In December of 2019 the first cases of a novel coronavirus, named “SARS-CoV-2” or “COVID-19”, were reported in China. As the virus spread across the continent, it proved to be both highly contagious and highly virulent. Patients who were infected were suffering from acute respiratory distress (ARDS). By the middle of March, the World Health Organization had designated the COVID-19 outbreak as a pandemic. Reports of not only strained economies but also strained global healthcare systems flooded the news. Within healthcare settings, the focus shifted to the adequacy of personal protective equipment (PPE).
PPE ShortagesThe shortage of PPE across the country has been widely discussed by government officials and healthcare practitioners as well as the general population. Unfortunately, recent reports indicate, “is running low again as the virus resumes its rapid spread and the number of hospitalized patients climbs.” Although the situation has improved since its inception earlier in the year, many experts predict that shortages persist. Additionally, some predict that it may take years in order for stockpiles to be fully replenished, a problem which presents an urgent challenges as cases continue to rise across the United States. Shortages of PPE have repeatedly been shown to contribute to the spread of the virus, and “the situation is especially dire at hospitals serving communities of color or patients on Medicaid.”
Fit TestingIn addition to PPE shortages, various studies have commented on challenges regarding inadequate mask fitting. Mask fit is an important consideration of mask efficacy and is typically measured by qualitative fit-tests (QLFT) or a quantitative fit-tests (QNFT). In qualitative fit-tests, mask wearers are tested to see if they can detect bitter or sweet scents aerosolized around the masked wearer whereas quantitative fit-tests measure ratios of ambient aerosols inside and outside of the mask. A 2018 Korean study reported QNFT pass rates of the four most common N95 models to be below 50%, with poorer fit test results observed for women compared to men. The inherent challenge of the possibility of a poor mask fit is magnified during pandemic settings due to time pressures and limited availability of options.
3D Printed AlternativesAs the aforementioned issues with PPE were playing out, communities of 3D printing aficionados, colloquially known as “makers” began to discuss the issue and created homemade masks, face shields, and gowns. Specifically, those with access to 3D printers were encouraged to continually run their machines to produce face-shields and masks that could be used in the health care sector. The lack of adequate access to conventional N95 masks pushed for some to pursue 3D printing and locally distributing masks as a possible avenue for stopgap PPE. The widespread availability of 3D printers and cost-effective nature of the manufacturing process makes it excellent for such purposes.
The mask presented, the Kansas City Mask (KC Mask), is one such mask born from the local maker community in partnership with local physicians and hospitals. This article discusses the design, manufacturing, and validation of the Kansas City mask design and its usage in the COVID-19 pandemic as well as future usage as stopgap PPE.
METHODSMask DesignThe Kansas City Mask is an N95 mask alternative consisting of two 3D printed parts shown in Figure 1 below.
Figure 1: KC Mask model -- both mask and filter-- loaded into Cura Slicer ready to be sliced and printed.As shown in Figure 1, the main component of the mask is that which makes contact with the mask wearers face. On the external face of that main component there is a 60mm x 60mm square hole where the second component, the filter holder, a 60mm x 60mm grid, will snap into place, holding in that space filter material. The filter material may be purchased through a third party or simply cut from Halyard H600 sterilization wrap which has shown to be N95 rated. In this study, Halyard H600 sterilization wrap was used.
The Kansas City Mask was adapted from a similar design called the Montana Mask. The goal of this redesign was to address some shortcomings of the Montana Mask, namely ease of breathing and fit. The Montana Mask has a smaller filter cross sectional area, making it more difficult to breath. Additionally, the Kansas City mask is meant to be heat molded to the wearers face to ensure a proper fit. This fit is additionally enhanced by the dipping process explained in its respective section.
Computer Automated Design and 3D PrintingThe design was created in the Fusion360 computer automated design application. For 3D printing, a variety of printers and software are able to be used once the model is exported to a “.stl” file format. Specifically, the Lulzbot Taz5 and Cura Slicer were used in the testing and manufacturing of the KC mask. A variety of materials were tested, but Polylactic acid (PLA) was chosen given its melting point, ease of use, and cost effectiveness. Print settings shown in Figure 2 were used. However, these may vary based on software and printer. For most printers, the default PLA settings will be sufficient.
Figure 2: Print SettingsSelect Print Setting
Value
Layer Height
0.25mm
Wall Line Count
4
Top/Bottom Layers
4
Infill Density
20%
Printing Temperature (Nozzle)
205°C
Printing Temperature (Build Plate)
60°C
Dipping and FittingDipping is an optional process in which soft, malleable material is added to the rim of the mask which makes contact with the wearer’s face. This allows for a better seal as well as increased comfort. FlexSeal rubberized sealant liquid was used in testing, although other brands may be used as well. An optional dipping tray model is provided to help with this process. The goal is to coat the rim of the mask that will be touching the users face. Depending on the sealant material used, it may take 24 hours to cure.
After the mask is dipped, it must be molded to the wearer’s face. For PLA material, the easiest way to do this is to submerge the mask (including the filter holder, but without any filter material) in hot water (~60ºC). This allows for the PLA to become soft enough to mold, but the structure is maintained. The wearer should submerge the PLA for ~10 seconds and mold it to fit their face. This can be repeated until a good and comfortable fit is achieved.
Fit TestingThe KC Mask was fit tested at Truman Medical Center in Kansas City, MO with the help of resident physician Dr. Brandon Bacon and the excellent facilities staff. A standard qualitative fit test (QLFT) was performed using standard saccharin solution aerosol protocol.
UsageElastic straps are used to secure the mask to the wearer’s face. In Figure 3, instructions for assembly and usage for the mask are discussed. This image is distributed alongside the mask as instructions for the user. These instructions include how to mold the mask, place the straps, and insert the filter. Sterilization of the mask is done using a Sani wipe or dilute bleach solution. Filters are meant to be only used once.
Figure 3: Assembly and Usage Instructions
IRB approval was not requested nor required for this study because this was essentially a proof of concept and quality improvement initiative. Although further analysis and study to prove efficacy is required, the purpose of this study and article is to discuss the design, manufacturing, and validation of the KC Mask concept.
RESULTSSeveral dozen masks were distributed to Truman Medical Center. As a proof of concept, Dr. Brandon Bacon donned the mask and performed a standard qualitative fit test (QLFT). The QLFT was successful and the KC Mask was approved for usage by staff at the hospital. The KC Mask was not widely utilized, however, because Truman Medical Center had adequate PPE supplies at the time.
DISCUSSIONThe results of Truman Medical Center’s approval of the KC Mask are promising for this N95 alternative. More extensive testing can and should be done, including quantitative fit testing. However, the initial results suggest that this mask could be efficacious at a larger scale. A recent study showed that of those who passed quantitative fit testing (QLFT) (N = 463) with all N95 FFR models, 86.9% (N = 459) also passed quantitative fit testing. This suggests that qualitative fit testing, although less rigorous than quantitative fit testing, is highly correlated with proper mask fitment.9
Although further analysis and study is needed for this design, persistently increasing caseloads and PPE shortages necessitates an urgent dissemination of these preliminary results. The authors do not advocate for the KC Mask as a replacement of traditional N95 masks or other PPE but do endorse the KC Mask as a stopgap measure, proven to be effective in situations of dire PPE shortage.
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Shiv Dalla
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