Problem statement
Surgical masks are common personal protective equipment used in healthcare settings. In practice, however, these masks’ effectiveness in protecting the wearer from airborne diseases is limited by their loose fit on the face and frequent incorrect usage. Typical examples of the latter include wearers touching the contaminated outside of the mask, and wearing the mask for a prolonged period such that excessive humidity builds up and compromises the mask’s filtering performance. Especially now with the coronavirus outbreak, a global shortage of surgical masks is forcing their improper use, increasing contamination risks.
Proposed Solutions
To address problems stated above, we worked on two projects that are based on simple add-ons to improve the mask’s fit and promote proper usage.
Foam project
In the first project, solutions to improve the conformation of the mask to the face of the wearer are considered. We decided to explore the use of a functionalized polypropylene foam which would be added to the mask under the eyes and on the cheek to increase sealing effects. To functionalize the foam, cationic surfactants, Benzalkonium Chloride, are adsorbed on the polypropylene fibers. The positive charges on the surfactants interact with the negative charges present on micro-organisms’ surface. The foam thus acts as a filter that traps bacteria and viruses by electrostatic attraction. [1]
The selection of the materials followed two major criteria. First, the materials must be biocompatible as they are in direct and prolonged contact with the skin. Secondly, surgical masks are the most commonly used masks and must stay affordable. Therefore, the price of the add-on should be as low as possible. Polypropylene is the major compound of surgical masks and a cheap material. Benzalkonium Chloride is a common component of hand sanitizer. It is FDA approved to use in contact with the skin and has a proven antibacterial and antiviral activity. [2-3] This last characteristic increases further the efficiency of the filter.
To estimate the cost of the add-on, we built a prototype using cotton wool as foam. A volume of 30 cm3 was estimated to be sufficient to seal correctly the gaps between the mask and the skin. The polypropylene filter is composed of 75%/vol of fiber and 25%vol of air. The price of polypropylene fiber is 1920 euro/m3. [4] A mass of 160 mg/mask of Benzalkonium Chloride is sufficient to achieve good filtering capacity. The price of Benzalkonium Chloride is 140 euro/kg. [5]
(30x10-6 x 0.75 x 1920) + (160x10-6 x 140) = 0.065 euro
The cost of raw material used in the polypropylene foam is lower than 0.07 euro.
The manufacturing process is very simple and cheap. Polypropylene fibers are soaked in a solution of Benzalkonium Chloride 10mM during 3 hours. They are then vacuum dried and washed with water. [1]
The comfort for users is also improved as the foam is a soft and breathable material. It is therefore expected that less adjustments will be needed, reducing improper touching of the mask.
In order to examine the efficiency of the implemented modifications, a testing protocol has been established. First of all, redesigned masks should be tested according to standardized criteria given by the ASTM F2100 [9] and EN 14683 [10] norms in order to verify that foam deposition does not affect the surgical mask’s initial protection ability. Moreover, bearing in mind that comfort improvement was identified as one of the main objectives of the project, a detailed survey will be undertaken. Finally, Benzalkonium Chloride biocompatibility in long term usage should be confirmed using test protocols imposed by ISO 10993 norm.
Standardized tests according to ASTM F2100 and EN 14683 norms
-Bacteria filtration efficiency in vitro (BFE)[12]: Considering the antibacterial effect of the surfactant an increase of the filtration capacity is expected.
-Particle Filtration Efficiency: This test involves spraying an aerosol of polystyrene microspheres to ensure the mask can filter the size of the particle it’s supposed to.
-Breathing resistance [12]: To ensure that the foam deposition does not affect the breathability.
Splash resistance: To test foam aptitude to capture liquid.
-Flammability test: To ensure quick fire extinction.
Obtained results are compared to standard requirements[13].
The biocompatibility should be verified by a cytotoxicity (via MTT cell viability assay test protocol) and inflammation (by analysis of released pro inflammatory markers) tests[11]. Comfort surveys should be conducted in 2 parts, according to the instructions below : Wearer will be asked to evaluate mask’s comfort on a -4 to +4 scale (where -4 corresponds to a extrem;y uncomfortable and +4 very comfortable) During a limited amount of time the number of times the carrier needs to readjust his mask will be recorded.
