Application Fields of Silver Nanoparticles: History
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Contributor:
Angelica Luceri
,
Rachele Francese
,
David Lembo
,
Monica Ferraris
,
Cristina Balagna

New antiviral drugs and new preventive antiviral strategies are a target of intense scientific interest. Thanks to their peculiar properties, nanomaterials play an important role in this field, and, in particular, among metallic materials, silver nanoparticles were demonstrated to be effective against a wide range of viruses, in addition to having a strong antibacterial effect. Although the mechanism of antiviral action is not completely clarified, silver nanoparticles can directly act on viruses, and on their first steps of interaction with the host cell, depending on several factors, such as size, shape, functionalization and concentration. 

  • silver
  • applications
  • antiviral

1. Introduction

Silver nanoparticles are considered interesting materials for their great versatility, which allows involving them in different types of applications, from the biomedical field [1] to the electronics industry [2] and agriculture field [3]. Figure 1 represents a summary of the different synthesis methods of silver nanoparticles (AgNPs), their effects and possible fields of application.
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Figure 1. Main synthesis methods, effects and potential applications of AgNPs.
Since the antibacterial properties of silver have been known for many years, many commercial products have been developed to exploit this peculiarity, from home textiles (Microban® [4] SilverShield® [5]) to underwear (Silverskin® [6]) and antibacterial paints (Icosan Defend AG [7]). On the contrary, the most recent discovery about the antiviral activity of silver has not yet allowed the development of numerous products. Only with the recent COVID-19 pandemic have some products, such as masks or sprays for surfaces using AgNPs and other elements or technology, been put on the market to counteract the SARS-CoV-2 epidemic; for example, the FFP2 face mask (Nanosilver® [8]). However, antiviral AgNPs could be used in the development of products and devices in other fields with a high risk of viral infection. Researchers individuated and described the main potential applications of antiviral AgNPs in health and medical applications in terms of potential therapeutic use, veterinary use, applications in water treatment and air filtration systems, food packaging and textile industry purposes (Figure 2).
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Figure 2. Main potential applications of AgNPs in the virology field.
Table 1 summarizes the fields of application of antiviral AgNPs and a description of the AgNP system, indicating if it is an embryonic study at lab scale (indicated as laboratory study) or could be considered a prototype or a commercial product.
Table 1. Summary of the main applications and uses of AgNPs as antiviral agents.
Field Description of
Application		 System Tested Virus Study Level Ref.
Health sector Potential therapeutic use AgNPs IFVA (H3N2) Laboratory study [9]
Potential therapeutic use Tannic acid-modified AgNPs (TA-AgNP) HSV-2 Laboratory study [10]
Potential therapeutic use TA-AgNPs into Carbopol 974P gel HSV-1 and HSV-2 Laboratory study [11]
Potential therapeutic use TA-AgNPs HSV-2 Laboratory study [12]
Potential therapeutic use AgNPs RSV Laboratory study [13]
Potential therapeutic use AgNPs functionalized with PVP (ArgovitTM) RVFV Prototype [14]
Prevention AgNPs (ArgovitTM) SARS-CoV-2 Prototype [15]
Coating for surfaces Protective hybrid coatings with AgNPs realized by means of sol gel HIV-1, DENV, HSV-1, IFVA, CoxB3 Prototype [16]
Coating for condoms for the prevention of sexually transmitted viruses AgNP coating by immersion HIV, HSV-1, HSV-2 Prototype [17]
Surgical mask doped with AgNPs by immersion AgNPs obtained by electrochemical method and incorporating an aqueous solution IFVA (H5N1) Prototype [18]
Co-sputtered disposable mask Silver nanoclusters/silica composite coating by co-sputtering method SARS-CoV-2 Prototype [19]
Part of respiratory and surgical masks Graphene–silver nanocomposite FCoV, IBDV Prototype [20]
Veterinary sector Potential therapeutic use AgNPs synthesized by chemical reduction method IBDV Laboratory study [21]
Potential therapeutic use Biologically synthesized AgNPs PPRV Laboratory study [22]
Potential therapeutic use AgNPs RVFV Laboratory study [14]
Potential therapeutic use AgNPs CVD Laboratory study [23]
Potential therapeutic use AgNPs WSSV Laboratory study [24][25]
Potential therapeutic use AgNPs from aqueous extracts of clove NDV Laboratory study [26]
Water and air filtration systems Water treatment AgNPs produced via Lactobacillus fermentum (Biogenic Ag0) UZ1 (bacteriophage), MNV-1 Prototype [27]
Water treatment under UV radiation AgNPs via photochemical reduction of silver nitrate on Aeroxide TiO2 P25 and Anatase TiO2 MS2 (bacteriophage) Laboratory study [28]
Water treatment Fe2O3/Ag NPs coating on fiber glass MS2 (bacteriophage) Laboratory study [29]
Water treatment AgNP-doped and Ag/Cu NP-doped activated carbon by impregnation T4 (bacteriophage) Laboratory study [30]
Water treatment Magnetic hybrid colloid-AgNPs MNV, ɸX174, AdV2 Laboratory study [31]
Water treatment Colloidal and immobilized Ag nanoparticles on a glass substrate MS2 and T4 (bacteriophages) Laboratory study [32]
Air filtration PP nonwoven substrate with a layer of PA6 electrospun nanofiber, impregnated with AgNPs PDCoV Prototype [33]
Air filtration Silver nanoclusters/silica composite coating on air filter IFVA, RSV Laboratory study [34]
Air filtration Silver nanoparticle-coated silica particle IFVA, MS2 (bacteriophage) Laboratory study/Prototype [34][35][36]
Air filtration Nano-Ag0/titania-chitosan MS2 (bacteriophage) Laboratory study [37]
Food
packaging		 Packaging Polymeric film–AgNPs FCV and Murine Norovirus (MNV) Prototype [38]
Textile
industry		 Antiviral clothing AgNPs and phospholipid
vesicles in the
Viroblock/ViroFormulaTM		 FluVA, SARS-Cov 2 Commercial product [39]
Antiviral clothing Electrospun nanofibers with ZnO Nanorods and Ag NPs BCV, Bovine Parainfluenza Virus Type 3 (BPIV3) Laboratory study [15]
Disinfectant for polyester/viscose spunlace
wipes for use in surface disinfection		 AgNPs prepared by reducing agent or aqueous solution of PVA in the presence of glucose or photochemical reaction MERS-CoV Prototype [40]

