By Dr Yashwant R Mahajan
Introduction-The coronavirus pandemic 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)has emerged in late 2019 as one of the gravest global threats, not only severally affecting thephysical, psychological and social well-being of the society, but also to global economic activity and social harmony. SARS-CoV-2 infection is predominantly transmitted by inhalation of respiratory droplets discharged when an infected person coughs, sneezes, talks and even breathe. Currently, no vaccine is altogether effective and a vaccine that protects against developing clinical illness may not defend against transmission to other persons.
Moreover, there is an acute shortage of vaccines around the world, particularly, in underdeveloped countries. In view of this, the only effective option available to us is a face mask to prevent transmission of SARS-CoV-2. The pre-eminent purpose of the mask is to reduce the emission of virus-loaded droplets by the wearer, which is particularly relevant for asymptomatic or pre-symptomatic infected wearers who may feel well;however,the wearer may be unaware of their infectiousness (depending on their viral load) to others. Moreover, Masks also help reduce inhalation of these droplets by the wearer.
In addition to the above, the face masks could also play a crucial role in combating other respiratory viruses which are also the most frequent causes of human diseases worldwide. Each year, this broad group of pathogens is responsible for a huge number of deaths and economic loss through days of sickness. There are many types of viruses that can lead to a respiratory viral infection. Some of the most common include: Bronchitis, Common cold, Croup (refers to an infection of the upper airway, which obstructs breathing and causes a characteristic barking cough), Flu, Middle East respiratory syndrome (MERS), Pneumonia, Respiratory syncytial virus, or RSV.
To date, National Institute for Occupational Safety and Health, (NIOSH) has approved N95 respirator masks as “the gold standard for respiratory protection for healthcare personnel”, (Researchers develop virus-fighting face masks, killing germs on contact). However, traditional masks, including N95s are not able to deactivate viruses on contact. The risk of contamination increases with wear time, and healthcare workers are advised to dispose of the face masks after patient exposure. This may lead to mask shortages and generate significant plastic waste. Furthermore, traditional masks including N95s are not able to deactivate viruses on contact.
Incorporation of antimicrobial agents such as antibiotic compounds, quaternary ammonium compounds, or metal/metal oxide nanoparticles into the face masks can improve their ability to protect against infection while also prolonging wear time and thus reducing plastic waste (Virucidal N95 Respirator Face Masks via Ultrathin Surface-Grafted Quaternary Ammonium Polymer Coatings). However, such materials can be harmful for the consumers because of their toxic effects on the humans (Quaternary Ammonium Compounds in Cleaning Products: Health & Safety Information for Cleaners and Supervisors;).
In vitro and in vivo studies indicate that exposure to metal or metal oxide nanoparticles could induce the production of reactive oxygen species (ROS), which is a predominant mechanism leading to toxicity (Toxicity of metal and metal oxide nanoparticles: a review). Recently, antimicrobial herbal extracts have been proposed as alternative antimicrobial materials, which are having low toxicity, high antimicrobial activity, mild environmental effects, and low cost (Masks for COVID-19). Depending on the extract and the nature of the material, their properties can include anti-inflammatory, antiviral, and/or antimicrobial effects (Natural products in drug discovery: advances and opportunities). Various herbal extracts have been used for the preparation of biodegradable masks that are claimed to be virus neutralizer and resist pathogens effectively (Potential biodegradable face mask to counter environmental impact of Covid-19). The herbal extract obtained from tulsi (Ocimum tenuiflorum), neem(A. indica) oil, ajwain (Trachyspermum ammi L.), black pepper (Piper nigrum), turmeric (Curcuma longa), gum Arabic (Acacia senegal), sandalwood (Santalumalbum), clove (Syzygium aromaticum), and saffron (Crocus sativus L.) were applied on the nonwoven nanofiber filter media to prepare biodegradable bio-based facemasks, named ‘Pavitra Pati, which is a patented invention of Metallurgical and Materials Engineering Department of The Defence Institute of Advanced Technology, Pune, India (DIAT) (Needleless electro spun phytochemicals encapsulated nanofiber based 3-ply biodegradable mask for combating COVID-19 pandemic). The masks showed properties such as antifungal, antiviral, antibacterial, biodegradable, super-hydrophobic (outer layer) and hydrophilic (inner layer) characteristics useful against COVID-19. In another work, the researchers have designed and fabricated an antiviral face mask using licorice root extract, which has displayed antimicrobial properties due to the presence of glycyrrhetinic acid (GA) and glycyrrhizin (GL) (Prospect of biobased antiviral face mask to limit the coronavirus outbreak).
