Antimicrobial ProtectionAntimicrobial Textiles:Since the beginning of times, the human organism had to rely only on certain blood components to resist disease invasion, without knowing the mechanisms involved. In the mid 19th century, the world discovered the existence of micro-organisms. Protection against infection then became a science known as immunology. Since the discovery of micro-organisms, the skin, the largest human organ, was no longer the only barrier against infectious agents as textile products became an indispensable ally in the war against pathogens. The medical community’s initial preoccupation was limited to wound healing and infection treatment. With the evolution of the microbial flora and population growth, the need for protection against pathogen agents became imperative.
Textile products have developed to a point where they can provide a complete barrier to microbiologic agents (MA). Today the expectation goes beyond the barrier; the world now wants biocide fabrics to prevent transmission or propagation. Protective garments or even underwear such as Releaf™ is the future roundup for bacteria, the viral guillotine. • Coatings - paint • Cosmetic products • Plastics • Water treatment • Disinfectant • Paper, • Leather • Wood products • Textiles • Underwear For all these applications the vector for the antimicrobial activity is an aqueous or solvent base solution in which an active agent is dispersed in the solution. The treatment is either added to the formula of the product, as per the first 5 items of the above list, or by coating the products, like in the case of leather, wood products and textiles, although textiles can contain both types of treatment. It is possible to make a textile product MA resistant by surface treatment and by yarn design. In the case of undergarment such as Releaf™ the biocide treatment neither of the above, the biocide is trapped in the adhesive keeping the impermeable membrane together with the absorbent layer, thus providing a durable effect. 1. NATURAL or SYNTHETIC FIBERS At the very beginning of the Book of Genesis, we are told that the human race shall not have access to knowledge. According to the Bible, God, in his great wisdom, forbade Adam and Eve to take the fruit from the tree of knowledge. According to Biblical scholars, Eve and Adam surrendered to the temptation and tasted knowledge. They then quickly realized that they were naked; thus laying the first stone of the garment industry. Textile product manufacturing was facilitated by the diversity of fibrous substances available directly from nature. Cotton, linen, silk, corchorus or the asclepiad, although resulting in comfortable garments, the materials offered poor resistance to biological degradation and practically none against fungus proliferation. One notable exception is the Shroud of Turin which has miraculously been preserved throughout the centuries. In most cases, natural fibers return to nature and blend back into the matrix. Synthetic yarns, as innovative as they may be, are made from petroleum byproducts, which are generally more durable and less bio-degradable but still offer poor resistance to fungus growth. The following table illustrates the persistence of some bacteria on various fibers in days:
Thus textile fibers, whether they are natural or synthetic, all require the addition of a substance to be protected against microorganisms. There is, however, an exception from the mineral world. A fibre found in nature which provides an absolute resistance to degradation and biological activity is know as chrysotile. It can be woven in a textile product with amazing antibacterial characteristics. These types of fibers (others are called crocidolite and anthophyllite) are made of magnesium and silica, their generic name is asbestos, from the Greek word ασβεοτοζ meaning non flammable. In French the word is amiante also from the a Greek word amiaνtoζρ meaning incorruptible. If the goal of our quest was aimed at finding an intrinsically natural antimicrobial fiber, our journey could stop here. There is however a down side to this miracle fiber, it is listed as a toxic product by the European community. Although asbestos is fantastic for break pads and flame proof flexible barrier, the dust fiber that it emits makes it il-advised for use in clothing. 2. THREE APPROACHES TO TEXTILE Traditionally, antimicrobial formulations were introduced to textiles in order to protect the fabric itself from biological degradation. In the 80’s, antimicrobials were popularized as odour suppressants. Today, the benefits go far beyond this; we now rely on antimicrobials to eliminate MA. With this new advantage the question then becomes: where should the antibacterial be placed? In the fibre, on the fabric or in the laundering process? The textile industry decided to go with all options and leave the choice to the consumer. The first option consists of adding a substance which is harmful to MA in the fibre or in the fabric. This substance is gradually released, thus the name Diffusive Treatment. This treatment is given on the finishing line at the weaver or the dyer through an aqueous process. Metallic hybrids have become more and more popular. Instead of a treatment in an aqueous solution, metal oxides such as copper or silver are attached to the fiber, then made into a yarn which in turn will become a fabric. The third option is a Post Treatment, an additive designed to be added to the laundering water each time the product is washed. 