2. Application in the Human Health Sector

Considering the human health applications, AgNPs could be used for the treatment and prevention of several viral diseases. Nevertheless, despite their antiviral activity being demonstrated against numerous viruses, the majority of studies refer to in vitro results and they are still far from the development of an effective therapeutic drug for humans. In Table 1, under the term “Potential therapeutic use”, only the studies that reached the first step of in vivo analysis [9][10][11][12][13][14]. The lack of evidence in vivo and the absence of clinical trials outline that the therapeutic/prophylactic field is not the main potential application of AgNPs at present. The principal obstacle is probably their possible toxicity in vivo, i.e., their potential accumulation in different body sites with long-term sequelae. Further investigations are needed to analyze these aspects and to open the way to the development of new antiviral drugs.
On the other hand, the prevention of viral infection is an important feature to be considered and the application of AgNPs in this field has reached interesting and developable results.
A commercial product called ArgovitTM demonstrated a dose-dependent reduction of RVFV infectivity [14]. The same system was recently tested against SARS-CoV-2 in humans [15]. Almanza-Reyes et al. tested the effect of mouthwash and nose rinse using ArgovitTM on a group of 231 participants, including men and women, in a range of age between 18 and 65 years old and with different occupations, divided randomly into two groups. The first group, named the experimental group, used a spray containing an AgNP solution mixed with water to gargle three times a day and do nasal lavages, while the second group, named the control group, used conventional mouthwash for a nose rinse and mouthwash. The results showed that in the experimental group, the number of SARS-CoV-2 infections was lower than in the control group. Therefore, the authors emphasized the importance of oral and nasal hygiene to a reduction of the risk of SARS-CoV-2 infection in health personnel who are exposed to patients diagnosed with COVID-19.
Additionally, since some viruses can be transmitted indirectly through contaminated surfaces, the development of self-decontaminating or antiviral surfaces is needed. Jan Hodek et al. tested in vitro protective hybrid AgNP coatings prepared by the sol-gel method against HIV-1, DENV, HSV-1, IFVA and COXB3 viruses (enveloped, non-enveloped, RNA and DNA viruses) [16]. The coatings, deposited on substrates such as glass and Poly(methyl methacrylate) (PMMA), reduced the infectivity of all of the above-mentioned viruses, with the exception of COXB3. This selective effect could be ascribable to the different composition of virus capsids and outer membranes and the consequential mechanisms of interaction between AgNPs and viruses. The authors showed that the system was endowed with virucidal activity against different enveloped viruses, thus suggesting that this hybrid coating, which was previously demonstrated to be active against some bacteria strains, has the potential to provide antimicrobial protection on surfaces and materials in healthcare settings. Another preliminary study focused attention on the application of AgNP-coated condoms for the prevention of sexually transmitted diseases [17]. Common condoms generally constitute a physical barrier to sexually transmitted diseases, but they have an intrinsic ability to inactivate some viruses, bacteria and fungi. Since AgNPs showed marked antiviral effect against HIV, HSV-1 and HSV-2 [10][11][41][42][43][44], Fayaz et al. developed AgNP-coated polyurethane condoms by immersion in an aqueous silver solution [17]. AgNP-coated condoms, with stable nanoparticles (not removed by water washes), were directly exposed to these viruses, showing a significant and time-dependent reduction of viral infectivity. AgNP-coated polyurethane condoms can directly inactivate viral particles, and could improve the protection given by common condoms as an important first-line product against sexually transmitted infections.
