Antiviral functionalization of a polypropylene nonwoven textile structure as a self-decontaminating layer for respiratory masks.

The aim of this work was to develop a filtering biocidal polypropylene (PP) nonwoven textile structure to block and inactivate airborne bacteria and viruses. PP filters were functionalized with a cyclodextrin (CD)-polycarboxylic acid-crosslinked polymer (PP-CD) through a pad/dry/curing process, and were then activated by padding in an alkyl dimethyl benzalkonium chloride (ADBAC) solution. The textile finishing process parameters were optimized with the perspective of mass production, considering the threshold temperature necessary for provoking crosslinking and the limitation of the low thermal stability of PP. The use of an aqueous solution containing hydroxypropyl-ß-cyclodextrin (HPßCD), 1,2,3,4-butanetetracarboxylic acid (BTCA), ammonium hypophosphite (AH), and a surfactant allowed immobilization of the optimal quantity of cyclodextrin polymer under curing for 5 minutes at 125 °C without affecting the nonwoven PP structure. The presence of CD drastically increased the sorption of ADBAC on the textiles. There was leaching of ADBAC at the first rinsing and then satisfactory fastness at the second and third rinsings, revealing adsorption mechanisms by weak physical interactions, ionic interactions, and inclusion of ADBAC inside the CD cavities. SEM revealed no clogging of the nonwoven pores, nor any increase in the air flow resistance, as evaluated by pressure drop measurements. The filtration efficiency of particulate matter PM3.0 and PM0.5 was moderately affected, in contrast to that of PM0.3, which greatly decreased due to the loss of the electrostatic charge of the filter upon the functionalization process. Bactericidal tests resulted in a reduction of 3 log10 against Staphylococcus aureus, and for virucidal tests on human coronavirus HCoV-229E, there was a reduction of 3.4 log10, with both strains undergoing 20 minutes of contact. Finally, the filter we developed is manufacturable by a scalable process, and because of its filtration and biocidal performances, it is a choice material as a self-disinfecting layer in the fabrication of facepiece respirators.

Biodegradable Electrospun Nanofiber Membranes as Promising Candidates for the Development of Face Masks.

Aerosol particles, such as the widespread COVID-19 recently, have posed a great threat to humans. Combat experience has proven that masks can protect against viruses; however, the epidemic in recent years has caused serious environmental pollution from plastic medical supplies, especially masks. Degradable filters are promising candidates to alleviate this problem. Degradable nanofiber filters, which are developed by the electrospinning technique, can achieve superior filtration performance. This review focuses on the basic introduction to air filtration, the general aspects of face masks, and nanofibers. Furthermore, the progress of the state of art degradable electrospun nanofiber filters have been summarized, such as silk fibroin (SF), polylactic acid (PLA), chitosan, cellulose, and zein. Finally, the challenges and future development are highlighted.

High-quality and easy-to-regenerate personal filter.

Proper respiratory tract protection is the key factor to limiting the rate of COVID-19 spread and providing a safe environment for health care workers. Traditional N95 (FFP2) respirators are not easy to regenerate and thus create certain financial and ecological burdens; moreover, their quality may vary significantly. A solution that would overcome these disadvantages is desirable. In this study a commercially available knit polyester fleece fabric was selected as the filter material, and a total of 25 filters of different areas and thicknesses were prepared. Then, the size-resolved filtration efficiency (40-400 nm) and pressure drop were evaluated at a volumetric flow rate of 95 L/min. We showed the excellent synergistic effect of expanding the filtration area and increasing the number of filtering layers on the filtration efficiency; a filter cartridge with 8 layers of knit polyester fabric with a surface area of 900 cm2 and sized 25 × 14 × 8 cm achieved filtration efficiencies of 98% at 95 L/min and 99.5% at 30 L/min. The assembled filter kit consists of a filter cartridge (14 Pa) carried in a small backpack connected to a half mask with a total pressure drop of 84 Pa at 95 L/min. In addition, it is reusable, and the filter material can be regenerated at least ten times by simple methods, such as boiling. We have demonstrated a novel approach for creating high-quality and easy-to-breathe-through respiratory protective equipment that reduces operating costs and is a green solution because it is easy to regenerate.

Pressure-dependent fouling behavior during sterile filtration of mRNA-containing lipid nanoparticles.

