Performance Comparison among KN95-Certified Face Masks by Classical Techniques and Innovative Test

Round 1

Reviewer 1 Report

Please see enclosed file

Comments for author File: Comments.pdf

Author Response

Referee #1

I read this paper as a specialist in infection control and not a medical engineer. Therefore, my comments should be interpreted in the light of my point of view. The study is of great interest, especially considering its practical implications, that is to say the possibility to enhance rapidly the safety of exposed individuals in the healthcare and social settings. The introduction is quite long, however, for the readers who are not expert in all the covered fields, which are many, it is undoubtedly interesting and clear, and it allows the readers to follow each step. I was able to understand the situation in which the study was conceived, the doubts and uncertainties which still exist in the way of transmission of “respiratory” diseases, the problems in selecting appropriate protection, the important features of respirators, the mechanisms of filtration, the differences in the certification standards and so on.

We would like to thank a lot the reviewer for his/hers polite comments about our submitted manuscript, above all considering his/hers area of expertise which confers an added value to our work. The manuscript was intended as a “meeting point” among different specialties applied to a tangible issue such the safety of exposed individuals and we feel flattered by the received comments on the clearness of the paper.

I strongly suggest to change all the sentences in which the Authors state their object, starting from the abstract, as it is not “the object of the paper” but “the object of the study”. You did a study to rapidly evaluate new masks appearing on the market in a moment of shortage of previously validated PPE.

We have changed the text accordingly, as it true that the most important thing we focused on was the study and, consequently, the paper.

As a reader, I would appreciate to read the following: Methods, 2.2 (novel MB method): is it feasible in other settings? How long does is take to set up the system? Is it expensive?

The newly developed method, which was not thoroughly discussed in the present paper (details are reported in reference 31), is quite simple, even though the most important part of the set-up is the pneumatic lung simulator, an instrument that is able to simulate the human breathe; this is likely the most expensive part of the equipment. We did not test different settings but the overall equipment is light and small, so it can be moved without difficulties; the nebulization was performed on a methylene blue solution but potentially many other solutions could be employed with this test (dyes but also other chemicals or even biological markers). Everything should just be calibrated prior to the test. Finally, the time is not a limiting factor, because as the equipment can be easily moved, it can be considered as always ready to be switched on and tested; of course, some time is required for the test itself (30 min) to get a satisfactory sensitivity and discriminate the different samples.

2.3 and 2.4: you did the morphological study to further explain and support your results with the MB test, is it right? These tests are not easy to carry out, the equipment to examine the layers structure and assess BFE of the masks in such detail is not available everywhere. Please provide a brief description of the setting in which these tests were carried out (e.g.” a collaboration between the hospital and the University...”) and in the conclusions, I would add a sentence suggesting that such collaborations may be of benefit in helping persons in charge of PPE selection to take more scientific, quality- based decisions when needed.

Exactly, we performed the morphological test, as well as the others to give scientific value to our findings obtained with the MB test and of course this was possible thanks to interdisciplinary collaborations among different Departments of the University and the Hospital, present in the same Italian city (Genova). As suggested, this feature was also added throughout the text and in the conclusion section.

Morphology 289-290: this sentence should be moved to the methods section. BFE 332-334: this sentence should be moved to the methods section.

We thank the reviewer for the suggestion; the text was modified accordingly.

Results and discussion

Results are not easy to read, especially the part on morphology, and the details and figures should be used to somehow support the MB results. Indeed, these tests are not essential for the new method, as I understood from your paper, but they provide additional features and evaluation of the various masks. Try to be clear at the beginning of each new paragraph in the results. Maybe an overall paragraph summarizing the tests results in the Conclusions section would be of help, e.g. filtering efficiency, breathability, hydrophobicity, BFE...giving the overall performance and the differences (“Although all the masks performed well in x and y, filtering efficiency showed significant differences as well as breathability. These differences are likely to be explained by the intermediate layer thickness, as well as by...”)

Authors agree on this issue: the strength of the present study was the interdisciplinary approach; on the other side it was not easy to merge all the results in the most proper way. We partly modify the manuscript, trying to be clearer in our explanations and conclusions.

Lines 256-261: I understood that: either the KN95 certification is not able to discriminate the diffusion of small droplets OR the label is a fake. Is this what you meant? As you are introducing a new method, I would use more caution, and suggest that further tests could be done: how many samples did you test for each mask? Is it possible that you took a “bad” sample and that not all masks from a manufacturer have the same features and performance? Anyway, also in the Conclusions (lines 370-371), I would rather say that the performance of the masks should be further explored and tested, even when these are certified, and not that it “cannot be guaranteed”. “Our method allows to better select appropriate protective equipment”. Provide details on how long did it take to perform the tests, i.e. how rapidly you decided which PPE to select, or how to decide which PPE to select.