In the context of viral disease prevention and protection, the discussion can also be extended to the personal protective system (PPE). Recently, the spread of SARS-CoV-2, which generated the COVID-19 pandemic, increased the use of individual protective systems, as recommended by the World Health Organization (WHO). Traditional PPE systems have not had an intrinsic antiviral activity but have guaranteed good temporary protection. Many AgNP-doped or -coated masks have been commercialized with a specific antiviral effect (Nanosilver® [8]). A composite coating, consisting of silver nanoclusters in a silica matrix, was deposited via co-sputtering through a patented process on a face mask of type FFP3 [19]. The coating was able to effectively reduce, in vitro, the titer of the SARS-CoV-2 virus to zero after 1 h 30 min of incubation. Surgical masks were also doped with AgNPs by means of immersion in an aqueous solution containing nanoparticles obtained via an electrochemical method [45]. Considering the crucial role of face masks during the pandemic period, an important aspect that must be considered is the modification of their filtration performances. Indeed, different quality factors were evaluated, showing that the presence of an antiviral coating on an air filter system did not affect the filtration quality [34]. This solution demonstrated the effective inactivation of IFVA, another potential pandemic virus, suggesting a possible future application for respiratory devices and clinical textile materials.
AgNP-doped graphene oxide (GO) sheets were developed for personal protective equipment to decrease virus transmission, in particular for respirators and masks [15]. Besides its well-documented antibacterial properties [46] graphene oxide was chosen for its peculiar characteristics of high carrier mobility, large surface area and biocompatibility, which prevent agglomeration but help in the grafting of AgNPs on the graphene sheets, limiting the risk of toxicity. Both GO and AgNP-doped GO sheets, with an average AgNP size of 7.5 nm, were tested towards an enveloped virus, feline coronavirus (FCoV), which belongs to the Coronaviridae family, and a non-enveloped virus, the infectious bursal disease virus (IBDV), which belongs to Birinaviridae family. The researchers selected these two animal viruses only for their strict regulation in terms of handling as they do not provide zoonotic transmission. Both GO and AgNP-doped GO sheets inhibited the infectivity of FCoV after one hour of incubation, whereas only AgNP-doped GO sheets demonstrated antiviral efficacy towards IBDV. Despite the mechanism of action remaining to be elucidated, the authors hypothesized that the antiviral effect of GO sheets against enveloped viruses could be due to a strong physicochemical interaction between GO and the lipids of the viral envelope [47]. Regarding naked viruses, due to the absence of the lipid membrane, the same mechanism cannot occur. The antiviral activity was attributed to the AgNPs, with GO sheets improving particle distribution, preventing the formation of agglomerates and increasing antiviral Ag properties. This type of coating could be applied to face masks in order to improve the efficacy of N95 and three-layer surgical masks, whose antimicrobial effect is reduced in the presence of water or moisture.
Currently, the use of AgNPs for viral disease preventive strategies could be limited by the absence of methods to recollect the nanoparticles or to recycle and re-use the product in order to reduce waste and avoid the use of chemicals involved in the production of new systems.

