Recent breakthroughs in nanostructured antiviral coating and filtration materials: a brief review

COVID-19 persists as the most challenging pandemic of the 21st century with a high rate of transmission. The main pathway of SARS-CoV-2 transmission is aerosol-mediated infection transfer through virus-laden droplets that are expelled by infected people, whereas indirect transmission occurs when contact is made with a contaminated surface. This mini review delivers an overview of the current state of knowledge, research directions, and applications by examining the most recent developments in antiviral surface coatings and filters and analyzing their efficiencies. Reusable masks and other personal protective devices with antiviral properties and self-decontamination could be valuable tools in the fight against viral spread. Moreover, antiviral surface coatings that repel pathogens by preventing adhesion or neutralize pathogens with self-sanitizing ability are assumed to be the most desirable for terminating indirect transmission of viruses. Although many nanomaterials have shown high antiviral capacities, additional research is unquestionably required to develop next-generation antiviral agents with unique characteristics to face future viral outbreaks.


Introduction
Coronavirus disease 2019 (COVID- 19) persists as the most challenging pandemic of the 21 st century, and, with its high rate of reproduction and transmission, it has caused 258 830 438 conrmed cases and more than 5 million deaths (as of November 24, 2021). 1,2 Moreover, new virus strains have evolved because of mutations, and these are resistant to vaccines that target the original strain, or they have increased the virulence of the virus. 3 Materials scientists have been working to nd ways to prevent the virus from spreading in this dire situation, even in the absence of specic vaccines, therapeutics, or antimicrobial agents. 4 The rst line of defense when it comes to battling outbreaks and pandemics is to reduce viral propagation, but the COVID-19 pandemic reveals how difficult this is on a global scale. 5 Studies show that the main pathway of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission is aerosol-mediated infection transfer through virus-laden droplets (that may be smaller or larger than 50 nm in size) that are expelled via coughing or sneezing by infected people. 6,7 Indirect contact transmission occurs when a susceptible host encounters a contaminated surface in public places such as hospitals, long-term care facilities, schools, public transportation, or businesses. 8,9 Depending on virus characteristics and environmental conditions, contagious viruses such as SARS-CoV-2, respiratory syncytial virus (RSV), rhinovirus, and inuenza can survive for days to weeks, posing a great risk for transmission. 10,11 Moreover, it has been revealed that the characteristics of a surface play a major role in the transmission of many viruses. 12 The duration in which a virus can persist on a surface is determined by a variety of aspects, including but not limited to the type of surface, type of virus strain, temperature, room ventilation, relative humidity, and exposure to light. 13 The main factors contributing to surface properties are adsorption, 14,15 porosity, 16,17 and surface hydrophobicity. 18,19 The development of efficient antiviral materials may need to be specically customized according to each type of virus because their individual methods of interacting with a surface are unique. All these factors in combination should be taken into account when designing an antiviral material. Having well-dened shapes and dimensions at the nanoscale, viruses could be considered as a nanomaterial themselves. 20 For instance, under a scanning electron microscope, the SARS-CoV-2 resembles a crown with a size of 60 to 140 nm and a height of 10 nm, which is smaller than the height of SARS (15 nm) and Middle East Respiratory Syndrome (MERS) (18.5 nm). 6 Creating smart nanostructures on the same scale and with geometry that is similar to that of viruses can be used to foster interactions that can inhibit or inactivate virus replication. 21 Additionally, many viruses utilize glycoproteins on their surface to attach to the host cell's molecules, and antivirals based on nanomaterials that resemble these cellular attachment points can be developed. 22 In this regard, recently published works show a growing interest in employing nanomaterials to ght viruses, outside and inside the host. For example, several nanoscale platforms were determined to be effective in preclinical investigations against a variety of viral infections, namely, HIV, human papilloma virus, herpes simplex, and respiratory viruses. 23 In the past year, there has been a signicant increase in the number of publications on 'antiviral nanomaterials' (Fig. 1). The present review provides a summary of the current state of research toward antiviral lters and antiviral surface coatings that could be applied for suppressing the evolution of viral pandemics as well as the challenges and drawbacks that require solutions.

