Viruses are one of the most basic microorganisms without any complicated cellular machinery. They are made up of just a protein coat (whose structures are varied), a capsid that encloses the genetic material AND the genetic material itself (DNA OR RNA). Besides this there is no other cellular machinery like cytoplasm, biochemical constituents or macromolecules or reactions taking place.
Unlike bacteria and other microorganisms, viruses cannot subsist of their own. They need a living host cell to thrive and multiply. Every virus has an appropriate host or set of living hosts to thrive.
Considering these facts, an agent that is antiviral has to either arrest their further mobility OR render them non-functional. Virucidal agents go one step further destroy the virus completely.
Of the different agents against viruses, use of Silver in different forms has formed a subject of extensive research. Though their use has been documented since early ages, they have gathered a lot of interest in the last few decades. With the advent of nanotechnology in recent times, Silver nanoparticles have been studied a lot in regard to their action against viruses and there seems to be a good promise in this regard.
“Recent studies have identified the broad-spectrum antiviral properties of silver nanoparticles (AgNPs) against respiratory pathogens, such as adenovirus, parainfluenza, and influenza. AgNPs achieve this by attaching to viral glycoproteins, blocking entry into the host cell” mentioned by Morris et. al. (2019).
A thin silver foil or vark or varak has been used to decorate south Asian sweets and some other traditional food products. The use of silver originated in ancient India’s Ayurvedic practice of utilizing precious metals as medicinal ingredient. Historically, silver has been known as an antimicrobial astringent owing to the oligodynamic effect.
Why is Silver used as an Antimicrobial Agent?
In spite of being used for centuries, the real benefits of silver were known much later. Silver oxidizes to release silver ions that kill pathogens. It also inhibits the process of chemical bonding of bacteria cells. The small particles of silver are more effective than larger particles as they release more ions. The reason why silver and silver nanoparticles took the world by storm in preventing from pathogens is due to extremely potent attack on microbes yet low toxicity on human beings. This premise resolved several microbial issues with manufacturers in many industries. Silver is also a good conductor of heat and electricity. Due to these characteristics, it is also an excellent choice in electrical equipment, solar panels, etc.
Historical Use of Silver
In ancient times silver was used to preserve water through the use of silver vessels and coins. The medicinal use mentioned is as early as 750 AD. The therapeutic value of silver was discovered in the 17th century. It was used in the treatment of Epilepsy and Cholera. In the late 19th century and earlier 20th century, it was used for eye drops and internal antisepsis, respectively.
As a significant milestone in 1920, the US Food and Drug Administration (FDA) approved charged silver solutions as antibacterial agents. Almost simultaneously, eye drops containing silver nitrate were replaced by a silver product Argyrol for local application to prevent eye infections. The use of silver was followed in burn wound treatments in 1965. It was later in the second half of the 20th century silver started finding application as a disinfectant in food and commercial industry.
Where is Silver Used as Antimicrobial Agent?
More recently, the use of silver and its nanoparticles have been growing at a rapid rate. Today, the scenario is that you use a lot of products in your daily life that has silver particles in it. It is just that a lot of people are not yet aware of the massive range of use of Silver and its nanoparticles. The various characteristics of Silver and ease of integration with other materials make it a beneficial antimicrobial agent across multiple fields. To be specific, Silver nanoparticles are the new technology driving the rapid increase in the use of silver. Silver nanoparticles are displaying the highest rate of commercialization among all nanoparticles in the market and account for 55.4 percent of the total demand of nano-material based consumer products. Here is a list of a few areas where Silver and its nanoparticles are in use extensively.
Silver has long been present in the medical field. Some of the applications have changed or become advanced with time. Currently, Silver is used in antiseptics, wound dressings, surgical masks, hospital furniture, fabrics, glass, and beds. Silver coatings on endotracheal tubes help protect against the attack of microbes and reduce the risk of ventilator-induced pneumonia. Silver powder coatings that use ionic technology are used widely on various surfaces in hospitals to reduce the risk of Healthcare-Associated Infection (HCAI).