3. Veterinary Applications of Silver Nanoparticles

Another potential field of AgNP application is animal health, since many viruses affect animals, causing high morbidity and mortality [48]. This has repercussions for the economy and for human life, because many sources of livelihood, such as eggs, milk, meat, fiber and other foods, are animal derivatives. To the best of our knowledge, there are only a few studies investigating the potential use of AgNPs as antiviral agents in animals. However, researchers would like to emphasize that these studies, as well as studies on antiviral AgNPs for humans, were performed in vitro, with application only hypothesized and still far from reality. As an example, AgNPs were tested against the peste des petits ruminants virus (PPRV), a virus highly contagious in small ruminants [22]. The vaccine against this virus turns out to be ineffective and insufficient to prevent contagion between animals and to avoid the serious economic losses that it causes. Khandelwal et al. demonstrated that AgNPs act by altering the entry of PPRV into the host cells in vitro at nontoxic concentration, and they suggested that the use of AgNPs can be explored as a new antiviral therapy against this virus.
The infectious bursal disease (IBDV) virus is another example of a virus affecting animals, generally on poultry farms, and one that can be transmitted through direct contact or through water or contaminated fertilizers. Pangestika et al. [21] demonstrated, in preliminary experiments, that AgNPs are also endowed with antiviral activity against this virus at concentrations of 20 ppm. Recently, attention was focused on a virus that mainly affects dogs: the canine distemper virus (CDV). Although vaccines are available, dogs are not protected for their entire life. Bogdanchikova et al. [23] tested a treatment with a solution of AgNPs (6%) and PVP (94%), in quantities depending on the dog’s weight, on dogs affected by CDV with a neurological and non-neurological infection. Other dogs were treated with traditional methods and were considered as controls. The author showed that treatment with AgNPs produced good results in the case of non-neurological infections and was not harmful to the dog, while all the control dogs died. For these reasons and considering the low cost and easy handling, the authors suggested that an AgNP and PVP solution can be used as an alternative therapeutic method against CDV.
In the last few years, the aquaculture sector has been characterized by a crisis due to the increasing number of infections by the white spot syndrome virus (WSSV), which is highly infectious and contagious for shrimps. As reported in recent reviews [24][25], several groups of researchers tested AgNPs, including the Argovit system, against WSSV and other pathogens infecting shrimps through intramuscular injection or oral administration, finding AgNPs a promising system for treatment and prevention of diseases affecting marine farms, with consequent losses in the economic field.
Recently, the World Organization for Animal Health has inserted Newcastle viral disease (NVD) in the category of most significant diseases, which can seriously affect several household and wild bird species, with consequences on poultry production. Two different groups of researchers focused on this topic, with the aim of obtaining silver nanoparticles from natural plant and alga, which are able to inhibit the NVD virus. Mehmood et al. tested in vitro and in ovo the effect of AgNPs obtained from Syzygium aromaticum [26]. The AgNPs obtained could be used as an alternative method for viral infections, in a concentration that allows the obtaining of an antiviral activity without a cytotoxicity effect.

