Next Generation Self-Sanitising Face Coverings: Nanomaterials and Smart Thermo-Regulation Systems

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript reviews the latest research advancements in the field of self-sanitizing masks achieved through thermal processes and nanomaterial incorporation—a topic of considerable importance and value that is increasingly attracting attention in both academic research and practical applications. To enhance the manuscript's potential for publication, several key areas require additional emphasis and refinement:

1. Introduction: The current discussion on masks appears somewhat fragmented and lacks a coherent structural framework. It is recommended to include:
• A comprehensive diagram that outlines the basic characteristics and classifications of masks.
• A table summarizing the advantages and disadvantages of various mask types, which would significantly aid readers in understanding the content.
2. Detachment of Nanoparticles (Pages 4–5): The discussion should address the release of nanomaterials from textiles and their potential implications for the human respiratory system. Certain antibacterial nanomaterials may not adhere securely after post-treatment, or their adhesion may weaken during heat treatment, leading to the detachment of nanoparticles. This detachment could pose direct risks to the respiratory system and warrants further exploration.
3. Clarity of Figure 2: The text within Figure 2 is insufficiently clear. It is recommended to optimize the figure to improve its readability and ensure that the information is effectively conveyed to the audience.
4. Main Text Discussion: In Section 3, the author highlights the inhalation risks associated with the shedding of nanoparticles from fibers. What specific recommendations does the author propose to mitigate this risk? Addressing this issue with practical suggestions would strengthen the discussion.
5. Reviewer’s Suggestion: The reviewer is investigating a production process that involves the direct co-embedding of nanoparticles (e.g., copper oxide, silver-copper bimetallic particles, or nano-copper oxide and nano-zinc oxide) within the fibers. This method has been shown to achieve 99% antimicrobial efficacy at relatively low antimicrobial concentrations (e.g., 100–500 ppm), in compliance with international standards. The manuscript would benefit from discussing the feasibility or potential of such methods in the context of self-sanitizing thermal masks.
6. Electrostatic Filtration Issues: For high-efficiency three-layer masks (e.g., N95 or N100), the reuse of meltblown nonwoven fabric(middle layer) may lead to the loss of surface charge, thereby compromising the electrostatic adsorption filtration function. For reusable self-sanitizing masks that incorporate heating or other reusable features, what solutions does the author propose to address this electrostatic filtration challenge? Providing insights or innovative approaches to this problem would greatly enhance the manuscript's practical relevance.

 

Author Response

We are grateful to the suggestions and comments provided by reviewers which has enhanced the quality of the manuscript. In the following sections, the authors have provided the detailed response, and the text is included in the manuscript with a different font colour.

 

1. Introduction: The current discussion on masks appears somewhat fragmented and lacks a coherent structural framework. It is recommended to include:
   1. A comprehensive diagram that outlines the basic characteristics and classifications of masks.
   2. A table summarizing the advantages and disadvantages of various mask types, which would significantly aid readers in understanding the content.

The introduction has been revised suitably to ensure that the contents flow well and is coherent. 

Table 1 has been added, highlighting the advantages and disadvantages of the various commercially available masks for various applications with illustration.  (see page 3, line 65)

S.No.	Image of mask	Description	Advantages	Disadvantages
Cloth Masks
01		Reusable medical cloth mask	Reusable and washable, with customisable and eco-friendly designs	Depending on the fabric, the filtering efficiency varies, and it is less efficient against aerosols.
Disposable Masks
02		Single-use blue disposable mask consumed by public	Cost-effective and convenient for one-time use in low-risk settings	Significant influence on the environment and insufficient protection against aerosols
Surgical Masks
03		White Surgical mask for medical use	Simple to manufacture, broadly accessible, pleasant for prolonged use, and providing minimal droplet protection	Single-use products have limited aerosol filtration, which adds to waste, and poor fit creates air leakage holes.
04		Single valve-based surgical mask
05		Dual valve-based surgical mask
N95 Respirators
06		N 95 surgical mask	High filtration efficiency (up to 95% of airborne particles are blocked) and a tight seal that reduces air leaking	Costly and uncomfortable to wear for extended periods of time
Nano-Finished Masks
07		Silver nano finished face mask	Antimicrobial properties with improved filtration, self-cleaning capabilities, and lightweight materials.	Possible release of nanoparticles that need careful handling and testing and have a higher production cost
Smart Masks
08		Smart Masks with thermoregulation system	It has sophisticated features, including sensors and heating elements, and is appropriate for extreme circumstances.	Expensive and requires complicated maintenance
Powered Air-Purifying Respirators (PAPRs)
09		Industrial respirators mask	Long-lasting and reusable, offering optimal protection, and comfortable for long periods of use	Costly, bulky, and require battery operation and maintenance

