Hollow fiber membranes efficiently remove synthetic SARS-CoV-2 from the air

Airborne transmission is considered one of the primary factors contributing to the spread of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease (COVID-19). This remains particularly true in the current scenario where more transmissible SARS-CoV-2 variants like the Delta and Omicron strains are in circulation.

The need for highly effective and low-pressure filter technologies is essential to remove aerosols in indoor environments like restaurants, convention halls, and hospitals to effectively reduce viral transmission, primarily through respiratory droplets.

Study: Demonstration of Hollow Fiber Membrane-Based Enclosed Space Air Remediation for Capture of an Aerosolized Synthetic SARS-CoV-2 Mimic and Pseudovirus Particles. Image Credit: NokkieVector / Shutterstock.com

Background

Aside from purifying the air from contaminated bioaerosols, the removal of suspended particulate pollutants from the air is also imperative. In fact, particulate matter measuring 2.5 micrometers (μm) or smaller in diameter may also carry viral aerosols, thus increasing the risk of severe COVID-19.

Conventional polymer materials can be easily modified to improve surface functionalization and adjust membrane-surface properties. Furthermore, these materials can be modified through the addition of adding specific enzymes or nanoparticles in order to enhance their surface functionality. Controlling the thickness, pore size, structure, and porosity of polymer materials can help control the transport properties of the membrane and reduce the cut-off for filtering viruses more effectively.

Hollow fiber membranes (HFMs) are cylindrical, semipermeable membranes where transport occurs radially across the membrane. HFMs are an ideal solution for high-throughput scenarios due to their cylindrical geometry with a high surface area to volume ratio. To this end, HFMs can retain large filtration areas into small footprints while remaining effective for low-pressure operations.

No study to date has demonstrated viral aerosol capture using HFM modules with differing properties. As a result, researchers in a recent ACS ES&T Engineering study demonstrate their efforts to re-design the HFM filters and innovate methods for removing/deactivating viral aerosols, which could be cheaper alternatives to high-efficiency particulate air (HEPA) filtration systems with higher aerosol removal efficiency than standard heating, ventilation, and air conditioning (HVAC) filtration.

About the study

The current study investigated three hollow fiber membrane (HFM) modules for viral aerosol separation in enclosed spaces.

All tubing connections and valves were made of brass or stainless steel. Aerosol size distributions were measured in inside diameter (I.D.) of approximately three inches. The polytetrafluoroethylene (PTFE) tube served as a depressurizing chamber to avoid pressure damage to the pump in the optical particle counter.

Pore structures were characterized by scanning electron microscopy. In addition, the particle removal efficiency was characterized using aerosols generated by a constant output collision atomizer from a defined mixture of three kinds of synthetic nanoparticles, including 50 nanometers (nm) lipoic acid-coated gold nanoparticles, 100 nm COOH-functionalized polystyrene latex nanoparticles, and 500 nm amine-functionalized polystyrene latex nanoparticles that also included fluorescent-labeled SARS-CoV-2 mimics.

Aerosol concentrations were measured using an optical particle counter operated in differential mode showing different aerosol sizes for a better understanding of particle size filtration.

HFM1, which consisted of polyvinylidene fluoride with pores within the range of 50−1300 nm, exhibited an efficiency within the range of 96.5−100% for aerosols between 0.3−3 micrometers (μm) in size at a flow rate of about 18.6 ± 0.3 standard liters per minute (SLPM). Comparatively, HFM2, which consisted of polypropylene with pores that were about 40 nm in size, and HFM3, which consisted of hydrophilized polyethersulfone with pores within the size range of about 140−750 nm, demonstrated efficiencies between 99.65−100% and 98.8−100% at flow rates of 19.7 SLPM and 19.4 SLPM, respectively.

The filters could produce clean air with minimal fouling when demonstrated using ambient aerosols over two days. Finally, the filtration efficiency of each module was evaluated with a vesicular stomatitis virus (VSV) aerosol, which acted as a pseudovirus to mimic SARS-CoV-2.

To this end, the HFM1, HFM2, and HFM3 filters demonstrated an efficiency of 99.3%, 99.8%, and 99.8%, respectively, in reducing active viral titers as a direct measure of removing viral particles and keeping ambient air pure.

Implications

Studies like these help provide innovative solutions for the purification of ambient air, particularly during the current COVID-19 pandemic, where aerosolized viral particles directly contribute to rises in transmission rates. The findings from the present study provided an insight into the aerosol separation efficiency of HFMs, while also highlighting the need for further studies on these membranes in real-world settings.