The COVID-19 pandemic has generated growing interest in the development of mRNA-based vaccines and therapeutics. However, the size and properties of the lipid nanoparticles (LNPs) used to deliver the nucleic acids can lead to unique phenomena during manufacturing that are not typical of other biologics. The objective of this study was to develop a more fundamental understanding of the factors controlling the performance of sterile filtration of mRNA-LNPs. Experimental filtration studies were performed with a Moderna mRNA-LNP solution using a commercially available dual-layer polyethersulfone sterile filter, the Sartopore 2 XLG. Unexpectedly, increasing the transmembrane pressure (TMP) from 2 to 20 psi provided more than a twofold increase in filter capacity. Also surprisingly, the effective resistance of the fouled filter decreased with increasing TMP, in contrast to the pressure-independent behavior expected for an incompressible media and the increase in resistance typically seen for a compressible fouling deposit. The mRNA-LNPs appear to foul the dual-layer filter by blocking the pores in the downstream sterilizing-grade membrane layer, as demonstrated both by scanning electron microscopy and derivative analysis of filtration data collected for the two layers independently. These results provide important insights into the mechanisms governing the filtration of mRNA-LNP vaccines and therapeutics.

Development of a combinatory filtration system for pollution and virus abatement by optimized nanoparticle deposition.

PM2.5, particulate matter less than 2.5 microns, is the leading contributor to air pollution which results in cardio-vascular and respiratory diseases. Recent studies also indicate a strong correlation between ambient air pollution and COVID-19 cases, which have affected the lives of billions of people globally. Abatement technologies such as ionic and other high efficiency filtration systems are expensive and unaffordable in communities with limited resources. The goal of this study was to develop a mask with an optimized nanoparticle coating which has a dual capability of particulate matter and virus filtration, while being affordable and safe for human use. The nanoparticles were selected for their filtration and virucidal capabilities. Particle filtration efficiency, tested with a wind tunnel and PM2.5 from incense sticks measured by laser particle detectors, improved by ~60% with nanoparticle coatings on KN95 and surgical masks. Virus filtration efficiency, tested using nebulized NaCl particles as a virus surrogate, improved by 95% with coated masks. The nanoparticle retention efficacy, tested by simulating a normal 8-hour workday, was well within the permissible exposure limits. This technology has several applications such as in personal protective equipment for virus protection, and in air-conditioning and car cabin filters for pollution abatement. In conclusion, the chosen combination of nanoparticles provides an effective and safe solution for both particulate matter and viral particle filtration.

Durable nanocomposite face masks with high particulate filtration and rapid inactivation of coronaviruses.

The COVID-19 pandemic presents a unique challenge to the healthcare community due to the high infectivity rate and need for effective personal protective equipment. Zinc oxide nanoparticles have shown promising antimicrobial properties and are recognized as a safe additive in many food and cosmetic products. This work presents a novel nanocomposite synthesis approach, which allows zinc oxide nanoparticles to be grown within textile and face mask materials, including melt-blown polypropylene and nylon-cotton. The resulting nanocomposite achieves greater than 3 log10 reduction (≥ 99.9%) in coronavirus titer within a contact time of 10 min, by disintegrating the viral envelope. The new nanocomposite textile retains activity even after 100 laundry cycles and has been dermatologist tested as non-irritant and hypoallergenic. Various face mask designs were tested to improve filtration efficiency and breathability while offering antiviral protection, with Claros' design reporting higher filtration efficiency than surgical masks (> 50%) for particles ranged 200 nm to 5 µm in size.

New insights into the standard method of assessing bacterial filtration efficiency of medical face masks.

Based on the current knowledge of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) transmission, wearing a mask has been recommended during the COVID-19 pandemic. Bacterial filtration efficiency (BFE) measurements enable designing and regulating medical masks to prevent bioaerosol dissemination; however, despite the simplicity of these measurements, several scientific questions remain unanswered regarding BFE tests. Here, we investigated (1) the impact of substituting 100-mm Petri dishes with 90-mm disposable Petri dishes, (2) the impact of colony-counting methods on the bioaerosol aerodynamic size, and (3) the impact of colony-counting methods on the total viable particle counts. We demonstrated that disposable 90-mm Petri dishes can be used to replace the 100-mm dishes. We also showed that an automatic high-resolution colony counter can be used to directly count viable particles on collection substrates and to measure the bioaerosol size parameters. Our results enable possible modernization of the outdated testing methods recommended in the US and European standards for BFE measurements. Specifically, use of a modernized colony counter should be clearly regulated and permitted to avoid the counting of positive holes. The median aerodynamic diameter appears to be the most relevant parameter for characterizing bioaerosol size.