 

2. Detachment of Nanoparticles (Pages 4–5): The discussion should address the release of nanomaterials from textiles and their potential implications for the human respiratory system.

Nanomaterials are finished on fabrics using metal and metal oxides whose affinity of these          nanoparticles to the textile substrate depends on the concentration used, type of finishing, curing, usage, location, and overall handling. Hence, a certain percentage of leaching of nanoparticles is anticipated. Therefore, there are some implications for human health. However, it depends on the antimicrobial finishing and nanoparticles used. The above text was added in section 1 page 05, specifically in lines 96-103.

 

3. Certain antibacterial nanomaterials may not adhere securely after post-treatment, or their adhesion may weaken during heat treatment, leading to the detachment of nanoparticles. This detachment could pose direct risks to the respiratory system and warrants further exploration.

 

Nanoparticles should be rigorously evaluated for cytotoxicity against key mammalian cell lines, including skin, lungs, and the respiratory system. The level of leaching or detachment, if any, should be minimal. Standardised test methods evaluate the cytotoxicity and function of face coverings and materials (ISO10993-5:2009, In-vitro cytotoxicity tests for medical devices and ISO 16900-7:2020, Respiratory protective devices and methods for test and testing equipment) [Petrachi et al., 2021 and Mier et al., 2022].  The above text was added in section 2.2 page 11, specifically in lines 321-326.

 

In nano-finished face masks, the outer layer is a nano-finished fabric, while the middle and inner layers are not finished. The masks with thermal elements should be placed in the middle layer, which may penetrate the outer layer under prolonged use or high temperatures, potentially increasing nanoparticle release. However, the inner layer remains unaffected, mitigating the risk of direct contact with the human respiratory system. The above text was added in section 2.2 page 11, specifically in lines 335-341.

 

• Petrachi, T., Ganzerli, F., Cuoghi, A., Ferrari, A., Resca, E., Bergamini, V., Accorsi, L., Burini, F., Pasini, D., Arnaud, G. F., Piccini, M., Aldrovandi, L., Mari, G., Tomasi, A., Rovati, L., Dominici, M., & Veronesi, E. (2021). Assessing Biocompatibility of Face Mask Materials during COVID-19 Pandemic by a Rapid Multi-Assays Strategy. International Journal of Environmental Research and Public Health, 18(10), 5387. https://doi.org/10.3390/ijerph18105387
• Meier, P. et al. (2022) ‘Evaluation of fiber and debris release from protective COVID-19 mask textiles and in vitro acute cytotoxicity effects’, Environment International, 167, p. 107364. https://doi.org/10.1016/j.envint.2022.107364on the human respiratory system.

 

4. Clarity of Figure 2: The text within Figure 2 is insufficiently clear. It is recommended that the figure be optimised to improve its readability and ensure that the information is effectively conveyed to the audience.

 

Authors agree with the reviewer’s suggestion, Figure 2 has been suitably edited to improve its readability.

 

5. Main Text Discussion: In Section 3, the author highlights the inhalation risks associated with the shedding of nanoparticles from fibres. What specific recommendations does the author propose to mitigate this risk? Addressing this issue with practical suggestions would strengthen the discussion.