Nanostructured antiviral filters
Filter-based protective devices are in high demand because they are efficient and easily utilized approaches for capturing airborne viruses. Coating or chemically modifying of lters are methods of enhancing their antiviral properties. It is also crucial, especially during pandemics, to produce environmentally friendly and cost-effective materials to eliminate shortages and to enable facile disposal or recycling methods.
More than 30 heavy metals are capable of interacting with microorganisms, and some possess anti-infective properties. 24 Metal-binding/interaction mechanisms with viruses have been extensively used in the design and fabrication of antiviral lters and viral inhibitors. 25 Copper targets the viral genome, specically the genes that are required for viral infectivity. 8 Many studies have incorporated Cu nanoparticles (NPs) as the antiviral agent upon surface modication of cellulose, polypropylene, polyethyleneimine, polyaniline, or nylon nonwovens and used to manufacture disposable surgical masks.
For instance, CuI-capped Hibiscus rosa-sinensis L. ower extract (CuI-FE) containing a pentanoic acid and 2-(aminooxy) nanocomposite (NC) coated on cotton fabric shows high tensile strength and elongation (TS 31.58 MPa and EAB 21%, respectively) with the ability to interact with COVID-19 protease (binding energy À80.34 kcal mol À1 ). 26 Aerosol droplets become entrapped and inactivated, and the efficiency of the face mask material was enhanced by assembling the mask barrier in three layers such that the outer two layers contained CuS NPs coated and impregnated onto 20D spandex, 70D nylon, and 75D polyester bers that are organized in supercoiled and vertical orientations (Fig. 2). Small, aerosolized droplets are efficiently trapped, and inactivated in the middle layer by damaging the viral envelope. 27 Furthermore, Cu deposited on a polypropylene polymer surface showed high ltration efficiency with improved adhesion when the polymer surface was treated with an oxygen ion beam, thereby forming Cu-O linkages with the Cu lm that increased its capability to reduce SARS-CoV-2 nucleocapsid expression by 75%. 28 Cuzeolitic imidazolate framework-8 nanowires (Cu@ZIF-8 NWs) were developed by Kumar et al. with the aid of pluronic block copolymer, which acts as a stabilizing agent as well as a surface passivating agent with outstanding biocompatibility and reduced toxicity. 29 Microbes are efficiently inactivated by simultaneous and sustained release of Cu and Zn ions. Additionally, the NC exhibited a lower cytotoxicity and decreased the production of pro-inammatory cytokines and reactive oxygen species (ROS) compared to plain CuNWs, along with high thermal and chemical stability, and biocidal and selfsanitizing properties. Recent studies indicate promising results for virus removal and retention with CuNP-modied surfaces by means of electrostatic adsorption forces, with great potential for application in water purication. [30][31][32] It is worth noting here that the dissolution of heavy metals in drinking water during ltration must remain within the safe limits recommended by the World Health Organization (WHO). 33 AgNPs are in high demand due to their rapid and efficient antiviral action against a broad spectrum of viruses, including respiratory syncytial virus, norovirus, inuenza virus, herpesvirus, hepatitis B virus, and human immunodeciency virus. 34 Moreover, AgNPs have also been used as a virucidal agent against the coronaviruses SARS-CoV-1, SARS-CoV-2, 35 and human coronavirus HCoV-OC43. 36 Thus, AgNPs are widely applied in personal protective equipment (PPE) development by incorporation with non-woven bers.