4. Applications of Silver Nanoparticles in Water and Air Filtration Systems

4.1. Water Treatment

Water treatment in terms of purification and filtration is fundamental to making clear and potable water. The presence of viruses, such as the adenovirus, rotavirus, norovirus and hepatitis A, was documented both in surface waters and in underground sources [49][50][51][52]. Traditional procedures for water disinfection are chlorine, which led to the production of harmful disinfection byproducts in addition to bad odor or taste, and UV methods, which are not effective on some types of viruses, such as the adenovirus [53], even if they do not form byproducts [54]. An alternative approach can be represented by the use of AgNPs combined with other specific materials, creating systems with increased antiviral effect, without changing the physical and chemical properties of water and limiting the release of NPs into the surrounding environment. As an example, a study demonstrated that AgNPs, produced via L. fermentum, forming the so-called Biogenic Ag0, are able to inactivate murine norovirus-1, and suggested that the inactivation of human noroviruses could also be possible [27]. Another example is titanium dioxide (TiO2), which also has the peculiar property of being an environmentally friendly photocatalyst for water treatment. The effect of AgNPs, deposed via photochemical reduction of silver nitrate on TiO2, was verified against the bacteriophage MS2 under UV radiation [28]. The bacteriophage MS2 was used by the authors as a model due to its similarities with other waterborne viruses in terms of resistance to chlorine and UV, which is comparable to or higher than those of the hepatitis A virus [55] and poliovirus [56]. Only TiO2 inactivated the viruses in 2 min, but the addition of AgNPs to TiO2 determined an additional antiviral effect and faster inactivation kinetics. The mechanism can be explained by considering that silver promotes charge separation, causing an increase in the production of ROS, and that virus binds to newly generated HO radicals. Consequently, the adsorption of MS2 on titanium dioxide surfaces was improved, increasing the inactivation rate. The authors propose the use of nAg/TiO2 materials for the development of photoreactor or photocatalytic systems for the disinfection of water. An alternative hybrid system was developed using glass-fiber substrates coated by Fe2O3 and AgNPs (FG-Fe2O3/Ag) uniformly distributed. This system demonstrated an excellent antiviral activity against the same bacteriophage, MS2, and it could be involved in existing implants to improve disinfection effects [29].
Another material widely used in water filtration is activated carbon, thanks to its peculiar nanostructure, high porosity and large specific surface, which make it a valuable absorbent material. Activated carbon filters are not able to neutralize waterborne viruses themselves, but a Ag/CuNP-doped activated carbon filter was tested towards a bacteriophage (T4) selected as a model virus structurally comparable to enteric human viruses [30]. Considering the excellent results in the antiviral field, this filter could be considered a promising material in water purification, thanks to the synergistic performance of activated carbon and Ag or Cu NPs, which act in the interaction between the carboxyl groups of the amino acids present on the virus and the silver, causing the formation of insoluble compounds.
An additional method involved the use of micrometer-sized magnetic hybrid colloid decorated with AgNPs, considering the preservation of environmental media [31]. In fact, these particles can be easily collected after use with a simple magnet, limiting the potential risks to human health and the environment. Tests in different environmental conditions were conducted against the murine norovirus (MNV), the bacteriophage ΦX174 and the adenovirus (AdV2). The AgNP hybrid colloidal system showed an antiviral effect against the bacteriophage and MNV, depending on the AgNPs’ concentration, size and time of exposure (as already explained in the previous section), but not towards the adenovirus. Strong acidic and alkaline conditions (pH = 2 and pH = 12) reduced the antiviral activity of the AgNP hybrid colloidal system. The authors hypothesized that the adenovirus size, which ranges from 70 to 100 nm, compared to 27-33 nm for bacteriophage ΦX174 and 28–35 nm for MNV, could influence the interaction between the virus and AgNPs and, consequently, alter their antiviral activity.
This type of application has a potential huge impact on human health on a global scale, since it allows the obtaining of pure and disinfected water with systems that do not contaminate or pollute the environment.