3. DIFFUSIVE TREATMENT Most diffusive treatments need to be done by aqueous mode although there are exceptions. The effect of diffusive treatment is measured by the inhibition zone. The test consists of counting the number of millimeters around a swatch of treated fabric left in a petree dish submerged in microorganism nutrient. The larger ’’growth free zone’’ the better the treatment is rated. This is however a debatable statement as a fabric may be 100% biocide while generating very little growth free zone simply because the active agent is not diffusive, it remains within the fabric. Diffusive treatments have a tendency to fade after washing as they escape from the fabric at each laundering. A good antimicrobial fabric should resist at the very least 10 launderings @ 50 0 C. 3.1 Iodine: Iodine, part of the halogen family, was discovered by Comtois in 1811. Once dissolved in carbon tetra chloride it takes on a lovely purple color and is known as chloroform. For example, some of its isotopes help in the medical treatment of the thyroid gland. But what people understand from iodine is that it is used for wound disinfection. Triosyn Corporation developed encapsulated iodine enabling the active ingredient to be slowly released in pure biocide mode, killing the micro organism on contact. The fabrication mechanism involves the fusion, under high pressure and temperature, of iodine crystals with resin forming micro spheres held together by chemical links. It is exactly these chemical links that release iodine molecules in the presence of the microorganism; the iodine leaves the resin to move to the surface of the microbe’s protein which is more electrically charged. The iodine molecule removes the electron from the protein that becomes immediately sterile. One could call the process a chemical castration. Despite their lethal effect on microorganisms, Triosyn’s micro spheres present no risk to human health. One inconvenience is the yellowish color that it leaves to the skin or clothes. Due to its reactive nature, the resin will lose its killing power with time depending on the biological agent exposure frequency. Filtration applications are ideal for this technology. When it comes to fabric treatment, there are still challenges to overcome on the attachment to the fiber or yarn. 3.2 Cyanogens Cyanide, a simple combination of carbon and nitrogen with deadly consequence on microorganisms, and for humans for that matter. The mercury cyanide is used to make cyanhydrique acid; it takes only 0,06 g to permanently harm a person. Retroscreen has developed a combination of fibre and bromine cyanide. They call their invention viral receptor. 3.3 Quaternary Ammonium Saniguard says they can annihilate MA to 99,9% in 5 seconds on a vaporized surface. The MA’s included are bacteria, viruses and fungi. The Saniguard particularity is its non aqueous nature, it works using CFC as a vector. It can obviously be vaporized on fabric but its effects remain temporary. 3.4 Triclosan For over 25 years, the industry offered trichloro-2 hydroxyl biphenyl either to protect fabrics against fungus degradation or bacterial growth; this chemical compound is better known by its nickname Triclosane. Thompson Research commercialized this product under the name Ultra fresh. It is generally attached to the fabric by the impregnation process preferably after dyeing since Ultra fresh will not resist the elevated temperatures required for dyeing. Ultra fresh has a wide spectrum activity, it stops bacteria growth by an electro chemical action on the cellular membranes. Ciba promotes its own trichloro-2 hydroxyl biphenyl ether named Tinosan AM110 which only needs to be mixed with a dyeing solution, thus a version that can withstand higher temperatures. 3.5 Chitosan There is a natural antimicrobial agent extract from chitine that is found in the shells of shellfish. The company Vanson commercializes the compound as a fat absorbent in the form of a pill. 4. POST TREATMENT Post treatment is done at the laundering stage (after the product is made and sold). The process is intimately linked to chlorine, the ultimate antimicrobial. The chlorine’s lethal power surpasses the microbiologic world; it has been and still is a major component of many chemical weapons. It versatility also makes it inoffensive when combined to other elements such as sodium for example (table salt). Since the discovery of bacteria, chlorine has been considered a formidable neutralizing agent for microscopic agents. Virus and bacteria usually end up finding ways to adapt to numerous man made suppression modes but even with thousands of generations of mutation they were unable to do anything against chlorine. This is what Vanson Halosource based their Haloshiled on, a technology that allows chlorine to bond on cotton, nylon, polyester, Lycra and polypropylene. Haloshield is particularly interesting as it recharges by a simple wash with chlorine bleach. The recharge is necessary to compensate the chlorine’s volatility. As any good disinfectant, 99,9% killing rate is reached within an hour which is quicker than most other aqueous treatment. 