The critical importance of mask seals on respirator performance: An analytical and simulation approach.

Filtering facepiece respirators (FFRs) and medical masks are widely used to reduce the inhalation exposure of airborne particulates and biohazardous aerosols. Their protective capacity largely depends on the fraction of these that are filtered from the incoming air volume. While the performance and physics of different filter materials have been the topic of intensive study, less well understood are the effects of mask sealing. To address this, we introduce an approach to calculate the influence of face-seal leakage on filtration ratio and fit factor based on an analytical model and a finite element method (FEM) model, both of which take into account time-dependent human respiration velocities. Using these, we calculate the filtration ratio and fit factor for a range of ventilation resistance values relevant to filter materials, 500-2500 Pa∙s∙m-1, where the filtration ratio and fit factor are calculated as a function of the mask gap dimensions, with good agreement between analytical and numerical models. The results show that the filtration ratio and fit factor are decrease markedly with even small increases in gap area. We also calculate particle filtration rates for N95 FFRs with various ventilation resistances and two commercial FFRs exemplars. Taken together, this work underscores the critical importance of forming a tight seal around the face as a factor in mask performance, where our straightforward analytical model can be readily applied to obtain estimates of mask performance.

A validated UHPLC-MS/MS method for rapid determination of senicapoc in plasma samples.

The clinically tested KCa3.1 channel blocker, senicapoc, has been proven to have excellent pharmacological properties and prior clinical trials found it to be safe for use in patients with sickle cell anaemia. Currently, several preclinical projects are aiming to repurpose senicapoc for other indications, but well-described analytical methods in the literature are lacking. Our aim was to develop a sensitive, rapid and accurate ultra-high-performance liquid chromatography-tandem mass spectrometry method using pneumatically assisted electrospray ionisation (UHPLC-ESI-MS/MS) suitable for the determination of senicapoc in plasma samples. Unfortunately, direct analysis of senicapoc in crude acetonitrile extracts of human plasma samples by UHPLC-ESI-MS/MS was subjected to significant and variable ion suppression from coeluting phospholipids (PLs). The interferences were mainly caused by the presence of phosphatidylcholine and phosphatidylethanolamine classes of PLs, including their lyso-products. However, the PLs were easily removed from crude extracts by filtration through a sorbent with Lewis acid properties which decreased the total ion suppression effect to approximately 5%. Based on this technique, a simple high-throughput UHPLC-MS/MS method was developed and validated for the determination of senicapoc in 100-µL plasma samples. The lower limit of quantification was 0.1 ng/mL. The mean true extraction recovery was close to 100 %. The relative intra-laboratory reproducibility standard deviations of the measured concentrations were 8% and 4% at concentrations of 0.1 ng/mL and 250 ng/mL, respectively. The trueness expressed as the relative bias of the test results was within ± 2% at concentrations of 1 ng/mL or higher.

Water-Repellent TiO2-Organic Dye-Based Air Filters for Efficient Visible-Light-Activated Photochemical Inactivation against Bioaerosols.

Recently, bioaerosols, including the 2019 novel coronavirus, pose a serious threat to global public health. Herein, we introduce a visible-light-activated (VLA) antimicrobial air filter functionalized with titanium dioxide (TiO2)-crystal violet (CV) nanocomposites facilitating abandoned visible light from sunlight or indoor lights. The TiO2-CV based VLA antimicrobial air filters exhibit a potent inactivation rate of ∼99.98% and filtration efficiency of ∼99.9% against various bioaerosols. Under visible-light, the CV is involved in overall inactivation by inducing reactive oxygen species production both directly (CV itself) and indirectly (in combination with TiO2). Moreover, the susceptibility of the CV to humidity was significantly improved by forming a hydrophobic molecular layer on the TiO2 surface, highlighting its potential applicability in real environments such as exhaled or humid air. We believe this work can open a new avenue for designing and realizing practical antimicrobial technology using ubiquitous visible-light energy against the threat of infectious bioaerosols.

SARS-CoV-2 indoor contamination: considerations on anti-COVID-19 management of ventilation systems, and finishing materials in healthcare facilities.

