Antimicrobial textiles are those which can inhibit the growth or kill microbes, which is the broad term for micro organisms such as bacteria, fungi, algae and viruses. This functionality was originally developed as a means of preserving textiles from perishing due to microbial attack. Natural fibres are typically more susceptible to supporting microbial growth but all fibre surfaces within a textile provide an environment for microbes to attach, and conditions such as heat, moisture and the oxygen availability within the textile structure complete the necessities for microbe multiplication.
The threat of microbial degradation of Geotextiles is a challenge of the sector as the continued exposure to moisture and bio organisms provides contact and growth conditions. This can, of course, be advantageous if biodegradability is a required quality. However, in a subsidiary protection role, the requirement to perform unimpaired long term requires microbial protection and synthetic fibres are more commonly used in this area for this reason.
In the Apparel and Sports & Leisure sectors, garments with added ‘freshness’ incorporate silver particles into the fibres or as a finish, providing microbial protection, preventing odours, staining and possible infections. Body heat and moisture provide ideal conditions for microbial activity and wicking textiles to aid fast drying can further minimise the growth risk. This kind of close-to-skin application requires antimicrobial to be biocompatible.
The largest scope for antimicrobial textiles is within the Medical & Hygiene sector, which includes a wide range of applications, from bandages and other wound management systems to bio implants and baby diapers. Textiles in hospitals are a necessity for both protection and comfort, including woven and non-woven items such as bedding, towels, uniforms, bandages and wipes. All these items can harbour potentially pathogenic microbes and provide a risk of cross-contamination, but antimicrobial properties aid to minimise this risk.
Interior textiles such as bedding, upholstery and flooring further utilise antimicrobial properties to provide products to minimise the growth of allergens such as dust mites.
Term and Definitions
The term 'antimicrobial' can be broken up into the further subheadings.
'Cidal' is defined as killing the organism, whilst 'static' means inhibiting growth through disruption of the reproduction process and, as such, terms like 'bacteriostatic' and 'fungicidal' are applied accordingly.
Basic Principles of Antimicrobial
Antimicrobials are complex and do not all work the same, however, they generally work by interfering either with a microbe’s respiration process, leading them to die (cidal activity), or disrupting the reproduction process (static activity), which inhibits multiplication and therefore growth. Different protection levels in textiles are available to meet the requirements, usually determined by the end product use.
At a cellular level, many antimicrobials are ionised, cationic elements, or mimic these properties. These cations then take back their missing electron from the microbes, thus creating a hole in the microbe wall, inhibiting microbe activity such as respiration or reproduction. Silver is commonly used in this process and other transition metals can be applied such as titanium, zinc and gold. Chemically formulated products can work on the same concept or by encapsulating the microbe.
Leaching finishes leave the textile and actively seek out microbes to destroy, making durability a challenge. The Zone of Inhibition is the area into which a substance moves to kill or inhibit a microorganism and the Zone of Adaptation is an area of sublethal dose, within which an organism can adapt accordingly to overcome the agent.
Ionised elements are generally fixed into the fibre and do not leach, therefore they do not cross the skin barrier and, for this reason, the adaptation zone is eliminated.
The introduction of nanotechnology enables these concepts to work on an even smaller scale, therefore providing a functional finish that will not affect the handle.
Toxicological and Environmental Issues
Living organisms coexist within a dependant ecosystem. As the role of antimicrobials is to inhibit or kill living things, by this definition these materials pose a threat. Chemicals that leach from textiles and are non-bioabsorbable can pose a direct threat to human health through bio disruption, adaptation of pathogens and cellular damage. The skin harbours a variety of microbes essential to its function, which serve as a natural protection from pathogens. This delicate balancing act is a challenge faced when engineering antimicrobial properties into textiles.
A further environmental factor is the activity of nanoparticles such as silver. Elements at nanoscale function differently from the bulk element, and silver nanoparticles have the ability to indiscriminately impede or kill microorganisms. There is fear that widespread use of nanoparticles such as silver will cause damage to our ecosystem.
In 1998, the European commission began obligatory publication of directive 98/8 EC, Placing Biocide products on the Market. This report was intended to replace current national laws on the 14th May 2010, following compliance of a comprehensive list of current safe-to-use products; however, this date has been extended to 14th May 2013. During this time the analysis of active substance will continue and producers and formulators are responsible for providing relevant information to support assessment and decision making.
Directive 98/8 EC Placing Biocide products on the Market
It is not a compulsory requirement to label finishes applied to apparel or Sportswear; however, many garments with microbial finishes openly advertise this, not under law but as added value.
Study on Labelling of textile products
The American Association of Textile Chemists and Colourists, the International standards organisation and the Japanese Industrial Standards, all have antimicrobial standards.
In the USA the Food and Drug Administration (FDA) regulate antimicrobial textiles intended to be used as medical devices
The United States Environmental Protection Agency (EPA) requires that treated articles intended to prevent, destroy or repel Microorganisms ?be registered under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). Under this act, no health claims can be made about the product.
The automotive industry is a market sector within which there is a growing interest in antimicrobial textile finishes and is an area that UK company BioCote have focused on when developing products for use in public transport. www.biocote.com