In view of the above stated facts, there is a dire need to vigorously pursue innovative research and development activities to realize an effective face mask possessing biodegradability, renewability, antimicrobial attributes, breathability, cost effectiveness, abundance, ease of processing, adjustable aspect ratio and strong mechanical properties as compared to other traditional face masks.In the current Covid 19 pandemic scenario, it is essential that the face mask should be able to effectively filter nanosized particles in the range of 60–140 nm (The size of coronavirus diameter) (Filtration mechanisms and manufacturing methods of face masks: An overview).
Therefore, it is imperative to use nanofibrous structured materials because N 95 mask is unable meet this demand. Moreover, as emphasized in the above-mentioned paragraph, it is highly recommended to incorporate antimicrobial/antiviral herbal extracts into the face masks to endow self-sanitizing properties whilereducing/avoidingthe toxicity effects. Among the cornucopia of the world of herbs, curcumin (Curcuma longa L.)has been acknowledged as one of most important herbs, which is a bioactive compound of the turmeric. The broad-based antiviral effects of curcumin against different viral pathogens nominate this compound as an antiviral drug candidate to develop new antivirals from natural resources against sensitive viruses especially, by developing different curcumin derivatives. It has been proposed in the literature that an active layer of a blend of bioactive agents (Curcumin and Moringa) loaded nanofibrous fabrics-based face masks has the potential to synergistically combat the pandemic of covid 19 (Encapsulation of bioactive agent (Curcumin, Moringa) in electro spun nanofibers – Some insights into recent research trends).
Figure 1) Antimicrobial Properties of Curcumin
Moghadamtousi SZ, Kadir HA, Hassandarvish P, Tajik H, Abubakar S, Zandi K. A review on antibacterial, antiviral, and antifungal activity of curcumin. Biomed Res Int. 2014; 2014:186864. doi: 10.1155/2014/186864. Epub 2014 Apr 29. PMID: 24877064; PMCID: PMC4022204.(Printed under the permission of Creative Commons Attribution License)
Description-In the present work (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity), the researchers designed a three-layered nanofiber mask. Firstly, nanoengineered electro spun microporous membrane was prepared using biocompatible, low-cost and biodegradable polypropylene (PP) and subsequently, the membrane was deposited with a nanofiber active coating consisting of either polycaprolactone (PCL) or PCL plus antimicrobial curcumin.
As discussed earlier, curcumin was selected as an antimicrobial agent on account of its superb antiviral, antibacterial and antifungal properties. Additionally, the safety, tolerability, and nontoxicity of curcumin at high doses are also well established by human clinical trials(Therapeutic Roles of Curcumin: Lessons Learned from Clinical Trials). The typical schematic given in Figure 2 (a) depicts a three-layer facial mask filter consisting of two outer layers of conventional spun bond PP membrane. The inner layer is comprising a PP membrane coated with PCL/curcumin. Figure 2 (b) shows a typical low magnification image of the spun bond PP membrane coated with PCL or PCL/curcumin that is sandwiched between two spun bond PP membranes and Figure 2 (c) shows high magnification images of PCL nanofiber and spun bond PPmicrofibers.
Figure 2) (a) Schematic representation of the developed three-layer mask filter.
b) Low-magnification SEM image of the active layer showing the nanocoated layeron the 30 GSM spun bond PP layer. (c) High-magnification SEM image of PCLnanocoating (top) and the 30 GSM spun bond PP membrane (bottom).
“Reprinted with Permission from American Chemical Society (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity, Reshmi Chandran Rema, Amrita Salim, Rosebin Babu, et al., ACS Applied Polymer Materials, American Chemical Society, Jul 1, 2022)Copyright © 2022, American Chemical Society”
Particle filtration efficiency and breathability of three-layered mask filters:
As shown in Figure (3 a), the control, i.e., the three-layered PP membrane (PP3) alone showed 81.8 ± 1.3% filtration efficiency, which increased to 94.7 ± 1.1% with the incorporation of the nano filter layer coated for 10 min (PP/10PCL). With increasing coating time up to 20 minutes (PP/20PCL) the particle filtration efficiency (96.8 ± 0.1%) as well as its breathability (64 ± 2 Pa) further increased for a three-layered mask containing PCL coating with 20 μm thickness. As observed in this study, N95 filters showed high pressure drops (above ∼220 Pa) due to their dense fiber packing. This in turn, causes high air-flow resistance during inhalation. In contrast, nanocoated mask filters with and without curcumin incorporation exhibited a substantially reduced pressure drop (∼64 Pa), while maintaining high filtration efficiency.
After carrying out filtration experiments the entrapment of the particles that occurred within the nanofibers is confirmed as depicted in figure 3 (c and d). As indicated in Figure 3 (b), different concentrations of antimicrobial agent curcumin were introduced into PP/20PCL (Designated as PCL/1%cu, PCL/5%cu, and PCL/10%cu for 1, 5, and 10 wt. % curcumin, respectively). Interestingly, it was found the addition of curcumin with different concentrations to the PCL matrix did not in any way alter either the filtration performance or breathability of these filters. Moreover, based on experimental studies, it was observed that the filtration efficiency more or less remained constant even after continuous usage.
