American University of Beirut

New research on masks could enhance protection against viral infection and reusability

​​​​​​​​​​​​​​​​​​​​​​​Safa Jafari Safa​​, ​Office of Communications, communications​​

As efforts continue to combat and protect individuals during the COVID-19 pandemic, an AUB team initiated research that salt-coats the outer layer of facial masks to further protect the wearer as well as others. It also enables the reuse of masks, thus decreasing a financial burden, which is particularly important during economically challenging times.

Mask or filters can currently be a source of cross-infection, re-aerosolization, and environmental contamination, as viruses/bacteria infectivity can be maintained on their fibers. As they stand, the current two-layer membrane offers personal protection, but only for a limited number of hours.

As the trapped viruses can survive for several hours and even up to a day, the contaminated masks may become a source of infection for the wearer; hence, they are often limited for single use. Possible re-aerosolization and release of the viruses to the environment can also take place with improper/unsafe disposal of the masks, increasing the amount of bio-hazardous waste.

A request to find solutions for durable safe masks was initiated by Dr. Jamal Hoballah, professor and chairperson of the Department of Surgery ​at AUB's Faculty of Medicine, and Dr. Issam El-Rassi​, assistant professor of clinical specialty at the same department. Professors of mechanical engineering at the Maroun Semaan Faculty of Engineering and Architecture (MSFEA), Dr. Nesreen Ghaddar and Dr. Kamel Ghali, collaborated with Dr. Ali Tehrani, associate professor of chemical engineering at MSFEA, in looking at various options by which the mask design can be improved for use in sterile environments. After several WebEx meetings and weighing the costs and available resources in April, they decided to move ahead with the idea of producing a cheap and effective mask outer layer that is highly resistant to the growth of microbes and therefore enhances mask reusability as well as providing higher protection from possible COVID-19 contamination.

The team built their research on a study published by Quan et al. (2017), where salt-coated filters were demonstrated to have remarkably higher filtration efficiency and fully protected mice against respiratory infections for 16 days. Viruses captured on salt-coated filters were reported to exhibit rapid loss of infectivity compared to a gradual decrease of presence and power on untreated filters. They concluded that salt-coated filters are proven to be highly effective in deactivating influenza viruses. 

The research group therefore decided to replace the outer layer of masks with a salt-coated layer to increase antimicrobial efficiency. The team focused on salt-treating nonwovens made of polypropylene that are washable and reusable and can be used for the production of masks and gowns. They tested three samples at Dr. Tehrani's chemical engineering research lab of untreated, treated, and combined (treated+untreated) masks. Material structure and properties were characterized by measuring the pore size distribution, air permeability, water repellency, and water contact angle.

The filtration efficiency of the salt-coated nonwoven fabric mask was determined experimentally using a small wind tunnel equipped with a fan supplying a flow rate similar to that of the pulmonary ventilation rate during sedentary activity . An aerosol particle generator was used to generate polydisperse particles in a size range of 0.5-1.5 µm, upstream from the samples.

Preliminary results showed that the treated double-layer nonwoven fabric mask offers a decrease in pore size and in air permeability or resistance to flow. The salt-coated mask showed an improvement in the particulate matter to capture efficiency and better filtration performance. For a size bin of 0.5-0.6 µm (close to that of COVID-19 virus), the salt-treated mask aerosol filtration efficiency was around 98.5% compared to a 38.3% for the untreated mask. When combining the untreated and treated masks, producing a new double-layer nonwoven fabric mask, filtration effectiveness was further enhanced to around 99.1% for the same particle size bin. This can be justified by the reduced pore size of the membrane and the reduced air permeability.COVID19 Research-Story-Series​The filters are currently under clinical study by an expert AUBMC team that includes Dr. Hoballah and Dr. El-Rassi, where the outer layer will be replaced with the salt-coated layer and will be clinically tested for use in operating rooms, expanding for public use on any mask at a later stage. The AUBMC team will oversee the clinical testing of antimicrobial efficiency of the two-layered mask using available and nonwoven fabric membranes.

The testing is ongoing with different salt concentrations in ethanol and repetitive measurements. The goal is to obtain the best results for filtration efficiency, durability, and multiple-use after re-treatment. Future experiments will include testing the filtration efficiency of the masks while accounting for the effect of a high relative humidity of the human breath. Drs. Ghaddar and Ghali are also testing different samples using different particle sizes to determine filtration efficiency, ease of use, pressure drop, and resistance to airflow to ensure that the two-layer mask not only offers protection but also allows ease of breathing.  Additional tests will be done on mask tightness and leakage using a breathing thermal manikin in the energy efficiency lab at Mechanical Engineering Labs, as well as the number of times such masks can be used before washing or replacing, and how humidity from human exhalation would affect filtration intensity.

“During times of pandemic, this method would be easy to implement and would reduce the demand for disposable masks. It is easy to prepare, would protect our doctors and health professionals from respiratory infections at a low cost, and can easily be expanded for public use," said Dr. Nesreen Ghaddar, who is also the director of the Munib and Angela Masri Institute of Energy and Natural Resources​ and Qatar Chair in Energy Studies.

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