Viral particles with smaller diameters, such as the inuenza virus (approximately 100 nm), can penetrate through highefficiency particulate air (HEPA) lters because these lters only have the ability to block the passage of particles with a diameter greater than 0.3 mm. 37 To increase the ltration efficiency, tannic acid (TA), a plant-derived polyphenol with antiviral activity, was used for functionalization of HEPA lters as a cost-efficient adhesive with the capability of trapping viruses via affinity binding (Fig. 3). 38 Furthermore, AgNP-coated HEPA lters display a decreased ltration quality factor and a decreased antiviral quality factor (0.05-0.08 Pa À1 ) with  increased dust loading according to a previously established mathematical model, 39 as dust particles tend to prevent direct contact of AgNPs with viral particles, giving rise to a decrease in the antiviral activity. 40 Garcinia mangostana L. or mangosteen extract, which is a natural antimicrobial agent, and AgNPs were incorporated in a hydrophilic polyacrylonitrile (PAN)/hydrophobic polyvinylidene uoride (PVDF) matrix to enhance its antimicrobial activity against enveloped viruses and bacteria, including tuberculosis (TB). 41 These nanobrous membranes possess unique characteristics, including physical and mechanical stability (TS 3.76 AE 1.08 MPa, EAB 8.67 AE 1.99%, YM 150.02 AE 32.87 MPa), wide range of antimicrobial activity, spinnability, and processability upon upscale fabrications, and the potential to be utilized in multifaceted applications, for instance, as lters for air conditioning or outdoor spaces due to their robustness in extreme weather conditions. Palika et al. developed an antiviral membrane trap composed of Fe salts and amyloid nanobrils (AFs) obtained from b-lactoglobulin (BLG) milk protein, which showed an efficiency of more than six orders of reduction of infectivity against both enveloped and non-enveloped viruses. 3 The membrane possesses the ability of virus retention, as well as inactivation by strong interactions between positively charged iron hydroxides and negatively charged viruses. An enhanced sustainability footprint (96%) notably highlights the superiority of the membrane over conventional membranes in terms of cost, efficiency, and sustainability.
In a novel study, it was noted that Zn oligo-lactate (ZL)functionalized poly(lactic acid)/silk nanocrystals (SNC) on PZ15 fabric were benecial because the material can be used as a face covering throughout the pandemic if standard PPE should become unavailable (Fig. 4). 42 Natural muga-silk was employed to synthesize silk nanocrystals, which act as a barrier and prevent penetration and adsorption of water or moisture due to their hydrophobicity. This antiviral nanober matrix possesses excellent features including reusability and biodegradability, as well as sustainability.
Another recent study presented a nanoceutical cotton fabric lter coated with ZnO nanoowers (NFs) for potential use as a one-way valve membrane with improved breathability for controlling the spread of COVID-19 infection. 43 An antimicrobial analysis performed with Pseudomonas aeruginosa (model SARS-CoV-2 mimic) revealed enhanced antimicrobial efficacy of the product. An in-depth computational study has shown that ZnO NFs with two-dimensional petals display the ability to conne SARS-CoV-2 spike proteins. They are also able to attach to angiotensin-converting enzyme-2 (ACE-2) receptors in human lung epithelial cells, resulting in denaturation of the spike proteins, which conrms the trapping and inactivation of viruses.