If you look around, there is a lot of Silver in your daily life, which you don’t see. It is so because Silver in many forms is in use in a range of everyday consumer products. Some of the products with Silver are fabric conditioners, kitchen cutting boards, baby bottles, food storage containers, bed mattress, pillow, tableware, disposable curtains, blinds, bathroom products, toilet seats, ice trays, etc. Silver is also present in deodorants, toothpaste, toothbrushes, electric shavers, tissue paper. Even your pet care products have silver content, which includes pet shampoos, litter pans, feeders, pet shelters, bedding, etc. A range of electronic products like computer keyboards, remote control, ATM buttons, vacuum cleaner washing machines, refrigerators, kitchen gadgets, etc. have silver content in them.
Clothing and Fabrics
Silver is used in baby clothes, socks, footwear, underwear, bath towels, sleeping bags, pillows, bed linens, quilts, and mattress protectors. Various silver technologies have found application in the textile industry to produce different types of antimicrobial fabric. Silvadur, Silpure, and Silver fiber involve the use of silver particles to protect the cloth from the growth of microbes that cause material degeneration or odor. These silver nanoparticles do not go away from the material even after multiple washes and keep protecting the fabric.
Food industries suffer from the risks of wastage of spoiled food and the spread of foodborne disease. Silver nanoparticles are used extensively in packaging as it inhibits the growth of microorganisms, improves quality, and increases the shelf life of food products. The most significant factor in the use of the Silver-based antimicrobial agent in the food and packaging industry is that in comparison to other metals, Silver is the least toxic to animals and human beings. Silver features in the category of ‘Generally Recognized As Safe (GRAS)’ category by the US Food and Drug Administration. It is also used in nanobiotic poultry production.
Silver particles are integrated into a range of construction industry applications like air conditioning, wall paints, antimicrobial flooring, shelving systems, decorative wood laminates, PVC wall cladding, metal suspended ceiling systems, electrical wiring accessories, hygiene laminated surfaces, carpets, wallpaper, seals, powder coating hospital doors, etc.
Silver has been known as a disinfectant for centuries. Today, Silver is used in industrial disinfectants, pool disinfectants, aquaculture disinfectants, and agricultural disinfectants. Chlorination of drinking water might lead to the production of harmful compounds. As a result, Silver is being considered now as a substitute of chlorine for water purification. NASA shuttles and Mir space station have used it for their water recycling system. Also, Silver is being used in faucet-mounted and pitcher purification systems in the USA.
How Does Silver Work?
Since ages, Silver was known to have many beneficial characteristics. But how does silver work? Scientists and Researchers gave conducted various experiments and studies to study the mechanism behind the antimicrobial activity and other benefits related to Silver. The primary tool is related to the release of active silver ions, which leads to antimicrobial effects. The silver ions enter the bacteria cell, attack, and cause instant cell death through a range of mechanisms.
(i) Protein Inactivation
Silver is believed to bind with the thiol group in enzymes and cause the enzymes to deactivate. Through a series of chemical processes, it ultimately leads to protein inactivation, causing cell death.
(ii) DNA Association
It has not been proved yet, but studies indicate that the mechanism of Silver might be related to their ability to break the hydrogen bonding and denatures the DNA molecule.
(iii) Entering the Cell
There are a lot of activities to believe that what silver ions enter the cell to destroy the growth of microbes. Specific silver transporters are not required as silver ions can make use of transmembrane proteins present to be transported inside the cell.
(iv) Ionized Silver
Silver has antimicrobial effects only when in its ionized form. Silver and all its compounds can be considered sources of active silver ions as Silver produces ions as and when it comes in contact with moisture.
(v) Effects of Silver Exposure
The results of silver exposure are the condensation of DNA in the center of the cell, leaking of cytoplasm, which ultimately leads to dehydration and cell shrinkage.
