A recent Swiss study published on bioRxiv* The preprint server demonstrated that aerosol filters centered on granular protein nanofibrils and iron oxyhydroxide (Fe) nanoparticles could trap virus-containing aerosols.
Study: Trapping virus-laden aerosols using granular protein nanofibrils and iron oxyhydroxide nanoparticles. Image Credit: Dotted Yeti / Shutterstock
As the first line of defense against viral outbreaks and pandemics, non-pharmaceutical measures are crucial.
Using air filters has many advantages over other non-pharmaceutical measures against coronavirus disease 2019 (COVID-19), such as mask mandates and social distancing. They lead to the preservation of interior spatial capacities, constitute an economical alternative to insufficiently ventilated premises, and are less sensitive to individual choices or behavioral discipline.
The benchmark for aerosol filtering is the High Efficiency Particulate Filter (HEPA). The global deployment of HEPA filters to prevent the spread of airborne viruses in indoor environments will incur exorbitant financial and environmental costs.
Overall, stopping the transmission of airborne viruses has been quite difficult, and this difficulty increases if it is to be achieved comprehensively and sustainably.
About the study
In the current research, scientists have created an aerosol filter composed of a granular filtration material based on Fe oxyhydroxide nanoparticles and amyloid (AF) nanofibrils, i.e., AF-Fe, by adopting a simple production procedure.
FA was synthesized by lowering the pH to 2 and boiling whey protein extract, a derivative of the dairy industry, at 90°C for about five hours. The chemical properties of the AF-Fe material were confirmed using Fourier transform infrared spectroscopy. Additionally, mercury intrusion porosimetry was used to analyze the intra-particle pore size distribution of the material.
The authors designed and built a small experimental setup to test the filtration ability of the material. In this setup, virus-laden aerosols were generated, passed through AF-Fe at a flow rate of 7.5 L/min, and then captured on a gelatin membrane that traps ≥ 99% of passing viruses while retaining their infectivity. The filtration capacity of AF-Fe was assessed by comparing infectious viruses captured on gelatin membranes with and without AF-Fe.
Researchers examined the impact of reducing the amount of AF-Fe on pressure drop and filtration efficiency. After filtering aerosols containing bacteriophage MS2 or Φ6, they incubated the AF-Fe for approximately one hour in phosphate-buffered saline (PBS) to assess the safety of the material. In addition, the researchers modeled four of the most important aerosol trapping processes to deeply analyze how AF-Fe traps aerosols: diffusion, interception, gravitational sedimentation and impaction.
The results of the study showed that the AF-Fe material was environmentally friendly, biodegradable and a by-product of the dairy sector. According to sieve analysis, it has a wide size range, with half its mass less than 3 mm.
Fourier transform infrared spectroscopy showed three peaks for amide groups, representing amyloid fibrils, and one for the Fe-OH group, symbolizing Fe oxyhydroxide nanoparticles. The AF-Fe material had a high specific surface area, 44 .1m2/g, i.e., half the surface coverage potential of 1 g of AF-Fe was approximately 3*1012 and 7*1014 for 150 or 30 nm virus particles, respectively. In addition, its specific density, ρs, was 2.1 g/cm3and the bulk densities of the oven-dried and air-equilibrated samples were 1.4 and 1.7 g/cm3respectively demonstrating a reasonably high intra-particle porosity of 30% and a volumetric water content of 36%.
The AF-Fe material had pores ranging in size from tens to thousands of nanometers, according to mercury intrusion porosimetry. The size range of these pores allowed them to act as virus-trapping cavities once the viruses attached to the AF-Fe surface.
AF-Fe had an average filtering efficiency of 95.91% and 99.87% against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and H1N1, respectively. Both were enveloped viruses and were known to be airborne. For a non-enveloped enterovirus recognized for its stability and resistance to harsh chemical conditions, EV71, AF-Fe has a filtration efficiency of 99%. The average filtration efficiency for bacteriophage Φ6 was 99.99%, while for bacteriophage MS2 was 98.29%.
Surprisingly, the filtration efficiency was accompanied by a negligible pressure drop, i.e.
After crossing the AF-Fe, the ratio of SARS-CoV-2 to infectious H1N1 and the whole genome decreased, proving that the viruses were contained and partially inactivated. Nevertheless, EV71 did not exhibit such inactivation, supporting the fact that non-enveloped viruses were more resistant and robust to the mechanical stresses of AF-Fe interactions and the re-aerosolization procedure.
Since no infectious virus was recovered, the authors noted that AF-Fe rendered bacteriophage Φ6 completely inactive or irrevocably trapped the virus. Furthermore,
Together, the study results showed that AF-Fe filtered virus-laden aerosols with high efficiency while being environmentally friendly and sustainable. Additionally, the material exhibited surprisingly minimal pressure drop, suggesting low energy and operating costs.
In addition, the contaminated materials were safe to handle and had a significantly higher recycling potential than commercial filters available on the market. The team envisions the material being used to mitigate airborne viruses spread around the world with virtually no environmental footprint. The use of granular materials for aerosol filtration in the present study should encourage researchers to search for local, novel, and environmentally friendly materials that could serve as the basis for aerosol filters.
bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.
- Trap virus-laden aerosols using granular protein nanofibrils and iron oxyhydroxide nanoparticles; Antonius Armanious, Heyun Wang, Peter Alpert, Chiara Medaglia, Mohammad Peydayesh, Arnaud Charles-Antoine Zwygart, Christian Gübeli, Stephan Handschin, Sreenath Bolisetty, Markus Ammann, Caroline Tapparel, Francesco Stellacci, Raffaele Mezzenga. bioRxiv preprint 2022, DOI: https://doi.org/10.1101/2022.06.29.498082, https://www.biorxiv.org/content/10.1101/2022.06.29.498082v1