Nano-TiO 2 is known to be one of the most prevalent photocatalysts due to its exceptional characteristics such as nontoxicity, chemical stability, photo-oxidation of organic compounds, long-lasting stability against photo and chemical corrosion, and resilient oxidizing power under ultraviolet (UV) light. 44 TiO 2 has recently been identied as one of the compounds with a capacity to deactivate both Gram-positive and Gram-negative bacteria, 45 and several viral species and parasites. 46 A research group in Thailand has employed hydroxyapatite (HA)-TiO 2 nanocomposite as a lter with superior antiviral activity under UV exposure. 47 According to the results of their experiment, they have proposed a reaction mechanism such that HA induces virus adsorption on the surface, and the viruses will later be decomposed by TiO 2 upon UV irradiation. Endre's team was able to develop TiO 2 nanowires that generate high amounts of ROS under UV light, resulting in numerous potential applications. 48 Carbon nanotube (CNT) lters function as a strong barrier on account of their high durability, excellent hydrophobicity, and high thermal conductivity, which prevents the proliferation of viruses, including SARS-CoV-2. Even though a CNT network consists of pore sizes smaller than viruses, it retains excellent breathability and viability. The outstanding thermal conductivity of CNTs permits hyperthermic antiviral effects, as witnessed by the rapid temperature increase to 65 C within 5 min, which offers resilient protection against viruses. The facile processability, light weight, and low cost indicate their feasibility and reusability, emphasizing the battle against the COVID-19 pandemic. 49 CNT air lters, mechanically supported by a porous polyester substrate, exhibit HEPA-like efficiency and reduced pressure drop. The ltration system depends on an electrically conductive CNT mat with the capability of simultaneous self-sanitation through resistive heating. This active CNT hybrid membrane reveals superior ltration efficiency (HEPA H13 level) following a Darcy's law-related trend in air permeability. 50 Carbon (C)-dot embedded nanoporous poly(vinylidene uoride) (PVDF) membranes, developed by Singh and the team, exhibited signicant features such as hydrophobicity, air permeability, breathability, excellent nano-ltration, and, most importantly, solar-induced self-sterilization via sunlight absorption and concomitant heat dissipation. 51 C-dot-PVDF membranes are an inexpensive, reusable, biodegradable, and self-sterilizing platform that can be applied in viral-blocking respirators and other PPE.
There has also been interest in graphene (G)-based nanomaterials for PPE development because of their distinctive properties such as antimicrobial activity, biocompatibility, biodegradability, and also their exibility when used in designing and manufacturing. 52,53 However, when G or graphene oxide (GO) are embedded into polymers, they exhibit reduced antiviral activity as compared to the pure nanomaterials. 52 This might be due to the fact that the nanoparticles are entrapped in the bers, thus, viral deactivation by direct physical interaction cannot occur, resulting in a diminished efficiency in antiviral activity.
Furthermore, many studies have incorporated various nonmetallic functional groups coated or embedded into polymers or non-woven bers, which can be used as virucidal agents. Their ltering capability is mainly applied in PPE development, 54-58 oxygen sensing, 59 air purication, 60,61 and water purication. [62][63][64] These nanocomposites show exceptional properties, such as enhanced hydrophobicity, biodegradability, breathability, non-toxicity, and bioavailability, as well as antibacterial activity (Table 1).

Nanostructured antiviral coatings
Less priority is given for the development of antiviral surfaces to prevent viral transmission due to the instant inactivation of several viruses on surfaces, incapacity of some viral species to proliferate outside the body, and lack of host cells. However, some viruses are viable on surfaces for a few hours or up to several days, and this poses a signicant risk of disease transmission via the surface route. Thus, there is an urgent need for developing low-cost sustainable technology solutions that prevent virus survival on surfaces and control disease spread. 11,66 More recently, numerous approaches have been employed to fabricate antiviral nano coatings for several applications, from mobile phone screens to air lters. 8 For example, by incorporating perhydrolase (AcT) into a polydopamine (PDA) matrix, Wang et al. created a biocatalytic composite that could be applied to a variety of surfaces. The subsequent AcT-PDA coatings drastically reduced the infectivity of a SARS-CoV-2 pseudovirus within minutes. 67 A poly(dimethyl amino methyl) styrene-co-1H,1H,2H,2H-peruorodecyl acrylate (PDP) coating on polyester fabric exhibited excellent antiviral activity against lentivirus-EGFP and satisfactory biocompatibility with NIH 3T3 broblast cells from mice. 68 The positive zeta potential value of PDP-coated textiles (+23.2 AE 0.2 mV) can electrostatically interact with negatively charged bacteria and viruses, and subsequently rupture the microbial structure, resulting in microbial inactivation. Moreover, due to its highly hydrophobic and oleophobic nature, a PDP coating repels various solutions from adhering to it and prevents the attachment of contaminants.