 

To mitigate the inhalation risks associated with the shedding of nanoparticles from fibres in smart thermo-regulation systems masks, the following recommendations may be taken into consideration: Development of advanced binding techniques or methods such as pad-dry-cure method or batch process (Venkatraman et al., 2022) enhances adhesive properties of nanoparticles on cotton-based substrate. In addition, layer-by-layer deposition (Carosio et al.0215), or using confined impinging jet mixer produces nanoparticles with functional compounds to ensure stronger adhesion of nanoparticles to the fabric (Ferri et al., 2017). On other hand, the ultrasound irradiation assisted water/oil/water microemulsion method with UV curing enhances antimicrobial properties (Ghayempour et al., 2017). By using these techniques, and positioning of nano-finished materials away from direct contact with the human respiratory system can prevent the inhalation risks of shaded nanoparticles. The above text was added in section 4 page 23, specifically in lines 679-687.

 

• Venkatraman, P. D., Sayed, U., Parte, S., & Korgaonkar, S. (2021). Development of Advanced Textile Finishes Using Nano-Emulsions from Herbal Extracts for Organic Cotton Fabrics. Coatings, 11(8), 939. https://doi.org/10.3390/coatings11080939
• Carosio, F.; Cuttica, D.; di Blasio, A.; Alongi, J.; Malucelli, G. Layer by layer assembly of flame retardant thin films on closed cell PET foams: Efficiency of ammonium polyphosphate versus DNA.  Degrad. Stab.2015, 113, 189–196. 
• Ferri, A.; Kumari, N.; Peila, R.; Barresi, A.A. Production of menthol-loaded nanoparticles by solvent displacement.  J. Chem. Eng.2017, 95, 1690–1706.
• Ghayempour, S.; Montazer, M. Tragacanth Nanocapsules containing chamomile extract prepared through sono-assisted W/O/W microemulsion and UV cured on cotton fabric.  Polym.2017, 170, 234–240.

6. viewer’s Suggestion: The reviewer is investigating a production process that involves the direct co-embedding of nanoparticles (e.g., copper oxide, silver-copper bimetallic particles, or nano-copper oxide and nano-zinc oxide) within the fibres. This method has been shown to achieve 99% antimicrobial efficacy at relatively low antimicrobial concentrations (e.g., 100–500 ppm), in compliance with international standards. The manuscript would benefit from discussing the feasibility or potential of such methods in the context of self-sanitizing thermal masks.

 

In page 10 section 2.2, authors have already reviewed the area of metal and metal oxides for textile applications; however, we have now expanded to include research on the embedding of copper oxides and added information in Table 3, page 11.  

 

One specific example would be when copper oxide was embedded into PAN (polyacrylonitrile), decreases in S. aureus and E. coli bacterial count of 10⁸ were observed when compared with untreated nanofibre controls (Fattahi et al., 2024).

 

The above text was added in section 2.2 page 10, specifically in lines 308-311.

• Fattahi, M. et al. (2024) ‘Evaluation of the efficacy of NanoPak Mask®: A polyacrylonitrile/copper oxide nanofiber respiratory mask’, Materials Today Communications, 38, p. 108129. doi:10.1016/j.mtcomm.2024.108129.

7. Electrostatic Filtration Issues: For high-efficiency three-layer masks (e.g., N95 or N100), the reuse of meltblown nonwoven fabric (middle layer) may lead to the loss of surface charge, thereby compromising the electrostatic adsorption filtration function. For reusable self-sanitizing masks that incorporate heating or other reusable features, what solutions does the author propose to address this electrostatic filtration challenge? Providing insights or innovative approaches to this problem would greatly enhance the manuscript's practical relevance.

 

This point is addressed in page 21, Section 3.4, specifically in lines 614-619, Finally, electrostatic adsorption filtration may be considered using triboelectric nanogenerators. The melt blown nonwoven fabrics which are normally used in the face masks as a mid-layer can be reused, provided its electrostatic charge can be restored via a triboelectric nanogenerators (TENG) recharging technique, by using polyamide nanofibre filter which offers electrostatic interaction between the particles and the filter (Vasquex-Lopez et al., 2023).