4.1 Chlorine Grafting To a point following the foot steps of Vanson, a team of researchers from Auburn University and California University worked on the attachment of reactive radicals on fabrics to reach self decontamination especially for the firefighter’s turnout gear. This concept also uses recharges. 5. METALLIC HYBRIDS MINERALS Fibers (or filaments) are extruded at temperatures of approximately 200 C. The addition of organic MA at this stage is not feasible hence the interest in having substances more enduring to heat. We have already established that a certain fibrous mineral would remedy the heat resistance problem if it was not to the bad reputation associated to asbestos. But what about other minerals, even non fibrous, could they bring some antibacterial characteristics, could they be introduced in textile products? Indeed, nature has many tricks up its sleeve, copper, silver and gold happen to show good anti microorganism properties. Gold Prized metal since the beginning of times, gold chemical stability contributes to its qualification as precious metal. Used to cover wooden, stone or other metallic statues, thin golden foils provide longevity almost inalterable and only limited by abrasion. Gold coverings, dating 3000 years BC reached us through Tutankhamen’s grave; any other metal would have disappeared completely which may have led us to believe that ancient civilizations were working only with stones. Already in 1700 BC, it is possible to make thin foil of gold to adhere to a smooth surface. Today, the malleable metal can be reduced to thickness of 1 micrometer.* * One ounce of gold can produce 1000 gold 80 mm X 80 mmm foils. Sold in pack of 500 units, one pack covers a surface of 36 sq ft. Despite its exceptional stability, gold has virtually no application in textile when it comes to fighting MA. The reason is that other metals, equally or more bicoidal, are much less expensive. SILVER Silver has been known for its “purifying” properties for several millennium. The Persians among others took the precaution of serving water in silver cups for the men on military missions. Today with the development of high purity silver textile deposition methods allows significant progress in the treatment of severe burns and other persistent wounds. Not only does silver neutralize bacteriological activity, it also speeds up the healing process by providing a substitution for the skin’s electrical equilibrium. Pure silver fabrics remain an expensive item. Plasma deposition was, for the past few years, the emphasis of several research programs worldwide. The conclusion for most of these programs was that plasma technology does not provide advantages over convention textile treatment as far as performance is concerned and remains a more expensive operation. Therefore, pure silver treated fabric is now mainly made with solution impregnation of silver nanoparticles attached to the fiber’s surface by specially formulated bonding agents. The product commercialized by Noble Fiber Technology under the name Xtatic is a nylon covered with silver. Initially developed for static dissipation (thus the name), Noble turned their marketing approach towards odour abetment and biocide fabric. A 5% substitution of the regular yarn with the Xtatic is sufficient to provide a level of antimicrobial activity. The silver yarn will oxidize with time but very slowly. However extensive washing cycles will accelerate the degradation caused by oxidization despite the remaining presence of silver even after 250 washes. The key to success of the antimicrobial effect with silver is in the limitation of oxidization. In the case of Xtatic, the silver is completely integrated into the fiber as opposed to a surface treatment, oxidation is therefore negligible in the short or medium term. Notwithstanding this, silver should not be considered the ultimate microorganism protection as it does not cover the whole range of bacteria. Although very efficient against gram positive bacteria responsible for odors, silver has little effect on gram negative bacteria and little effect on most viruses. The main inconvenience in silver technology is its ineffectiveness against fungus. This proportion towards gram positive versus gram negative is favorable in today’s context where the rate of infection by gram positive bacteria has increased in recent years. They account for 64% of the nosocomial infections filed in the US compared to 27% for the gram negative (8% for fungus). Forty years ago the situation was reversed. (Edmond MB et Al. Clinic of Infection Disease 199;29:239-244.) In other cases, fabrics are treated with silver solutions where silver ions are bonded more or less permanently to the yarns of the fabric. Using this technique, it is possible to attain very high levels of purity which makes silver fabrics usable for the treatment of severe burns. DRM is a small company which specializes in custom wound dressing for patients with severe burns; in this case the silver cloth with humidity accelerates healing and skin reconstruction. Oxidization is not a preoccupation in this application for the sliver cloth is used only once. Foss shield technology also relies on silver. In this case silver is linked to two polymers acting as a hook to the fiber in addition to the buffer effect allowing slow release of silver ions. COPPER Copper is the most important metal for human physiological activity. Copper