4.2. Air Filtration Systems

Many microbial agents, such as viruses, bacteria and fungi, can remain in the air for a long time and be transmitted to a susceptible host through inhalation. Moisture in heating, ventilation and air conditioning (HVAC) systems and the accumulation of dust create a favorable environment for bacteria and fungi proliferation [57]. In addition, modern high-efficiency particulate air filters (HEPA) only limit viruses and bacteria transmission, without completely inhibiting the proliferation of bacteria and fungi or inactivating viruses present on the surface or in the filter’s porous structure. This is a potential risk for human health since a possible consequence could be poor air quality and an increase in respiratory diseases. The design of a multilayer filter with different degrees of porosity could be an efficient strategy if the nanoporous membrane is loaded with AgNPs [33]. The combination of the antimicrobial AgNP properties and the nanoporosity, derived by spun nanofibers, increases the possibility of entrapping and inactivating microorganisms with excellent air purification performance.
As reported in the previous section, an innovative composite coating, already tested towards SARS-CoV-2 on disposable masks [19], was also deposited on metallic and glass fiber air filters for antiviral activity evaluation against three airborne viruses: the rhinovirus (HRV), influenza A virus (IFVA) and respiratory syncytial virus (RSV). This patented coating, composed of a silica matrix embedding silver nanoclusters, was deposited via co-sputtering [58]. The main advantages of this thin layer are the gradual and controlled silver ion release, without nanoparticle dispersion into the surrounding environment, thanks to the silica matrix; the ability to conform adaption to any material, including flexible or thermal-sensitive substrates; and the “green” co-sputtering method used for the deposition, which is easily industrially scaled-up [59][60]. Besides its verified antibacterial properties without altering filtering performance [61], the deposited coating drastically reduced RSV and IFVA titer, while no changes in the number of infective particles were visible in the case of HRV. This probably depends on the different structure of the viruses, as HRV is a more resistant naked virus and less susceptible to different conditions, such as pH or temperature, than viruses endowed with a lipid bilayer, such as RSV and IFVA.
Similarly, an air filter with AgNP-coated silica particles was studied against aerosolized bacteriophage MS2 and IFVA, considering continuous airflow conditions [35][36][62]. A schematic comparison of the two systems is represented in Figure 3.
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Figure 3. Comparison between two different silver–silica systems: (a) nanostructured silica composite coating containing silver nanoparticles; (b) silica particles decorated with silver nanoparticles.
This system had several advantages, such as the possibility of avoiding aggregation phenomena and collecting particles after use, and the efficiency of the production process without dangerous effects on human health and on the environment [35]. The increment of the areal density coated by SiO2–Ag and the AgNP amount improved the antiviral effect, as MS2 and the IFVA virus interacted directly with Ag nanoparticles of the filter. However, an increment of the deposition time of the viral particles together with the presence of deposited dust on the filter decreased the filtration quality, limiting the inactivation of the virus. In particular, dust prevents direct contact between Ag nanoparticles and viruses [36]. In fact, after 1 h of exposure to the coated Ag–SiO2 filter, 80% of the viral protein HA was damaged and 20% of the activity of the viral protein NA decreased [35].
This type of application has an important impact on everyday life: it is possible to obtain an eco-friendly system capable of monitoring and improving air quality, with great attention to the indoor environment, in order to reduce the risks of human respiratory diseases.