Figure 3. Particle filtration efficiency and breathability of three-layered mask filters with
a. different coating times in comparison with controls and (b) different percentages
b. of curcumin-loaded PCL electrospun for 20 min. (c,d) SEM images of particulatematter entrapment within the nanofilter, shown at different magnifi.
“Reprinted with Permission from American Chemical Society (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity, Reshmi Chandran Rema, Amrita Salim, Rosebin Babu, et al., ACS Applied Polymer Materials, American Chemical Society, Jul 1, 2022)Copyright © 2022, American Chemical Society”
Generally, in the case of face masks, the Figure of Merit(FoM) is considered to be an important parameter, which is the ratio of Particle Capture Efficiency/ Pressure Drop. Based on the experimental studies, it was found that in the case of nanocoated PP/20PCL mask,the FoM was ∼0.052 ±. 0005 Pa−1, which is five times greater than that of the commercial N95 filter. Its superior filter performance could be attributed to the presence small pore size and low surface density of the nanofibrous layer deposited on PP.
Bacterial and Bacteriophage (a virus surrogate) Aerosol Filtration Efficiency:
The bacterial (gram negative E. coli and gram-positive S. aureus) and bacteriophage (representative of viral strains) aerosol filtration efficiencies were analysed on PCL-nanocoated filters along with controls in a custom-made setup. In both the cases of bacterial and bacteriophage filtration, the efficiencies for PCL-nanocoated filters were found to be superior than that of three-layer PP alone. An aerosol filtration efficiency of >99.99% was realized for both the bacteria and bacteriophages (a virus surrogate).
In most of the times, during sneezing, coughing and talking the infected person discharges the aerosols that may contain virus or bacteria. All of these aerosols are water based (hydrophilic in nature). In order to filter these hydrophilic aerosols, it is important that the nano-porous membrane should be hydrophobic in nature. The studies revealed that bare PP, PPL as well as PCL nanocoating containing curcumin were hydrophobic in nature and therefore,it helped the air filter to inhibit the penetration of water-based bacterial and viral aerosols.
Bacterial and Bacteriophage Contact-Killing Efficiencies on Curcumin-Loaded Nano-filters:
The studies were conducted to evaluate the anti-bacterial (viz., E. coli and S. aureus) and anti-viral activities on spun bond PP membranes, PCL, and PCL/curcumin nanofiber-coated membranes, respectively. The experimental details are provided in the reference (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity). Figure 4 shows a bar chart representing the percentage viability (% Viability=1/contact killing efficiency) of bacteria/Bacteriophage after continuous contact with different percentages of the curcumin-loaded nanocoating at different time intervals.
As can be seen in Figure 4 (a and b), the control PP and PCL nanofiber specimens showed poor antibacterial activity against E. coli and S. aureus, respectively, whereas the curcumin containing samples exhibited effective killing capacity. In both the cases as shown in Figure 4 (a and b) with increasing amount of curcumin significant bacterial killing effect can be observed. Moreover, the time-dependent antibacterial effect of the curcumin-loaded nanocoating and controls under incubation at 37 °C can be seen in the case of E. coli as well as S. aureus bacteria. Curcumin is a powerful anti-bacterial agent and that can effectively inhibit bacterial virulence factors.
Figure 5 schematically shows the typical mechanism of killing of the bacteria by the presence of curcumin. In principle, Curcumin can inhibit bacterial virulence factors by inhibiting bacterial biofilm formation and preventing bacterial adhesion to host receptors through the bacterial quorum sensing (QS)regulation system. In addition, as a photosensitizer, curcumin acts under blue light irradiation to induce phototoxicity and inhibit bacterial growth (Antibacterial Mechanism of Curcumin: A Review).
Figure 4) Graph representing the percentage viability of bacteria after continuouscontact with different percentages of the curcumin-loaded nanocoating at different time intervals: (a) E. coli; (b) S. aureus. (c) Bacteriophage contact-killing efficiency for different percentages of curcumin loaded nanocoating at 1 h and 3 h, with PP and PCL as controls.