 

• Vázquez-López, A., Ao, X., del Río Saez, J. S., & Wang, D. Y. (2023). Triboelectric nanogenerator (TENG) enhanced air filtering and face masks: Recent advances. Nano Energy, 108635.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors reviewed the recent developments of functional nanomaterials with conductive polymeric materials, smart textiles that used in the next generation of face masks with high sensitivity and acting on air-borne viruses. I recommend this review for publication in this journal with minor revision.

1 How do the nanomaterials interact with microbial entities to reduce contamination, this discussion section may be shortly summarized in a Table.

2 Line 292 section 2.2, The metal oxide nanomaterials as finished materials for textile fabric, how do they function in textile is not explained very clearly.

3 Despite metal oxides, some metal nanomaterials, such as Ag, may be used in textiles. Did the authors take this into account?

4 Did the authors ever considered the potential biotoxicity of the nanomaterials used face masks?

Author Response

Reviewer 2 comments and authors responses:

 

We are grateful to the suggestions and comments provided by reviewers which has enhanced the quality of the manuscript. In the following sections, the authors have provided the detailed response, and the text is included in the manuscript with a different font colour.

 

1 How do the nanomaterials interact with microbial entities to reduce contamination; this discussion section may be shortly summarised in a Table.

In section 3.5, self-sanitisation test for nano-finished facemasks, provides a detailed analysis of how test methods to evaluate the filtration efficiency and anti-bacterial efficacy is enhanced preventing contamination. In addition, Table 7. Nanomaterials finished on different textile fabrics tested with different virus environments provides information of how different nanomaterials can be effective against various microbes and viruses.

Since the above is already included in the manuscript, no further text has been included.

2 Line 292 section 2.2, The metal oxide nanomaterials as finished materials for textile fabric, how do they function in textile is not explained very clearly.

 

Metal oxide nanoparticles, such as ZnO and TiO₂, enhance textiles by providing beneficial properties like UV protection, antibacterial activity, and self-cleaning properties.  The details on how metal oxide nanomaterials perform has been discusses in section 2.2 clearly. As it is already in the manuscript, no further explanation is offered.

 

3 Despite metal oxides, some metal nanomaterials, such as Ag, may be used in textiles. Did the authors take this into account?

 

Yes, the details are discussed in Section 2.1, “conductive metals as finished nanomaterials for textile fabric,” and are further elaborated in Table 2, which presents information on different conductive metals. As it is already in the manuscript, no further explanation is offered.

 

4 Did the authors ever consider the potential biotoxicity of the nanomaterials used in face masks?

 

Nanoparticles should be rigorously evaluated for cytotoxicity against key mammalian cell lines, including skin, lungs, and the respiratory system. The level of leaching or detachment, if any, should be minimal. Standardised test methods evaluate the cytotoxicity and function of face coverings and materials (ISO10993-5:2009, In-vitro cytotoxicity tests for medical devices and ISO 16900-7:2020, Respiratory protective devices and methods for test and testing equipment) [Petrachi et al., 2021 and Mier et al.,2022]. 

 

In nano-finished face masks, the outer layer is a nano-finished fabric, while the middle and inner layers are not finished. The masks with thermal elements should be placed in the middle layer, which may penetrate the outer layer under prolonged use or high temperatures, potentially increasing nanoparticle release. However, the inner layer remains unaffected, mitigating the risk of direct contact with the human respiratory system. This explanation is offered in page 11, lines 32-328.

 

• Petrachi, T., Ganzerli, F., Cuoghi, A., Ferrari, A., Resca, E., Bergamini, V., Accorsi, L., Burini, F., Pasini, D., Arnaud, G. F., Piccini, M., Aldrovandi, L., Mari, G., Tomasi, A., Rovati, L., Dominici, M., & Veronesi, E. (2021). Assessing Biocompatibility of Face Mask Materials during COVID-19 Pandemic by a Rapid Multi-Assays Strategy. International Journal of Environmental Research and Public Health, 18(10), 5387. https://doi.org/10.3390/ijerph18105387
• Meier, P. et al. (2022) ‘Evaluation of fiber and debris release from protective COVID-19 mask textiles and in vitro acute cytotoxicity effects’, Environment International, 167, p. 107364. https://doi.org/10.1016/j.envint.2022.107364on

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The article entitled 'Next generation self-sanitising face coverings: nanomaterials and smart thermo-regulation systems' may constitute a much-needed review of existing materials and technologies for creating protective masks. However, I have some reservations about the structure and content of this article.

