UVC-LED-based face mask design and efficacy against common germs

Figures 1–3 show the design of the face mask with detailed depiction of the UVC LED cartridges. The air is inhaled and exhaled through inlet and outlet air ducts in the cartridges whose air flow is adjusted with micro blowers to 5–10 L/min by changing the rotation speed.

Figure 1

Figure 2

Figure 3

Both inhaled and exhaled air are exposed to UVC light during the flow. The mask and the cartridges were designed with a Solidworks 3D CAD program (Dassault Systèmes SolidWorks Corporation, Waltham, MA, USA) and printed with a Flashforge Creator 3 3D printer (Zhejiang Flashforge 3D Technology Co., Ltd., Zehjiang, China) using the acrylonitrile-butadiene-styrene (ABS) filament for high durability.

For this study we designed two different cartridges. The first is a three-layer cartridge with a total of 30 UVC LEDs and the output of about 150 mW (30×5 mW/LED). To reduce the mask size, we then determined the minimum number of LEDs required for acceptable disinfection (Figure 2) by starting with all 30 UVC LEDs turned on and taking measurements, and then proceeding by turning off the LEDs one by one to eventually conclude that eight provided optimum efficiency. The second cartridge consists of only one layer with eight UVC LEDs (Figure 3), which we used for this study.

The UVC-LEDs we used are the Lekoled 3535 model (ShenZen, China) with a 275 nm emission wavelength and average radiant flux of 10 mW. They were powered by a battery (6.7 V, 80 mA for the three-layer cartridge and 6.7 V, 200 mA for the one-layer cartridge) and connected with a general-purpose LED driver circuit based on adjustable DC-DC converter with adjustable current designed in our laboratory.

Figure 4 shows the experimental setup for bacterial and viral determination. To generate aerosol, we used a general-purpose nebuliser (Nimomed, Denizli, Turkey) with a capacity to produce 15 L/min of aerosol of around 5 μm particle size. Air flow through the cartridge was adjusted to around 6 L/min to simulate normal breathing.

Figure 4

At the cartridge outlet the bacteria were trapped on the Whatman filter paper, and the viruses in cold serum-free Dulbecco's Modified Eagle's Medium (DMEM) (Merck, Darmstadt, Germany) at the bottom of Falcon tubes. Fresh cultures of the Staphylococcus aureus and Pseudomonas aeruginosa strains were taken from the Istanbul University-Cerrahpaşa Faculty of Medicine Infection Control Laboratory and COVID-19 Diagnostic Laboratory and serially passaged in Mueller Hinton agar as described elsewhere (16). A suspension containing 10⁶ CFU/mL of bacteria was cultivated in a sterile saline solution and this suspension placed in the nebuliser chamber.

To determine bacterial contamination, we removed the filters located at the cartridge output and transferred to 50 mL Falcon tubes containing 5 mL of sterile saline solution. After two minutes of vortexing, we took 100 mL of liquid from the tubes and inoculated blood agar (Laborlar Biotecnology, Istanbul, Turkey), CHROMagar (Laboratorios Conda S.A., Madrid Spain), and MacConkey agar media (Biolab Diagnostics Laboratory Inc., Budapest, Hungary). The combined use of these three media provides a versatile toolset for the identification, isolation, and analysis of a wide range of microorganisms (17, 18). Blood agar supports the growth of challenging microorganisms and is used for assessing haemolysis reactions in standard in vitro microbiological analyses (excluding living cells). CHROMagar enables fast and reliable identification of various pathogenic microorganisms based on their colour. MacConkey agar is used to isolate gram-negative enteric bacteria and distinguish those lactose-fermenting from nonlactose-fermenting. After 24 h, we counted the colonies.

Influenza A/Puerto Rico/8/1934 (PR8) strain was propagated in Madin Darby Canine Kidney (PMID: 34960614) (MDCK) (Biosys, Karben, Germany) cells grown at 37 °C in 5 % CO₂ Dulbecco's Modified Eagle's Medium (DMEM) (Merck, Darmstadt, Germany) supplemented with 10 % foetal bovine serum (FBS) (Merck, Darmstadt, Germany), 100 units/mL of penicillin, and 100 μg/mL streptomycin. The virus was identified and its 50 % tissue culture infectious dose (TCID50) (PMID: 32458296) determined in 96-well plates containing 1 % FBS and confirmed by Rt-qPCR assays (artus^® Infl./H1 LC/RG RT-PCR kit; Qiagen, Germany) run with a Rotor-Gene Q Series 2.1.2-build 9 software (Qiagen N.V., Venlo, the Netherlands).

The virus stock containing 1×10⁷/mL TCID₅₀ was diluted tenfold in cold, serum-free DMEM. A total of 4 mL medium containing the diluted virus was aerosolised in a sterile 50 mL Falcon tube, passed through the cartridge, and captured at the outlet in a 15 mL Falcon tube containing 4 mL of cold serum-free DMEM. Viral titre was determined by virus titration assays (19). All the experiments were repeated twice.

UV light can generate ozone, especially when the wavelength is below 240 nm, by breaking the bonds of oxygen molecules (20). Although the wavelength used in this study is 275 nm, we measured ozone to make sure that none were produced in the process. Ozone was measured at the cartridge outlet with the Indigo colour test, a passive visual technique based on colour change, using a Draeger ozone tube (Ozone 10/a, Drägerwerk AG & Co. KGaA, Lübeck, Germany).