“Reprinted with Permission from American Chemical Society (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity, Reshmi Chandran Rema, Amrita Salim, Rosebin Babu, et al., ACS Applied Polymer Materials, American Chemical Society, Jul 1, 2022)Copyright © 2022, American Chemical Society”
Figure 5) Inhibitory effect of curcumin against the bacterial quorum sensing (QS) system. The main mechanism of curcumin in QS inhibition involve (1), destruction of the biofilm structure; (2) inhibition of bacterial swimming and clustering behaviour; (3) inhibition of the expression of biofilm promotor genes; (4) inhibition of the gene expression of QS-dependent virulence; (5) inhibition of bacterial cell growth
“Dai, C.; Lin, J.; Li, H.; Shen, Z.; Wang, Y.; Velkov, T.; Shen, J. The Natural Product Curcumin as an Antibacterial Agent: Current Achievements and Problems. Antioxidants 2022, 11, 459. https://doi.org/10.3390/antiox11030459” (Under the Creative Commons Attribution License CC BY).
Another essential requirement of the face mask is its anti-viral activity and this property is of paramount importance, particularly in view of the ongoing outbreak of covid 19 pandemic. In order to evaluate the antiviral efficacy of curcumin loaded active filter, Bacteriophage was used as a model system (Its activity was assessed by an E. coli-based stationary phageplating assay). Bacteriophages are commonly used as surrogates for human viruses, as they are similar in terms of size, shape, morphology, surface properties, mode of replication, and environmental persistence, yet are non-infectious (Optimal preparation and purification of PRD1-like bacteriophages for use in environmental fate and transport studies).
Furthermore, it is possible to complete large sample size investigations with bacteriophages, as testing is rapid and inexpensive. As shown in Figure 4 (c) no contact killing was observed in the case of control PP sample, whereas on the contrary, PCL/5% curcumin membranes displayed the expeditious and speedy annihilation of bacteriophages within 3 h, achieving ∼79% contact-killing efficiency (21%viability, Figure 7c), as evident from its significant PFU reduction. Generally, significant antiviral activity was exhibited by the curcumin loaded nanofibers.
Reusability
In order to assess the reusability and durability of the nanocoated masks PCL/10%cu membrane was subjected to continuous cycles of washing and after each washing and drying cycles its particulate filtration efficiency was analysed. Based on the results, it was found that there is no significant reduction in the particle filtration efficiency even after 30 washes as shown in Figure 6 (b).
These results validate the durability and reliability of facemask filters developed by the process of electrospinning.
Figure 6. (a) Photograph of the final product (three-layered nano mask). (b) Particle filtration efficiency of the nanocoated facemask after different cycles of particle filtration, washing, and drying.
“Reprinted with Permission from American Chemical Society (Nanofibrous Facemasks with Curcumin for Improved Bacterial/Particulate Filtration and Biocidal Activity, Reshmi Chandran Rema, Amrita Salim, Rosebin Babu, et al., ACS Applied Polymer Materials, American Chemical Society, Jul 1, 2022)Copyright © 2022, American Chemical Society”
Conclusion: The emergence of COVID 19 and many other respiratory diseases have severally affected human health, global economic activity and environmental pollution (due to dumping of used personal protective clothing waste). According to WHO guidelines, continuous use of face mask is mandatory for personal protection for restricting the spread of bacteria and virus. In view of this precarious situation, there is a dire need to develop versatile face mask filters with high filtration efficacy and superior antimicrobial activity. Moreover, it should possess negligible or no toxicity so that it will not pose any harm to human health.
To deal with this global threat, researcher from Amrita Centre for Nano-sciences &Molecular Medicine, India designed a nanotechnology-enhanced reusable three layered face mask, which comprises electro spun polycaprolactone (PCL) and curcumin as a nanocoating on a polypropylene spun bond membrane. The mask was developed by the scalable process of electrospinning. The filter possesses superb antibacterial and antiviral properties. The incorporation of curcumin into PCL nanofibers augmented their bacterial and bacteriophage (virus surrogate) contact-killing property, without impairing the filtration efficiency or breathability. Furthermore, the nano-enabled mask filter displayed good reusability and durability upto 30 washes, with no impairment in its performance attributes.
About Author
Dr. Yashwant R. Mahajan was Technical Advisor at International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI), Hyderabad, and also at ARC-I’s Centre for Knowledge Management of Nanoscience and Technology (CKMNT), Hyderabad. He obtained his Ph.D. degree in Physical Metallurgy in 1978 from Polytechnic Institute of Brooklyn, New York. Dr. Mahajan made major contributions in the areas of MMCs, advanced ceramics, and CMCs. Under his leadership, a number of ceramic- based technologies were developed and transferred to the industry. He has published more than 130+ technical papers in peer-reviewed journals and conference proceedings and holds 13 patents (including 2 US). Dr. Mahajan is a recipient of NRC Associateship of National Academy of Sciences, USA, the best metallurgist of the year award (IIM), MRSI Medal, MRSI-IISC superconductivity award, and VASVIK Medal. Dr Yashwant R Mahajan is also the Editorial Adviser to Nano Digest. Email: mahajan@nanodigest.in