(vi) Gram-positive Vs. Gram-negative
It is a useful property of Silver that it affects gram-negative bacteria more than gram-positive ones. Due to this, silver ions contribute to antibiotic activity against gram-negative bacteria. The simple reason behind this mechanism is that the walls of gram-positive bacteria are thicker in comparison to gram-negative ones. Hence they are more susceptible to silver ions.
(vii) Silver Sulfadiazine
Silver sulfadiazine cream is a topical treatment for burn wounds. The mechanism of Silver Sulfadiazine is the slow release of silver ions, which is beneficial for the injury in contrast to other silver salts like silver nitrate. Further, large amounts of sulfadiazine do not get to the wound.
What Are the Different Forms of Silver that are Active Antimicrobial Agents?
Silver as an antimicrobial agent is available in the market as dispersion liquid and powder to be used by the various fields. Silver and its multiple forms are active antimicrobial agents. The different types are:
Silver salts like silver nitrate can provide a large number of silver ions at the same time. So a combination of silver salts with Sulphur containing compounds is proposed to enable a more controlled outcome. What we need is a stable source of a moderate amount of silver ions.
Silver zeolite s commonly used as antibacterial Silver. Many kinds of toothpaste contain silver zeolite, and the fact that Silver has low toxicity, many studies feel silver zeolite is perfect for dental materials, even periodontal pockets.
Silver nanoparticles are the most widely used as antimicrobial agents due to their capacity to be highly effective against microbes and simple synthesis process. Some facts about the effectiveness of silver nanoparticles are:
· Smaller silver nanoparticles are more antimicrobial effectiveness than the more significant silver nanoparticles.
· Nanoparticle, with more facets or dimensions, is more effective than those that have fewer sides.
It should be noted that all silver nanoparticles are toxic to bacteria, but the intensity of effect increases with the decrease in the size of the nanoparticle. Research conducted claims that silver nanoparticles of size below 10nm are found to be highly effective with the size 5nm silver nanoparticle most effective. Also, the increase in the number of nanoparticle dimensions increases the surface contact area between the nanoparticles and bacteria. This results in a more significant killing by the contact mechanism of the silver ions. Silver nanoparticles of spherical shape are the most preferred for practical applications, followed by truncated-triangular shaped nanoparticles.
Research further suggests the efficiency of small silver nanoparticles due to its size, shape, and the qualities of silver cause maximum damage to microbes. Hence, it is the most suitable antimicrobial technology for not only water disinfectants, but also as antimicrobial nano-coating on surgical instruments, devices, and wound healing bandages, as well as a range of commercial and industrial applications.
What Are the Risks Associated with Using Silver as an Antimicrobial Agent?
Yes, Silver has terrific antimicrobial properties and is used for a range of applications to fight infections and diseases. Few risks associated with the use of Silver as an antimicrobial agent are as follows:
· Cleaning products containing silver particles that end up in the wastewater can affect the environment. The silver nanoparticles can enter the ecological system. Apart from cleaning products, it holds for disposable tools, cleaning detergents, and disinfectant wipes.
· Excess use of antibiotics has resulted in interference with the resistance towards them. Researchers are worried that as is the case of medicines, the overuse of Silver might lead to bacterial resistance towards it.
· Again Silver used in industrial cleaning of water might run the risk of release of a large number of silver particles in the environment if not done correctly.
· Overuse of food containers that have Silver in it in the food and therapeutic industry might cause side effects of overexposure or a leakage.
Safe Use of Silver as an Antimicrobial Agent
There are numerous benefits of the antimicrobial property of Silver. So, humans must learn how to use it safely without causing the side effects of bacterial resistance to Silver and disturbing the ecosystem. Thus, the fair use of Silver is what should be the aim, that too, with all precautions taken. Instead of irresponsibly releasing large amounts of silver nanoparticles through wastewater, a better alternative should be chosen where less number is issued. There is also a need to use fixed silver surfaces instead of continuously disposing of silver nanoparticles in the ecological system.
