 nm) and submicron-fibers (159 ± 32 nm) is formed. It presents ultralow thickness (1.49 μm) and base weight (0.57 g m-2) but superior protective performances (about 99.95% PM0.3 removal, durable antibacterial ability) and wearing comfort of low air resistance, high heat dissipation and moisture permeability. Moreover, the ultralight filter can save over 97% polymers than commercial N95 respirator, enabling itself to be sustainable and economical. This work paves the way for designing advanced and sustainable protective materials.

Effect of different antibacterial agents doping in PET-based electrospun nanofibrous membranes on air filtration and antibacterial performance

In order to reduce the particulate matter pollution to human health in producing environments, series of polyethylene terephthalate/polyvinyl alcohol (PET/PVA) based nanofibrous membranes were fabricated and investigated the dust collection and antibacterial activity. Silver nanoparticles (AgNPs), berberine (Ber) and titanium oxide nanoparticles (TiO2NPs) were selected as antibacterial agents. These novel membranes were well-characterized using SEM, FTIR, TG, etc. techniques. Results of the dust filtration showed that PET/PVA/Ag membrane had the best filtration efficiency of 99.87% for sodium chloride (NaCl) and 99.89% for dioctyl sebacate (DEHS), held low pressure drop of 160.1 Pa for NaCl and 165.3 Pa for DEHS, and posed a high tensile strength of 4.91 MPa. The bacteriostasis studies exhibited that PET/PVA/TiO2 and PET/PVA/Ag membrane showed the highest bacteriological effect on Escherichia coli (98.7%) and Staphylococcus aureus (95.9%), respectively. Meanwhile, in vitro cytotoxicity test indicated no potential cytotoxicity existed in the cell culture process of these two antibacterial membranes. Moreover, the charge distribution in the nanofibers was increased by these antibacterial agents to improve the filtration performance. The dust filtration process synergistically promoted with the antibacterial process in the antibacterial membranes. It was expected that these membranes could be efficient filter medias with broad application prospects in the field of individual protection.

Research on topological effect of natural small molecule and high-performance antibacterial air filtration application by electrospinning

The application of natural small molecule (NSM) in electrospun fibers is the key to achieving powerful functionality and sustainable development. However, the lack of understanding regarding the mechanism for loading NSM hinders the advancement of high-performance functional fibers. This work clarified the loading mechanism of NSM in polymer solution by comparing the different behaviors of curcumin (Cur), phloretin (PL), and tea polyphenols (TP) blended ethyl cellulose (EC) solutions. We found that TP may lead to the folding of polymer chains due to its strongest hydrogen bond, which in turn promoted the dispersion of TP along the polymer chain. Therefore, TP could achieve good electrospinnability at the highest loading capacity (16 times the Cur and 4 times the PL). Finally, chitosan was introduced into EC/TP to prepare tree-like nanofibers, achieving high-performance antibacterial air filtration. The filtration efficiency for 0.3 μm NaCl particles, pressure drop, and quality factor were 99.991 %, 85.5 Pa, and 0.1089 Pa-1, respectively. The bacteriostatic rates against Escherichia coli and Staphylococcus aureus were all 99.99 %. This work will promote the application of NSM and the developments of multifunctional electrospun fibers and high-performance air filters.

One-Step Fast Fabrication of Electrospun Fiber Membranes for Efficient Particulate Matter Removal

Rapid social and industrial development has resulted in an increasing demand for fossil fuel energy, which increases particulate matter (PM) pollution. In this study, we employed a simple one-step electrospinning technique to fabricate polysulfone (PSF) fiber membranes for PM filtration. A 0.3 g/mL polymer solution with an N,N-dimethylformamide:tetrahydrofuran volume ratio of 3:1 yielded uniform and bead-free PSF fibers with a diameter of approximately 1.17 μm. The PSF fiber membrane exhibited excellent hydrophobicity and mechanical properties, including a tensile strength of 1.14 MPa and an elongation at break of 116.6%. Finally, the PM filtration performance of the PSF fiber membrane was evaluated. The filtration efficiencies of the membrane for PM2.5 and PM1.0 were approximately 99.6% and 99.2%, respectively. The pressure drops were 65.0 and 65.2 Pa, which were significantly lower than those of commercial air filters. Using this technique, PSF fiber membrane filters can be easily fabricated over a large area, which is promising for numerous air filtration systems.

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.

Polarity-dominated chitosan biguanide hydrochloride-based nanofibrous membrane with antibacterial activity for long-lasting air filtration

Facemasks play a significant role as personal protective equipment during the COVID-19 pandemic, but their longevity is limited by the easy dissipation of electrostatic charge and the accumulation of bacteria. In this study, nanofibrous membranes composed of polyacrylonitrile and chitosan biguanide hydrochloride (PAN@CGH) with remarkable antibacterial characteristics were prepared through the coaxial electrospinning process. Particulate matter could be efficiently captured by the fibrous membrane, up to 98 % or more, via polarity-dominated forces derived from cyano and amino groups. As compared commercial N95 masks, the PAN@CGH was more resistant to a wider variety of disinfection protocols. Additionally, the nanofibrous membrane could kill >99.99 % of both Escherichia coli and Staphylococcus aureus. Based on these characteristics, PAN@CGH nanofibrous membrane was applied to facial mask, which possessed an excellent and long-lasting effect on the capture of airborne particles. This work may be one of the most promising strategies on designing high-performance face masks for public health protection.

