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3D printed and electrospun
To understand the reason behind the observation, As a result, we obtained a nanoporous PLA
we evaluated the pore size distribution of all self-reinforced structure that is transparent. The
the filters (Figure 4B). The results of the pore transparent look overcomes the threatening
size indicated that the average pore diameter of appearance of the masks that can be effective in
the filters with 210°C, 220°C, and 230°C was reducing the social trauma caused by the current
0.58, 0.62, and 0.81 μm, respectively. The pore CoV disease-19 pandemic. The transparency
structure was observed at the area between the can also allow lipreading which can reduce
printed struts, and it was primarily determined communication barrier to people with mutism or
by the electrospinning process instead of the hearing impairment when wearing mask. The all-
printing temperature. Therefore, we conclude PLA, self-reinforced structure renders the masks
that the higher filtration efficiency was resulted easy recyclability.
from the smaller pore size and not directly We explored the effects of nozzle temperature
related to the printing temperature. We further on the transmittance and mechanical properties
tested the filtration efficiency (in both [n%] of the filters developed. In comparison with the
and [wt.%]) by stacking multiple filter layers purely 3D printed mesh, the transmittance of the
(Supplementary file Tables 2-5). The results 3D printed filter was decreased, but they were still
we obtained are shown in Figure 4C. We found transparent with the transmittance around 20%.
that a significant increase in filtration efficiency Among the filters printed with different nozzle
was obtained with an increase in the number of temperatures, the filter printed at 210°C was the
layers. Especially for the filter with 230°C, its most transparent. The higher nozzle temperature
filtration efficiency was increased from 66.32 can increase the tensile strength and decrease
wt.% to 95.24 wt.%. One layer performs better the breaking strain because of the better fusion
than a surgical mask, and two-layered filters between the adjacent layers. One layer can perform
had a filtration efficiency of more than 80 wt.%, better than a classical surgical mask. Furthermore,
which is the criterion for FFP1 respirators. the multiple layer filter can have a similar filtration
Furthermore, when we stacked more than four performance as KN95/N95 and FFP2 filters. The
layers of the filters, all of them achieved the results are particularly useful for future mask filter
filtration efficiency of FFP2 (≥94 wt%). Some of studies. Instead of stacking the layers, we can try
them even had a similar filtration performance to print the filters with multiple nanofiber layers,
as KN95/N95 (≥95 wt%). In Figure 4D, we can which can to be further investigated.
observe the trapped particles on the surface of
the filter. The inset image shows that the printed Acknowledgments
filter was flexible and can be bent. The research reported in this paper was supported

5 Conclusions by the BME-Nanotechnology FIKP grant (BME
FIKP-NAT), the H2020-MSCA RISE No. 872152
In this study, we introduced a simple and facile - GREEN-MAP project of the European Union, the
method to combine nanofiber mats to a 3D printed ÚNKP-17-4-I New National Excellence Program
substrate successfully for making mask filters. of the Ministry of Human Capacities, and the
Our main concept is that nanofibers give excellent ÚNKP-19-4 New National Excellence Program
filtration, while the 3D printed structure supports of the Ministry for Innovation and Technology
the fibers to avoid their damage. This technique and BME-KKP. This paper was also supported
allows printing slightly flexible mask filters in any by the János Bolyai Research Scholarship of
shape achievable by 3D printing technology. The the Hungarian Academy of Sciences and the
custom production also allows us to fit the mask Stipendium Hungaricum Scholarship of Tempus
to any face shape or to put such filters in existing Public Foundation, and China Scholarship Council
masks. (201700500073).

8 International Journal of Bioprinting (2020)–Volume 6, Issue 4