Each survey will be compared to a control group of non-modified mask carriers.
Then, to consider potential reuse, the sterilization of the surgical masks was looked over.
As the mask and padding are made of polypropylene, relatively low heat (lower than 135°C) must be used to avoid potential damages. Because of the foam on the edges of the mask, the procedure should not deposit any dangerous residues. The sterilization should be fast, dry and low cost.
Following these concerns two methods were selected : UV sterilization and Ozone sterilization [10]
-UV sterilization: The method is based on damaging of cells by UV light. It is fast, cheap but the efficiency depends on the thickness of the material [7].
-Ozone sterilization: This procedure uses UV light to create ozone, which kills microorganism. It is fast, cheap, efficient but can damage the material after 10-100 cycles [8].
To select a sterilization procedure, preliminary tests must be carried. First, the effect of each method on the material has to be examined to ensure that it doesn’t lower its filtration capacity. Then, it should be verified that the procedure actually sterilizes the mask, by looking at the number of bacteria on the mask and the foam, when the mask is unused (positive control), worn for a few hours (negative control) and after sterilization.
Humidity project
In the second project, the optimal usage surgical masks is considered. Wearing it for a prolonged time leads to exposing wearers at higher risks of contamination. On the other hand, unnecessary change is a waste especially when they are in shortage. To tackle these problems, a color-changing indicator is proposed to alert the wearer when it is time to change the mask.
To figure out where the indicator should be placed, we first looked at LPAC microscope observations of the three-layer structure of surgical masks. The pictures taken show that the filter layer is a dense mesh of polypropylene fibers which will probably trap most of the humidity exhaled by wearers. If this is the case, the indicator would have to be placed inside the mask. To test for this, we conducted an experiment at home using pH paper and humidifiers. Our results show that moisture can go through the outer layer after 1.5 hours with water heated at 45°C. Although these tests are preliminary and further investigations are needed, our results suggest humidity measurement on the outer surface may be feasible. We therefore proceed with the color-changing humidity indicator design.
A potential candidate material for our humidity indicator is silica gel composite because it shows a large color change across a humidity scale and it is nontoxic [14]. The color gradually goes from green to purple across the dry state to over 60% relative humidity. The production of a silica gel composite film is simple and cost-effective. In fact, a series of chemical reactions involving different compounds like Tetraphenyporphirin (TPP), methanol and silica produce the humidity sensitive silica gel [15]. To minimize the influence of ambient humidity, the indicator is completely covered by water-impermeable single-sided tape cover and sticked on the outer layer of the surgical mask. A market research has been done to obtain the price of raw materials as shown in the table. The cost of raw materials used for a our humidity indicator is estimated to be only 10 cents:
SiO2 (25 g) + MeOH (12 g) + PCl2TPPCl (1.25 mg) + (1 mL) of MgCl2 (7.2 mM) + 3M tape = 0,095 euros of materials per mask [16].
Prices for the materials [17]
| Materials | Price |
|---|---|
| Industrial silicate graded (SiO2) | 2,59 euros/kg |
| Industrial methanol (MeOH) pure at 99% | 0,46 euros/kg |
| Tetraphenylporphyrin TPP | 0,05 euros/kg |
| Phosphoril Chloride (POCl3) | 0.13 euros/cm3 |
| MgCl2 | 0.25 euros/kg |
| Pyridine | 0,05 euros/cm3 |
| 3M Flexible Air Sealing Tape 8069E | 25 mm * 25 m = 53 euros |
Three characterization tests will be performed for our humidity indicator. With a breathing simulator, moisture distribution will first be quantified on the mask’s outer surface to optimize indicator placement. Secondly, the stand-alone indicator will be characterized in a controlled humidity chamber. Finally, the indicator will be integrated with the mask and tested with the breathing simulator. If the experimental results show the indicator is not sensitive enough, a potential improvement is to add wicks which can facilitate moisture transport from inside the mask through capillarity. With these tests we expect to characterize the indicator response to the mask humidity and gain understanding of how ambient conditions may affect the color readouts.