Coaxial Electrospun Tai Chi-Inspired Lithium-Ion Battery Separator with High Performance and Fireproofing Capacity

Organic flame-retardant-loaded battery separator offers a new opportunity for battery safety. However, its poor thermal stability still poses serious safety issues. Inspired by Tai Chi, an "internal-cultivating and external-practicing" core-shell nanofibrous membrane was prepared by coaxial electrospinning, wherein the shell layer was a mixture of polyvinylidene fluoride, silicon dioxide (SiO2), and graphene oxide (GO) and the core layer contained triphenyl phosphate (TPP). SiO2 and GO enhanced the thermal stability and electrochemical performance. The encapsulated TPP prevented heat transfer and the degradation of electrochemical performance caused by its direct dissolution. This separator exhibited outstanding thermal stability and flame retardancy: it did not burn and remained relatively intact (91.2%) in an open flame for 15 s. The battery assembled with a composite separator showed excellent performance: the initial capacity reached 164 mA h/g and maintained 95% after 100 charge-discharge cycles. This novel strategy endows high-performance lithium batteries with relatively higher safety.

Guar gum-based multilayer fiber membranes inspired by plant transpiration for enhancing the functionality of dry facial masks

As more eco-friendly and economical choice for wet facial masks, dry facial masks have always had the problem of cumbersome application process and poor water retention property. In this study, based on the mechanism of directional water transport of Janus membrane and plant transpiration, the hydrophobic polylactic acid (PLA) nanofiber layer and the superhydrophilic guar gum (GG) nanofiber layer were prepared on both sides of the silk facial mask (SM) by electrospinning to obtain the guar gum-based bionic Janus directional water transport facial mask (G-DFM). The results showed that the directional water transport function improved the facial mask's water retention by 37 %, and the nicotinamide (NAM) encapsulated in the GG layer gave the facial mask excellent whitening and antibacterial properties. The GG layer could be directed to swell after absorbing water to form the "gel-like", which ensured that the G-DFM could continue to release NAM during its work and would enhance the attachment between the G-DFM and the skin. G-DFM not only retained the advantages of SM but also expanded the functions that SM did not have, providing an idea for designing more practical and ideal facial masks in the future.

Electroactive, Antibacterial, and Biodegradable Poly(lactic acid) Nanofibrous Air Filters for Healthcare

Poly(lactic acid) (PLA)-based nanofibrous membranes (NFMs) hold great potential in the field of biodegradable filters for air purification but are largely limited by the relatively low electret properties and high susceptibility to bacteria. Herein, we disclosed a facile approach to the fabrication of electroactive and antibacterial PLA NFMs impregnated with a highly dielectric photocatalyst. In particular, the microwave-assisted doping (MAD) protocol was employed to yield Zn-doped titanium dioxide (Zn-TIO), featuring the well-defined anatase phase, a uniform size of ∼65 nm, and decreased band gap (3.0 eV). The incorporation of Zn-TIO (2, 6, and 10 wt %) into PLA gave rise to a significant refinement of the electrospun nanofibers, decreasing from the highest diameter of 581 nm for pure PLA to the lowest value of 264 nm. More importantly, dramatical improvements in the dielectric constants, surface potential, and electret properties were simultaneously achieved for the composite NFMs, as exemplified by a nearly 94% increase in surface potential for 3-day-aged PLA/Zn-TIO (90/10) compared with that of pure PLA. The well regulation of morphological features and promotion of electroactivity contributed to a distinct increase in the air filtration performance, as demonstrated by 98.7% filtration of PM_0.3 with the highest quality factor of 0.032 Pa^-1 at the airflow velocity of 32 L/min for PLA/Zn-TIO (94/6), largely surpassing pure PLA (89.4%, 0.011 Pa^-1). Benefiting from the effective generation of reactive radicals and gradual release of Zn²⁺ by Zn-TIO, the electroactive PLA NFMs were ready to profoundly inactivate Escherichia coli and Staphylococcus epidermidis. The exceptional combination of remarkable electret properties and excellent antibacterial performance makes the PLA membrane filters promising for healthcare.

Electrospun nanofibers for medical face mask with protection capabilities against viruses: State of the art and perspective for industrial scale-up

Face masks have proven to be a useful protection from airborne viruses and bacteria, especially in the recent years pandemic outbreak when they effectively lowered the risk of infection from Coronavirus disease (COVID-19) or Omicron variants, being recognized as one of the main protective measures adopted by the World Health Organization (WHO). The need for improving the filtering efficiency performance to prevent penetration of fine particulate matter (PM), which can be potential bacteria or virus carriers, has led the research into developing new methods and techniques for face mask fabrication. In this perspective, Electrospinning has shown to be the most efficient technique to get either synthetic or natural polymers-based fibers with size down to the nanoscale providing remarkable performance in terms of both particle filtration and breathability. The aim of this Review is to give further insight into the implementation of electrospun nanofibers for the realization of the next generation of face masks, with functionalized membranes via addiction of active material to the polymer solutions that can give optimal features about antibacterial, antiviral, self-sterilization, and electrical energy storage capabilities. Furthermore, the recent advances regarding the use of renewable materials and green solvent strategies to improve the sustainability of electrospun membranes and to fabricate eco-friendly filters are here discussed, especially in view of the large-scale nanofiber production where traditional membrane manufacturing may result in a high environmental and health risk.