ions, in single elements or in complex molecular form, have been used for centuries for disinfection. In the 50’s copper was found (in naphtenate form) in cotton fabrics for tents and tarp to prevent fungus growth. This type of treatment remained vulnerable to water exposure as it was easily washed out by rain. Copper is also efficient against viruses. Copper is now used to purify water from all kinds of microbiologic agents. It also has beneficial skin restoration "powers"; some skin creams contain copper. Microorganisms, except for viruses, have developed several mechanisms to tolerate excesses of copper. For example: • an envelope use as a selective membrane• sequestration by cellular envelops • ion transport by metabolic precipitation Independently of the creativity deployed by the microbiological world to counter the effect of a prolonged exposure to a relatively high concentration of metal, copper remains invariably toxic for micro organisms. Despite this happy conclusion, the permanent link between an organic compound and a non organic compound remains a challenge particularly on a mass production scale. Cupron an American company with an R&D center based in Israel has succeeded in developing a method to attach chemically copper, in its oxide form, to various fibers, natural or synthetic. Not yet well known, the Cupron technology was introduced seriously only 2004. A fabric with 50% of copper yarn (which contains 3% copper oxide; provides a micro organism resistance at 99.9% . The main advantage of the copper oxide yarn is its stability to laundering and oxidization. No reduction in biological activity is noted when subjected to a caustic solution with a pH of 13, under boiling point conditions of one hour. The technology developed by Cupron offers protection against gram positive and gram negative bacteria, fungus, dust mites and mildew. It can be applied to polyester, nylon, cotton and polypropylene. 6. Alternatives All Antimicrobial treatments from the Diffusive Process are mostly done prior or during the dyeing process. These treatments are considered superficial in the sense that they are not 100% permanent due to their diffusive nature; who says diffusion says losing active agents. It is possible, however, to have a sufficient amount of active ingredients for the life time of the product. 6.1 Laminated Products In the case of the laminated product, it is possible to make a diffusive treatment almost permanent. Instead of treating the fabric, an antimicrobial agent is added in the adhesive. The active ingredient will radiate, thus creating an inhibition zone, while remaining resistant to laundering. This process becomes quite practical to overcome the difficulty in treating polyester with a diffusive treatment; because of its hermetic nature, polyester fiber is less susceptible to let a substance penetration unlike cotton or even nylon. Adhesive treatment makes it possible for polyester fabric that happens to be laminated to maintain an antimicrobial activity despite prolonged washing cycles. This fragmentary imprisonment of the Diffusive Agent suffices to resist fungus bacteria. 6.2 Micro Encapsulation One technique, although not frequently used’ consists of placing antimicrobial agents contingent in between 2 membranes. The membrane’s permeability allows the controlled release of active ingredients which migrates to the surface. This type of process is mainly attributed for products that do not get laundered like mattress covers and separation curtains which are a perfect nest for bacteria proliferation. With complementary methods, protection can last for several years. 6.3 Microbe Shield Microbe Shield from Aegis, may seem at first totally inefficient, no inhibition zone around the tested sample. We can’t judge a book by its cover as we can’t judge an antimicrobial by its inhibition zone. The Microbe Shield simply does not diffuse, it stays on the fabric and prevents bacteria development on the fabric only, not in the surrounding environment. When subjected to the patri dish test, the sample appears to be fully covered by bacteria but it is in fact the nutrient solution which is covered with bacteria. The sample has no alteration to fungus or any other microorganism activity and the sample can be cleaned with water to recover its original state. The ionic action of the Microbe Shield forces the cellular membrane to break immediately on contact with the fabric treated surface. The substance responsible for this is trimethoxy silyl propyl dimethyl octaecyl ammonium chloride. To make things easier, we can classify all the above treatment methods into two categories: the passive and active types. The passive, for those which provide a surface hostile to the development of microbiological activity and the active, for those that interact directly on the microorganism by a molecular attack (a displacement of ions). Based on this definition, we can establish that the biologically active textile is the one that can be designated biocide. A biocide fabric, in reusable applications, must provide an antimicrobial effect on a long term basis preferably without having to be retreated. Thus next time you ask for a material made with biocide fabric do not forget to ask for "how many launderings and at what temperature"? REFERENCES
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