Abstract: Many of the devastating pandemics and outbreaks of last centuries have been caused by enveloped viruses. The recent pandemic of Coronavirus disease 2019 (COVID-19) has seriously endangered the global health system. In particular, hospitals have had to deal with a frequency in the emergency room and a request for beds for infectious diseases never faced in the last decades. It is well-known that hospitals are environments with a high infectious risk. Environmental control of indoor air and surfaces becomes an important means of limiting the spread of SARS-CoV-2. In particular, to preserve an adequate indoor microbiological quality, an important non-pharmacological strategy is represented by Heating, Ventilation and Air Conditioning (HVAC) systems and finishing materials. Starting from the SARS-CoV-2 transmission routes, the paper investigates the hospital risk analysis and management, the indoor air quality and determination of microbial load, surface management and strategies in cleaning activities, HVAC systems' management and filters' efficiency. In conclusion, the paper suggests some strategies of interventions and best practices to be taken into considerations for the next steps in design and management.

Roll-to-Roll Production of Spider Silk Nanofiber Nonwoven Meshes Using Centrifugal Electrospinning for Filtration Applications.

Filtration systems used in technical and medical applications require components for fine particle deep filtration to be highly efficient and at the same time air permeable. In high efficiency filters, nonwoven meshes, which show increased performance based on small fiber diameters (e.g., using nanofibers), can be used as fine particle filter layers. Nanofiber nonwoven meshes made by electrospinning of spider silk proteins have been recently shown to exhibit required filter properties. Needle-based electrospinning, however, is limited regarding its productivity and scalability. Centrifugal electrospinning, in contrast, has been shown to allow manufacturing of ultrathin polymer nonwoven meshes in an efficient and scalable manner. Here, continuous roll-to-roll production of nonwoven meshes made of recombinant spider silk proteins is established using centrifugal electrospinning. The produced spider silk nanofiber meshes show high filter efficiency in the case of fine particulate matter below 2.5 µm (PM2.5) and a low pressure drop, resulting in excellent filter quality.

Electrostatic Filters to Reduce COVID-19 Spread in Bubble CPAP: An in vitro Study of Safety and Efficacy.

BACKGROUND: Bubble CPAP may be used in infants with suspected or confirmed COVID-19. Electrostatic filters may reduce cross infection. This study aims to determine if including a filter in the bubble CPAP circuit impacts stability of pressure delivery. METHODS: A new electrostatic filter was placed before (pre) or after (post) the bubble CPAP generator, or with no filter (control) in an in vitro study. Pressure was recorded at the nasal interface for 18 h (6 L/min; 7 cm H2O) on 3 occasions for each configuration. Filter failure was defined as pressure >9 cm H2O for 60 continuous minutes. The filter was weighed before and after each experiment. RESULTS: Mean (SD) time to reach the fail point was 257 (116) min and 525 (566) min for filter placement pre- and post-CPAP generator, respectively. Mean pressure was higher throughout in the pre-generator position compared to control. The filter weight was heavier at end study in the pre- compared to the post-generator position. CONCLUSIONS: Placement of the filter at the pre-generator position in a bubble CPAP circuit should be avoided due to unstable mean pressure. Filters are likely to become saturated with water over time. The post-generator position may accommodate a filter, but regular pressure monitoring and early replacement are required.

How can we minimize the potential risk of viral contamination during laparoscopic procedures for suspected or infected COVID-19 patients?

Several societies have raised the risk of viral transmission of SARS-Cov-2 due to surgical smoke during laparoscopic procedures in infected patients. We propose to discuss this issue and to describe specific measures during laparoscopic procedures and a new homemade closed filtration system for smoke evacuation. Since the outbreak of COVID-19, performing a laparoscopy should meet multi-modal requirements. Surgical smoke evacuation device may be an effective tool in reducing exposure to surgical smoke and aerosols.

A laboratory-based study examining the properties of silk fabric to evaluate its potential as a protective barrier for personal protective equipment and as a functional material for face coverings during the COVID-19 pandemic.