Effect of Matrix Metalloproteinase 23 Accelerating Wound Healing Induced by Hydroxybutyl Chitosan

Skin wounds may cause severe financial and social burden due to the difficulties in wound healing. Original inert dressings cannot meet multiple needs in the process of wound healing. Therefore, the development of materials to accelerate healing progress is essential and urgent. In the previous study, we found that the homogeneously synthesized hydroxybutyl chitosan (HBCS) had an effective performance in promoting wound healing. Proteomic analysis of the same specimen suggested that matrix metalloproteinase 23 (MMP23) may play a key role in HBCS expediting the progress of wound healing. In this work, we aim to reveal the underlying mechanism of MMP23 in the dynamic process of cutaneous proliferation and repair period. In order to regulate the expression level of MMP23 in the local wound area, we leaded in adeno-associated virus (AAV) to specifically decreased expression quantity of MMP23 in rat skin. In contrast to the negative control groups, we found that the wound closed faster and the collagen fibers and neovascularization were significantly increased in AAV groups. These findings highlighted that MMP23 was involved in wound healing after traumatic injury, and managing the expression of MMP23 could be a potential intervention target to accelerate wound healing.

Advanced functional nanofibers: strategies to improve performance and expand functions

Nanofibers have a wide range of applications in many fields such as energy generation and storage, environmental sensing and treatment, biomedical and health, thanks to their large specific surface area, excellent flexibility, and superior mechanical properties. With the expansion of application fields and the upgrade of application requirements, there is an inevitable trend of improving the performance and functions of nanofibers. Over the past few decades, numerous studies have demonstrated how nanofibers can be adapted to more complex needs through modifications of their structures, materials, and assembly. Thus, it is necessary to systematically review the field of nanofibers in which new ideas and technologies are emerging. Here we summarize the recent advanced strategies to improve the performances and expand the functions of nanofibers. We first introduce the common methods of preparing nanofibers, then summarize the advances in the field of nanofibers, especially up-to-date strategies for further enhancing their functionalities. We classify these strategies into three categories: design of nanofiber structures, tuning of nanofiber materials, and improvement of nanofibers assemblies. Finally, the optimization methods, materials, application areas, and fabrication methods are summarized, and existing challenges and future research directions are discussed. We hope this review can provide useful guidance for subsequent related work.

Graphical abstract

High-performance multifunctional electrospun fibrous air filter for personal protection: A review

With the increasingly serious air pollution and the rampant coronavirus disease 2019 (COVID–19), preparing high–performance air filter to achieve the effective personal protection has become a research hotspot. Electrospun nanofibrous membrane has become the first choice of air filter because of its small diameter, high specific surface area and porosity. However, improving the filtration performance of the filter only cannot meet the personal needs: it should be given more functions based on high filtration performance to maximize the personal benefits, called, multifunctional, which can also be easily realized by electrospinning technology, and has attracted much attention. In this review, the filtration mechanism of high–performance electrospun air filter is innovatively summarized from the perspective of membrane. On this basis, the specific preparation process, advantages and disadvantages are analyzed in detail. Furthermore, other functions required for achieving maximum personal protection benefits are introduced specifically, and the existing high–performance electrospun air filter with multiple functions are summarized. Finally, the challenges, limitations, and development trends of manufacturing high–performance air filter with multiple functions for personal protection are presented.

Modulation of Macrophages Using Nanoformulations with Curcumin to Treat Inflammatory Diseases: A Concise Review

Curcumin (Cur), a traditional Chinese medicine extracted from natural plant rhizomes, has become a candidate drug for the treatment of diseases due to its anti-inflammatory, anticancer, antioxidant, and antibacterial activities. However, the poor water solubility and low bioavailability of Cur limit its therapeutic effects for clinical applications. A variety of nanocarriers have been successfully developed to improve the water solubility, in vivo distribution, and pharmacokinetics of Cur, as well as to enhance the ability of Cur to polarize macrophages and relieve macrophage oxidative stress or anti-apoptosis, thus accelerating the therapeutic effects of Cur on inflammatory diseases. Herein, we review the design and development of diverse Cur nanoformulations in recent years and introduce the biomedical applications and potential therapeutic mechanisms of Cur nanoformulations in common inflammatory diseases, such as arthritis, neurodegenerative diseases, respiratory diseases, and ulcerative colitis, by regulating macrophage behaviors. Finally, the perspectives of the design and preparation of future nanocarriers aimed at efficiently exerting the biological activity of Cur are briefly discussed.