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Salt Functionalization System for Protection against Airborne Diseases

  • Author / Creator
    Rubino, Ilaria
  • Infectious respiratory diseases, caused by viruses and bacteria that attack the respiratory system, constitute a serious threat in public health around the world. Pathogens can be transmitted in the air though large droplets or aerosols. As aerosols can linger in the environment for a prolonged time and travel long distances, airborne transmission causes fast and efficient transmission. Infection prevention plays a critical role against airborne particles in healthcare and for the public. In particular, respiratory protective devices, such as the commonly used N95 respirator and surgical mask, are the first line of defense during outbreaks and in susceptible settings. In spite of their indispensable function in infection control and emergency preparedness, masks have experienced limited progress over the years. Currently available masks exhibit unresolved technical challenges, including survival of the collected pathogens, filtration efficiency limited by breathability, and restriction to a single use of the devices. These lead to the risk of cross-infection from pathogen-laden filters, low effectiveness in infection prevention, low compliance to the recommended modes of use, and shortages of masks during outbreaks. Therefore, our research objective was the development of universal infection control measures against pathogenic aerosols. To this end, we successfully coated fibrous polymeric substrates with salt crystal films to produce highly effective, pathogen-inactivating filters.
    Formulations were identified to develop coatings based on different salt candidates, and formation of the salt coatings were confirmed by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. We hypothesized that salt coatings inactivate pathogens by first dissolving upon contact with the pathogenic aerosols, and then physically damaging the pathogens during the evaporation-induced salt recrystallization. For demonstration of the concept, surgical mask filters were coated with sodium chloride salt. Successful, quick pathogen inactivation was demonstrated both in vitro (by hemagglutinin activity (HA), virus titer, native fluorescence and nile red fluorescence measurements) and in vivo against aerosols of multiple strains of influenza virus. Additionally, our preliminary investigation showed that sodium chloride-coated filters have high filtration efficiency and stability after prolonged incubation at 37 °C and 70% relative humidity.
    Next, non-functional fibrous membranes were coated with uniform layers of sodium chloride, potassium sulfate and potassium chloride. The filtration efficiency tested against bacterial aerosols showed that the salt coatings turned the inert membranes into filters with high pathogen capture performance. Simultaneously, the pressure drop measured across the salt-coated filters at a breathing air flow did not increase compared the bare membranes. Following exposure to both virus and bacteria aerosols, all the developed salt coatings caused rapid pathogen inactivation, as measured by HA titer/virus titer and colony forming units (CFU) measurements, respectively. The physical damage on the pathogens was observed by transmission electron microscopy (TEM). Furthermore, the salt-coated filters were observed to be stable and functional following storage at 37 °C and 70, 80 and 90% relative humidity.
    Finally, the pathogen inactivation mechanism was analyzed by focusing on the interaction between salt powders and bacteria aerosols over time. It was observed that the salt recrystallization kinetics well matched the pathogen inactivation behaviors. Additionally, the salt recrystallization was observed to be the primary pathogen inactivation mechanism, although the high salt concentration during the aerosol evaporation was found to have a minor effect.
    Overall, this thesis has developed a technology for production of highly effective, low-cost infection control devices with universal pathogen inactivation and safe reusability, which can be used to tackle public health issues related to respiratory disease transmission worldwide.

  • Subjects / Keywords
  • Graduation date
    Fall 2020
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/r3-6xpz-n940
  • License
    Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.