In my opinion, the introduction should be improved first of all. The same information appears in various places in the introduction text. Moreover, it is not clear from the introduction that the reader is dealing with a review article. Among other things, the authors assured that they are investigating how nanomaterials interact with microorganisms, but there is no description of this research in the text.

Similarly, it is difficult to find out how to connect individual layers of masks in which there is electronic control of heating elements, so that a working mask is created and does not pose a risk of, for example, burning its user.

There is no information at what temperature the pathogen protein denatures. There is also no clear division of materials that can be cleaned by washing or UV-C radiation or by heating. There is also no information on the length of use of the described masks.

Author Response

Reviewer 3

We are grateful to the suggestions and comments provided by reviewers which has enhanced the quality of the manuscript. In the following sections, the authors have provided the detailed response, and the text is included in the manuscript with a different font colour.

1. Among other things, the authors assured that they are investigating how nanomaterials interact with microorganisms, but there is no description of this research in the text.

In section 3.5, self-sanitisation test for nano-finished facemasks, provides a detailed analysis of how test methods to evaluate the filtration efficiency and anti-bacterial efficacy is enhanced preventing contamination. In addition, Table 7. Nanomaterials finished on different textile fabrics tested with different virus environments provides information of how different nanomaterials can be effective against various microbes and viruses.

Since the above is already included in the manuscript, no further text has been included.

2. Similarly, it is difficult to find out how to connect individual layers of masks in which there is electronic control of heating elements so that a working mask is created and does not pose a risk of, for example, burning its user.

As noted in page 20, Section 3.4, specifically in lines 575-584, challenges of incorporating heating elements without posing a risk to the wearer has been provided in greater length.

Since the above is already included in the manuscript, no further text has been included.

3. There is no information at what temperature the pathogen protein denatures.

This point is addressed in page 16, Section 3.2, specifically in lines 496-501, where the relevant details are provided - process involves heating the mask at around 70°C for a certain period, usually between 30 minutes to an hour. This temperature is sufficient to deactivate most viruses and bacteria without damaging the structural integrity of the mask.

Since the above is already included in the manuscript, no further text has been included.

4. There is also no clear division of materials that can be cleaned by washing UV-C radiation or by heating.

Cotton, polyester, and nylon-based fabrics are durable materials that can withstand washing, drying and heating. Polypropylene, commonly used in surgical masks and N95 respirators, can be effectively disinfected using UV-C radiation without degradation and maintains filtration efficiency for short durations at temperatures of 70–80°C.

The above text has been added in page 16 section 3.1 lines 475 -479

5. There is also no information on the length of use of the described masks.

Including electronic components for thermoregulation in a textile-based product is a challenge for safety, durability, and the ability to withstand repeated use (50-100 cycles of wash), especially under different environmental conditions and after multiple sanitation cycles. Depending on the embedded electronics circuits and material quality, the lifecycle can vary from six to twelve months with proper maintenance.

The above text has been added in page 23 section 4, lines 668-671

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have adequately addressed all peer review comments and made appropriate revisions to the manuscript. The paper is now suitable for publication in its current form

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have revised the manuscript according to most of the comments. Some contents were well rearranged, and the images in the new version are much clear than the old one.

Reviewer 3 Report

Comments and Suggestions for Authors

I thank the Authors for making changes to the article, in accordance with my suggestions. The article, in the corrected version, is readable and really good. I also ask for correction of small typos (e.g. line 41 is 'self-sanitizing', and should be 'self-sanitizing').