Overuse of Silver should be avoided to counter the effects of the development of bacterial resistance towards Silver. It should not be used if not necessary that leads to a haphazard release of silver nanoparticles, especially in domestic use. Even in the case of industrial use, precautions should be taken for minimizing environmental release when used in water filtration units in industries.
In some cases, the technology of silver nanoparticles is of immense use. The truth is Silver plays a significant part in the sterility of the food and therapeutic industry, so there is no need to do away with it. Instead, proper care must be taken to ensure that the Silver does not leach into the products.
Market Trends for Silver as Antimicrobial Agent
According to the Silver-based Antimicrobial Agent Market Report 2019, the market figures for 2018 is $1080.9 million and estimated to grow to $1967.5 million with a CAGR of 6.2 percent. Currently market is driven by a growing demand for clinical and medical fields. Also, the rise of polymer, plastic industry, and the induction of silver nanoparticles in it are creating huge demand. Another growth sector is personal care products with the increased use of silver particles in the products, such as toothbrushes, shavers, etc.
The Silver-based antimicrobial agent market is divided into different segments depending upon carriers, applications, and regions. Depending on carriers, the market is divided into 5 product types.
· Silicate Carriers
· Titanium Dioxide Carriers
· Phosphate Carriers
· Glass Carriers
· Other Carriers
Now, based on the area of applications, the market is subdivided into different segments. The major market segments by applications are:
· Cosmetic and Medical
· Other Application Areas
According to the report, the top players in the market for silver-based antimicrobial agents are:
· Ishizuka Glass Group
· Pure Bioscience
· Sinanen Zeomic
· Koa Glass
The above companies deal with different carriers. For example, Sciessent and BASF are top producers of silicate carrier types, while Addmaster produces titanium dioxide carrier types. Milliken, Toagosei, and Nafur are top names in phosphate carrier types. Sanitized and Ishizuka Glass Group are top producers of glass carrier type.
As far as the region is concerned, the Silver-based Antimicrobial Agent Market has five segments.
· Asia Pacific
· North America
· South America
· Middle East
Among all the five regions, Asia Pacific is the biggest market at present for Silver-based antimicrobial agent products. In contrast, Europe is forecasted to witness the highest growth in the coming years. Other regions are expected to show stable growth in the coming years.
The prices of Silver-based antimicrobial agents are comparatively high than other antimicrobials. However, the prices have shown decline due to market competition, economic conditions, and the influence of raw materials. According to data collected, the cost of silver-based antimicrobial agents has shown a steady decline each year from $55.9 per kg in 2012 to $51.9 per kg in 2016. The prices are expected to dip further in the coming years. Also, the gap in the rates of different brands will likely keep narrow down.
Future of Silver as an Antimicrobial Agent
The silver-based antimicrobial agents have shown tremendous bactericidal activity. So, there is a huge requirement for these products. But, Silver is expensive, and so the Silver-based antimicrobial agents have a high price. The high price is a significant hindrance to its market expansion. However, prices have shown a decline. If the prices continue to decline, there is a possibility that Silver-based antimicrobial agents might be able to replace the cheap fungicides, owing to its efficiency.
Silver is used extensively in medical, industrial, consumer, and agricultural applications. Silver has become our new hope as a useful antimicrobial agent. So, a path of moderation and responsible use should be followed to enjoy the benefits without overdoing things. The future of silver and silver nanoparticles lies in the judicious application of the technology coupled with responsible use.
Declaimer: The Food and Drug Administration and the Federal Trade Commission has issued a warning to several companies that were claiming that silver could offer treatment against virus infections including coronavirus. This article has been written for spreading awareness on natural products and does not offer or support any claims out of silver metal.
Initially published at: https://www.linkedin.com/pulse/remarkable-antimicrobial-effects-nanosilver-atul-tiwari-phd-frsc/
- Morris D., et. al., Antiviral and Immunomodulatory Activity of Silver Nanoparticles in Experimental RSV Infection. – PubMed – NCBI https://www.ncbi.nlm.nih.gov/pubmed/31398832