Another prominent water-borne spray-on coating made from polystyrene and functionalized macroCTA can completely inactivate inuenza A, SARS-CoV-2 (VIC01), and its alpha variant (B.1.1.7) by degrading viral RNA within 30 minutes. 69 The large nanoscale conformational changes in this coating take place from collapsed (<100 nm) to elongated (approximately 1000 nm) upon settling of viral droplets on the surface, facilitating efficient binding and rupturing of the viral membrane (Fig. 5). Furthermore, a covalently attached uorescent probe bound to nanoworms lower than 1500 mg m À2 offers a means to consider reapplication of the coating for attaining constant antiviral efficacy of the surface.
Kumar et al. applied a spray-coated dual-channel hybrid nanocoating of shellac/Cu NPs to a nonwoven surgical mask,  which is shown in Fig. 6. 70 The temperature of the coated mask rapidly increased to >70 C when exposed to sunlight, resulting in a high level of free radicals that disrupted the plasma membrane of nanosized virus-like particles. Both G and GO show excellent antiviral activities against SARS-CoV-2. 71 Aer 30 minutes of contact, Das Jana et al. found that copper oxide   Li et al. formulated a coating with long-term release-killing, contact-killing, and anti-adhesion properties, from chlorine dioxide (ClO 2 )-encapsulated micelles tethered with Cu NPs that were covalently clustered on micelle surfaces, enhancing the micelle stability and contact-killing ability. 73 Huang's team developed a chemical modulation layer loaded with mineral acid or Cu salt-doped polyaniline to dissolve the antiviral agents in outgoing droplets that eventually became signicantly concentrated, yielding dried or semi-dried respiratory nuclei, and causing deactivation of pathogens. 74 The degree of chemical modication of droplets is approximately 0.075 at pH of 2-3, with a modication efficiency of 19-49%. Additionally, the coating tends to change its color upon depletion of acid or metal ions, which can be easily re-doped. Although these innovations can be applied in healthcare, much work remains before they can be used as a tool for infection control.
Superior antiviral performance of Ag, such as its ability to deactivate viruses through binding with the viral envelope and surface proteins, makes it an ideal candidate to generate nanocoatings that can be used for surface decontamination. 8,75,76 For instance, Ag nanowires (NWs) that were electrospray-coated with polyacrylonitrile (PAN) bres on their surfaces showed a signicantly enhanced antiviral efficiency to 72.5 AE 1.9% in 30 minutes for bacteriophage MS2. 77 Chen et al. investigated the antiviral activity of GO/Ag nanocomposites, and they proposed coating of facemasks with GO/Ag NPs to reduce the risk of infectious disease transmission. 75 Most recently, Cox and colleagues developed a simple and inexpensive method to fabricate tea/cinnamaldehyde/Cu and tea/cinnamaldehyde/Ag hybrid nanocoatings (approximately 150 nm thickness) that spontaneously adhere to substrate material surfaces. 11 Interestingly, a nonwoven polypropylene coating containing tea/ cinnamaldehyde/copper and tea/cinnamaldehyde/silver resulted in 98.6 and 99.8% murine coronavirus deactivation, respectively.