The influx of patients due to COVID-19 has placed our medical staff at higher risk. With our additions, we ensure that these masks are low cost, easy to use, maskimal protection.
Maskimal protection for a maskimal safety
Bibliography:
1: Huang, J. and Huang, V., 2007. Evaluation of the Efficiency of Medical Masks and the Creation of New Medical Masks. Journal of International Medical Research, 35(2), pp.213-223.
2: Bondurant, S., McKinney, T., Bondurant, L. and Fitzpatrick, L., 2019. Evaluation of a benzalkonium chloride hand sanitizer in reducing transient Staphylococcus aureus bacterial skin contamination in health care workers. American Journal of Infection Control,.
3: Rabenau, H., Kampf, G., Cinatl, J. and Doerr, H., 2005. Efficacy of various disinfectants against SARS coronavirus. Journal of Hospital Infection, 61(2), pp.107-111.
4: CES Edupack 2019 (Granta Design Limited, 2019)
5: Merck GaA, accessed the 06.04.2020 https://www.sigmaaldrich.com/catalog/product/sial/12060?lang=fr®ion=FR&cm_sp=Insite-_-prodRecCold_xviews-_-prodRecCold10-3
6: https://www.en-standard.eu/une-en-14683-2019-ac-2019-medical-face-masks-requirements-and-test-methods/ [Read on 06.04.2020]
7: Meunier, S.M., Sasges, M.R., and Aucoin, M.G. (2017). Evaluating ultraviolet sensitivity of adventitious agents in biopharmaceutical manufacturing. J. Ind. Microbiol. Biotechnol. 44, 893–909.
8: Bertoldi, S., Farè, S., Haugen, H.J., and Tanzi, M.C. (2015). Exploiting novel sterilization techniques for porous polyurethane scaffolds. J. Mater. Sci. Mater. Med. 26, 182.
9: https://www.astm.org/Standards/F2100.htm accessed the 06.04.2020.
10: Rutala, W.A., and Weber, D.J. (2016). Disinfection, sterilization, and antisepsis: An overview. Am. J. Infect. Control 44, e1–e6.
11: Hande Sipahi*, Filiz Esra Onen Bayram, Saziye Sezin Palabiyik, Dilara Bayram, Ahmet Aydın, Pteridines 2018. Investigation of Biocompatibility of Surgical Masks.
12: BSI Standards Publication. Medical face masks-Requirements and test methods.
13: Values of requirements of different tests from 3M company, accessed the 06.04.2020 https://multimedia.3m.com/mws/media/1791500O/comparison-ffp2-kn95-n95-filtering-facepiece-respirator-classes-tb.pdf
14: Fueda, Yoshiyuki, et al. "Porphyrin/MgCl2/silica gel composite as a cobalt-free humidity indicator." Chemistry letters 36.10 (2007): 1246-1247.
15: Fueda, Yoshiyuki, et al. "Bactericidal effect of silica gel-supported porphyrinatophosphorus (V) catalysts on Escherichia coli under visible-light irradiation." Bulletin of the Chemical Society of Japan 79.9 (2006): 1420-1425.
16: Values of requirements of different tests from 3M company, accessed the 06.04.2020 https://multimedia.3m.com/mws/media/1791500O/comparison-ffp2-kn95-n95-filtering-facepiece-respirator-classes-tb.pdf
17: Prices for the materials needed for the humidity sensor :
https://www.selfadhesive.co.uk/3m-flexible-air-sealing-tape-8069e-fast-d-25mm-x-25mm.html
https://www.tcichemicals.com/eshop/en/hk/commodity/A5012/
https://french.alibaba.com/
Thumbnail image: https://uk.pcmag.com/healthandfitness/125374/apple-and-facebook-donate-face-masks-to-healthcare-workers
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