We thank the reviewer for his/hers constructive comments. We tested all the samples received, then we decided to push a little bit our observations and this is the reason why we reported our conclusions on the possibility that the KN95 label could be not enough for such differences or otherwise that the label could have been imputed illegitimately. Sure, further tests should be performed in a systematic way to gain stronger information, but we took as an assumption that each tested mask provided by the manufacturer was representative and significant, as we didn’t have the possibility to choose the samples among all the mask production of each manufacturer. As reported in paragraph 2.2, three samples for each received mask were subjected to the MB method, which is a good starting point for characterizing single masks but still not enough to describe the features of all manufactured masks. All these considerations were used to modify the manuscript properly, especially in our conclusive remarks and in the selected lines reported by the reviewer.

Keywords should be added to allow specialists in infection control looking for methods to select PPE, to retrieve your article (add also “respirators”).

The keyword “respirators” has been added.

Reviewer 2 Report

Comments to applsci-1862100-peer-review-v1

 

This paper has comprehensively demonstrated the performance of the newly developed testing method in discrimination of the filtering capability of an array of KN95-certified face masks in comparison with the established standard. The manuscript is well-written and contains a good description of the methods and materials used. I would recommend the publication of the paper after the following issues are addressed.

 

1.     Could the author mention why sample 1, 4, 6 and 9 were eventually chosen for further morphological study? Just for a better understanding of the readers..

2.     Could the author present an illustration or picture of the MB test setup?

3.     In the BFE test, I would expect more discussion on the comparison of the MB test and the established BFE test. Does the author intend to replace the BFE test with the sampler MB test method? Thus I wonder what is the correspondence between these two standards. To which inhaled fraction (threshold), can represent the failure of the BFE test? It would be interesting to have a corresponding table to describe the result conversion.

4.     The author concluded that the intermediate layer thickness can be somehow correlated to the inhaled fraction obtained with the MB method. Could you give the statistical analysis (like ANOVA) on this comparison?

Comments for author File: Comments.docx

Author Response

Referee #2

This paper has comprehensively demonstrated the performance of the newly developed testing method in discrimination of the filtering capability of an array of KN95-certified face masks in comparison with the established standard. The manuscript is well-written and contains a good description of the methods and materials used. I would recommend the publication of the paper after the following issues are addressed.

We would like to thank the reviewer for his/hers positive comments on our manuscript. We tried our best to address every issue highlighted during the report.

1. Could the author mention why sample 1, 4, 6 and 9 were eventually chosen for further morphological study? Just for a better understanding of the readers.

We decided to perform further morphological characterization on a selected set of samples focusing on two samples that gained the best outcomes (1, 4), one intermediate (9) and the worst result with the MB method (6) to try to understand which physical-chemical characteristic could be imputed to the MB results. We tried to modify the test to be clearer on this point, either in “Materials and Methods” and in “Results and Discussion”.

2. Could the author present an illustration or picture of the MB test setup?

Authors decided to report as a reference the paper where the development of the new method was initially described. In particular, reference [31] shows such a picture.  

3. In the BFE test, I would expect more discussion on the comparison of the MB test and the established BFE test. Does the author intend to replace the BFE test with the sampler MB test method? Thus I wonder what is the correspondence between these two standards? To which inhaled fraction (threshold), can represent the failure of the BFE test? It would be interesting to have a corresponding table to describe the result conversion.

 

We would like to thank the reviewer for the interesting comment. The two characterization methods employ completely different “active materials”, i.e., a dye aqueous solution and a bacterial solution, which intrinsically behave differently as the former doesn’t require specific condition to keep the bacteria alive and the latter gives specific information depending on the type o microorganisms employed. We do not intend to replace the BFE test, used for validation of surgical masks and not for KN95 masks, according to the standard procedure UNI EN 14683:2019. In this study, the BFE test was used as a method of comparison and also “confirmation” of the MB test results. However, the Andersen-type impactor used for the BFE test is designed so that all airborne particles collected, regardless of physical size, shape, or density, are evaluated according to an aerodynamic dimension and can be correlated with penetration and deposition capacity in the human respiratory system. So, the aerodynamic diameter, corresponding to the effective cut off, for which 50% of the particles are stopped by the last stage of impact and 50% are allowed to pass (D50), is 0.65 µm. We added this last information in the BFE section.

4. The author concluded that the intermediate layer thickness can be somehow correlated to the inhaled fraction obtained with the MB method. Could you give the statistical analysis (like ANOVA) on this comparison?

The statistical analysis would represent a great tool to determine the correlation between the outcome of the MB method and the physical features of each mask. Nevertheless, we didn’t perform it because, as said in the manuscript, this represent a preliminary study; many factors influence the filtering process (both intermediate layer thickness and total weight seem to be involved) and further measurements are required to clarify how they affect it. At this stage, we can simply conclude that a face mask composed of multiple layers, the intermediate one of which being with a high density of fibers, can ensure high performances for the filtration mechanism.