A group of researchers synthesized a coating consisting of 26 AE 2 nm Ag NPs, 212 AE 16 nm Cu NPs and Cu particles (1.3 AE 0.2 mm) containing 51 AE 2 nm Ag NPs. 78 Rapid inactivation of SARS-CoV-2 on the Cu/Ag nanocoating was observed only aer 1 and 5 min with high volumes of Cu (65 and 78 wt%) and lower volumes of Ag (7 and 9 wt%). There have been some previous studies on air lters coated with Ag NPs and SiO 2 /Ag composites that demonstrated effective antiviral behavior without altering ltration performance. 40,79 SiO 2 /Ag composites also function as anti-viral coatings to be used as a next-generation technology to combat SARS-CoV-2. 80 Recently, researchers further improved Ag nanocluster (NC)-embedded silica to sputter-coat ber-based air lters with strong virucidal activity against RSV and inuenza virus type A (FluVA). 81 Prior to that, Balagna and colleagues demonstrated the virucidal effect of Ag NCs/SiO 2 directly sputter-coated (<200 nm with Ag 1.53 at%) on an FFP3 mask, with complete inhibition of SARS-CoV-2. 82 In another study, Wang et al. coated conductive Ag/Co 3 O 4 onto a glass ber cloth (GFC) through in situ combustion to manufacture an air cleaning device that could completely inhibit the pseudovirus of SARS-CoV-2 within a few minutes when a 0.05 A current was passed through at a decreased surface temperature (<50 C). 83 Zhong and colleagues developed AgNP/graphene laser-printed N95 respirators, which exhibited exceptional superhydrophobic and photothermal properties when combined with Ag + ion release upon microbial accumulation. Plasmonic heating increases the surface temperature above 80 C within 1 min of solar irradiation, and superhydrophobicity results in self-sterilization of the material. These features in collaboration provide enhanced fortication to ght the COVID-19 pandemic. 84 Moor and coworkers integrated fullerenes (C 70 ) and Ag onto polystyrene-block-poly-4-vinylpyridine (PS-P4VP) copolymers in order to obtain dual functionality. 85 C 70 and AgNPs synergistically target bacteriophage that increase photo-generated ROS under visible light illumination. ZnO nanorods and AgNP-modied poly(methyl methacrylate) (PMMA) were utilized as an antiviral coating by Karagoz's team. 86 The nanocomposite showed antiviral activity against both BCoV and BPIV3 viruses, along with its self-cleaning ability, reusability, and SERS-based sensing ability. Coating of PHBV18/AgNPs over PHBV3 lms decreased murine norovirus (MNV) titers by 0.86 log, while no infectious feline calicivirus (FCV) were recovered aer 24 hours. 87 Hasan and colleagues fabricated randomly oriented nanostructured topography on aluminum alloy 6063 surfaces and observed a signicant reduction (3-4 log 10 aer 24 h) of amount of viable RSV recovered in comparison to the control surfaces. 66 Furthermore, the nanostructured surfaces exhibited sufficient modulus and hardness to withstand 1000 cycles at 2000 mN load for over 30 min. It was observed that hydrophobic sintered ceramic with La 2 Mo 2 O 9 (LMO) powder decreased the rates of survival of bacteriophage Qb and bacteriophage F6 by more than 99.9%. 88 In an extension of this research, La and Mo of LMO were replaced by Ce or W, and the results suggested that a partial substitution of Ce for La increased the antiviral activity against F6. 89 Pezzotti et al. developed a solid-state virucidal bioceramic utilizing sintered Si 3 N 4 , and it exhibited enhanced antiviral capacities against H1N1, HEV71, FCV, 90 and SARS-CoV-2. 91 Upon the hydrolysis of Si 3 N 4 at the surface, reactive nitrogen species (RNS) were generated, which have antiviral properties. RNS can be metabolized by mammalian cells but are toxic to bacteria and viruses. It was observed that polypropylene-graed methacrylamide (PP-g-MAM) possesses excellent antiviral capacities against T7 bacteriophages, upon chlorination. 92 The composite demonstrated a high melting temperature (161 C), along with a breaking tensile stress of 7 MPa and breaking strain of 100%. Moreover, its reusability and rechargeability enable its use in protective textiles.
Many other studies have incorporated photoactive compounds, which generate ROS upon light exposure and are capable of high antiviral capacities of more than 5 log reductions against SARS-CoV-2, 70 T7 bacteriophages, 93-95 F2 bacteriophages, 96 feline infectious peritonitis viruses (FPV), 93 dengue-1 virus (DENV), 97 and vesicular stomatitis virus (VSV), 97 and these composites can mainly be used as coatings for personal protective clothing with excellent photostability, reusability, and washability, as well as biocompatibility. Moreover, an antiviral capacity of 2.4-2.8 logarithmic reduction value (LRV) was observed against bovine coronaviruses (BCoV), with the use of peroxotitanium acid/peroxo-modied anatase as the photocatalytic material. 98 This coating can be applied in cattle breeding environments as well as indoor spaces such as offices and hospital rooms.