The worldwide shortage of single-use N95 respirators and surgical masks due to the COVID-19 pandemic has forced many health care personnel to use their existing equipment for as long as possible. In many cases, workers cover respirators with available masks in an attempt to extend their effectiveness against the virus. Due to low mask supplies, many people instead are using face coverings improvised from common fabrics. Our goal was to determine what fabrics would be most effective in both practices. Under laboratory conditions, we examined the hydrophobicity of fabrics (cotton, polyester, silk), as measured by their resistance to the penetration of small and aerosolized water droplets, an important transmission avenue for the virus causing COVID-19. We also examined the breathability of these fabrics and their ability to maintain hydrophobicity despite undergoing repeated cleaning. Laboratory-based tests were conducted when fabrics were fashioned as an overlaying barrier for respirators and when constructed as face coverings. When used as material in these two situations, silk was more effective at impeding the penetration and absorption of droplets due to its greater hydrophobicity relative to other tested fabrics. We found that silk face coverings repelled droplets in spray tests as well as disposable single-use surgical masks, and silk face coverings have the added advantage over masks such that they can be sterilized for immediate reuse. We show that silk is a hydrophobic barrier to droplets, can be more breathable than other fabrics that trap humidity, and are re-useable via cleaning. We suggest that silk can serve as an effective material for making hydrophobic barriers that protect respirators, and silk can now be tested under clinical conditions to verify its efficacy for this function. Although respirators are still the most appropriate form of protection, silk face coverings possess properties that make them capable of repelling droplets.

Neuropathogens and Nasal Cleansing: Use of Clay Montmorillonite Coupled with Activated Carbon for Effective Eradication of Pathogenic Microbes from Water Supplies.

Herein, we propose the use of novel adsorbents, namely micelle clay complexes comprising the clay montmorillonite, coupled with activated carbon for effective eradication of neuropathogenic microbes such as SARS-CoV-2 and Naegleria fowleri from water supplies for ablution/nasal irrigation. These can be incorporated easily to water collection devices, i.e., taps and water bottles, in the domestic setting. These filters are low cost, easy to install, and ideal disinfection systems. Such strategies are particularly useful for communities who have lack of access to safe water supplies, rely heavily on water storage tanks, or lack adequate water sanitation facilities, especially in developing countries.

Filtration performances of non-medical materials as candidates for manufacturing facemasks and respirators.

The recent outbreak of the coronavirus disease (COVID-19) is causing a shortage of personal protective equipment (PPE) in different countries around the world. Because the coronavirus can transmit through droplets and aerosols, facemasks and N95 respirators that require complex certification, are urgently needed. Given the situation, the U.S. Centers for Disease Control and Prevention (CDC) recommends that "in settings where facemasks are not available, healthcare personnel might use homemade masks (e.g., bandana, scarf) for the care of patients with COVID-19 as a last resort." Although aerosols and droplets can be removed through the fibers of fabrics through a series of filtration mechanisms, their filtration performances have not been evaluated in detail. Moreover, there are a series of non-medical materials available on the market, such as household air filters, coffee filters, and different types of fabrics, which may be useful when facemasks and respirators are not available. In this study, we comprehensively evaluated the overall and size-dependent filtration performances of non-medical materials. The experiments were conducted under different face velocities to study its influence on size-dependent filtration performances. The flow resistance across these filter materials is measured as an indicator of the breathability of the materials. The results illustrate that multiple layers of household air filters are able to achieve similar filtration efficiencies compared to the N95 material without causing a significant increase in flow resistance. Considering that these air filters may shed micrometer fibers during the cutting and folding processes, it is recommended that these filters should be inserted in multiple layers of fabrics when manufacturing facemasks or respirators.

Design and evaluation of a portable negative pressure hood with HEPA filtration to protect health care workers treating patients with transmissible respiratory infections.

BACKGROUND: To mitigate potential exposure of healthcare workers (HCWs) to SARS-CoV-2 via aerosol routes, we have developed a portable hood which not only creates a barrier between HCW and patient, but also utilizes negative pressure with filtration of aerosols by a high-efficiency particulate air filter. MATERIAL AND METHODS: The hood has iris-port openings for access to the patient, and an opening large enough for a patient's head and upper torso. The top of the hood is a high-efficiency particulate air filter connected to a blower to apply negative pressure. We determined the aerosol penetration from outside to inside in laboratory experiments. RESULTS: The penetration of particles from within the hood to the breathing zones of HCWs outside the hood was near 10-4 (0.01%) in the 200-400 nm size range, and near 10-3 (0.1%) for smaller particles. Penetration values for particles in the 500 nm-5 µm range were below 10-2 (1%). Fluorometric analysis of deposited fluorescein particles on the personal protective equipment of an HCW revealed that negative pressure reduces particle deposition both outside and inside the hood. CONCLUSIONS: We find that negative pressure hoods can be effective controls to mitigate aerosol exposure to HCWs, while simultaneously allowing access to patients.