5. Applications of Silver Nanoparticles in the Food Industry

AgNPs are generally used in the food industry by being embedded in polymeric matrices to create films or containers for food, in order to avoid contamination with bacteria and fungi [63]. However, some viruses, such as the human norovirus (HNV), HRoV and HAV, can also be transmitted through the fecal–oral route, thus spreading through food and contaminated fomites [64]. To counteract this problem, a polymeric film of poly(3-hydroxybutyrate-co-3 mol%-3-hydroxyvalerate) (PHBV3) with an electrospun coating containing AgNPs, was developed as a food packaging application [38]. The composite Ag/polymer film demonstrated an antiviral activity, increasing proportionally with the Ag amount, towards FCV and MNV, and was used as a predictive model of human viral pathogens.
Despite these preliminary studies, the use of AgNPs in the food industry must be carefully evaluated case by case. In fact, it is necessary to evaluate any harmful effects on humans, as an accumulation of nanoparticles and the release of Ag ions can damage the liver, spleen, kidneys and lungs, but also the immune system [65][66][67].

6. Applications of Silver Nanoparticles in the Textile Industry

Beyond the recent pandemic, the main demand for antiviral textiles has always been in the healthcare field, where patients and workers are at high risk of contracting viruses [68]. Textiles generally used in hospitals and clinics or in direct contact with patients, such as fabrics for bandages and personal protective equipment (PPE), could be a vehicle for transmission of some resistant viruses. As example, a recent publication indicates that SARS-CoV-2 can persist, in the presence of a soil load, for up to 21 days on experimentally inoculated PPE, including materials from filtering facepiece respirators (N-95 and N-100 masks) and plastic visors. Other main applications for antiviral textiles involve crowded places and environments with a certain risk of cross-infection, such as public transport, kindergarten classrooms and public offices. Moreover, in the context of the COVID-19 pandemic, many textile fashion companies, in particular in Italy, decided to invest in the development of textile products with antiviral protection, along with antibacterial activity, to satisfy consumer demand and need. In particular, Albini Group, an Italian company specializing in high-end fabrics for shirts, developed a new technology called ViroFormulaTM [69], ideal for the production of shirts, jackets and trousers, but also masks, gowns and any other garment. This technology was industrialized on the basis of Viroblock technology, formulated by HeiQ, a Swiss company. Viroblock developed a system for conferring antimicrobial and antiviral properties on fabrics, exploiting the synergic action of AgNPs and phospholipid vesicles, which destroys the virus envelope by binding to the virus and preventing its replication [70]. This system was used for the production of protective masks, mattresses, pillows and nonwoven medical garments. Its effectiveness was tested against different types of influenza viruses and remained unchanged after 30 washes at 60 °C. In addition, it was tested against SARS-CoV-2, showing a reduction of 99.99% of the virus titer [70].
In general, the main procedures to confer antiviral properties on textile materials via AgNPs involve the addition of the antiviral agent directly into the polymer solution during the spinning process or through a finishing method as the impregnation of the final product. Multifunctional poly(methylmethacrylate) nanofibers with ZnO nanorods and AgNPs demonstrated antiviral activity against the bovine coronavirus (BCV) and bovine parainfluenzavirus (BPIV3) [71]. The solution containing the polymer ZnO obtained via hydrothermal technique and AgNPs prepared via AgNO3 reduction was directly electrospun on mats for producing protective clothing. Another study verified the antiviral performance of AgNPs sprayed on polyester/viscose spunlace wipes for use in surface disinfection [40]. The AgNPs were prepared by means of different processes using reducing agents, such as trisodium citrate with cotton yarn; through an aqueous solution of PVA in the presence of glucose; or via photochemical reaction of polyacrylic acid and silver nitrate solution. All of the proposed methods allowed a good distribution and stability of the nanoparticles, but only the fabric doped with AgNPs obtained using cotton as a reducing agent and from the photochemical reaction process showed an antiviral activity towards MERS-CoV.

This entry is adapted from the peer-reviewed paper 10.3390/microorganisms11030629

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