Another major application of antiviral coatings is their use in the food industry (Fig. 7). This is of utter importance because consumption of foods contaminated with human enteroviruses, such as hepatitis A (HAV) and human noroviruses (NoVs), can cause severe disease. 99 Thus, the application of food-grade edible coatings has recently gained attention for controlling the safety of fresh products by functioning as a virucidal barrier and a preservative to reduce spoilage and pathogen attacks. These coatings show enhanced antioxidant capacities (Trolox equivalent antioxidant capacity of 4.5-14.1), and increased tensile strength (11)(12)(13) and elastic modulus (477-1607 MPa). 99-101

Overview
The goal of this mini review is to deliver the current state of knowledge, research directions, and applications by examining the most recent developments in antiviral surface coatings and lters and analyzing their efficiencies. Antiviral personal protective equipment, particularly face masks, have become a major industrial focus because aerosols comprising the viruses are smaller, and they are able to pass through most commercial lter masks, increasing the risk of infection. This is where nanotechnology comes in handy, as reusable masks with antimicrobial properties and easy decontamination could be a valuable tool in the ght against virus spread. The antiviral capability of face masks can be improved to reduce the risk of cross-infection or secondary infection during use or handling. Given the current challenges posed by the COVID-19 pandemic, disposable mask recycling could have a signicant impact on lowering economic and environmental costs. Recent advancements in this eld suggest that nanotechnology has the potential to fundamentally alter the structure and efficacy of current respiratory protection devices. 102 Moreover, large quantities of masks and PPE must be quickly produced during viral outbreaks, for example, using 3D printing and nanoelectrospinning for the fabrication of nanobers to compose lters. 103,104 Due to viral adhesion and colonization followed by proliferation with the formation of biolms, 105 surfaces in public places such as healthcare centers, long-term care facilities, public transportation, schools, and various businesses are easily contaminated. Traditional disinfection/cleaning methods such as spraying of ethanol (62-71%), sodium hypochlorite (0.1%), or hydrogen peroxide (0.5%) can be used to temporarily remove surface contamination. 106 However, antiviral surface coatings that repel pathogens via non-adhesion or neutralize pathogens with self-sanitizing ability would be the most desirable techniques. 106,107 Some of the key factors to consider when developing potential coating materials are low toxicity, high efficiency, ease of use, health concerns, and durability. 108 Nanomaterials such as metal oxides, GOs, and CNTs, as well as bio-nanoparticles such as chitosan, silver, copper, graphene, gold, and silicon nanoparticles, have yielded high antiviral capacities. However, additional research is unquestionably required to develop commercially realized substances.
The current COVID-19 pandemic has already generated a massive amount of new knowledge and rapidly developing technologies. It is now an open question as to what we should expect from the next, more evolved, and potentially far more deadly virus. The goal of materials scientists would be to develop next-generation antiviral agents with unique antiviral characteristics and high antiviral capacities by predicting the next step in viral evolution with the aid of recently published studies. We recognize that it is easier to speculate than to achieve, but the most recent breakthrough provides us with strong condence that the target viruses and their evolution trajectories are now much more realistic to identify. The search for additional universal antiviral materials, as well as efforts to uncover the universality of common viral receptors, should be pursued with even greater vigor. We hope that this article will aid in the development of more evolved surface coatings and lters to prevent the spread of COVID-19 and other infectious diseases as well as future outbreaks, control epidemics, and avoid highly undesirable pandemic and endemic developments.
The antimicrobial properties of many materials have been extensively studied, but there are far fewer reports on antiviral properties, which is a gap that should be addressed. Moreover, antiviral research requires the sharing of results and data, which is especially important during viral outbreaks. Finally, protective device functional integration and engineering are currently unsystematic, necessitating additional research and study.

Conflicts of interest
There are no conicts to declare.