What is it about?
Textiles have the ability to retain moisture and provide a large surface area for microorganisms of all kinds to adhere to. As long as nutrients are deposited on them, bacteria and other microscopic fungi can multiply and thus damage the textile itself by deteriorating it or be a factor of contamination in sensitive environments such as health care institutions.
Antimicrobial textiles have been developed over the past 40 years: what agents are used?
Why antibacterial textiles?
In everyday life: the multiplication of micro-organisms on textiles can be responsible for various nuisances such as the formation of indelible stains by microscopic fungi on parasol cloths, for example, the modification of the mechanical properties of tent cloths or the production of bad odours by the multiplication of skin bacteria on underwear.
In healthcare settings, if the control of the spread of infections through contaminated hands, water or food is well controlled through hygiene practices, the spread of infections through textile materials can be controlled through the use of antimicrobial textiles that inhibit the growth or kill pathogens on contact before being transferred to another material or person. Indeed, it has been clearly demonstrated that textiles such as sheets, caregivers’ clothing, and even the ward manager’s tie can be responsible for the transmission of pathogens. The use of textiles with antimicrobial properties seems to be a solution to break the chain of contamination
In the year 2000, an estimated 30,000 tons of antimicrobial textiles were produced in Western Europe and 100,000 tons in the rest of the world. Socks, sportswear, shoe linings and lingerie accounted for approximately 85% of total antimicrobial textile production. In addition, a significant market for antimicrobial fibers has recently emerged in air filters, outdoor textiles, furniture fabrics and medical textiles.
The antibacterial agent must be easy to apply to textile substrates, be able to inactivate undesirable microbes while not affecting the useful flora, e.g. skin flora in the case of underwear. It must be resistant to repeated washing, dry cleaning, ironing and prolonged storage, including resistance to detergents used for textile care. It must be stable during use without degrading into dangerous by-products.
The different antimicrobials
The most commonly used antimicrobial agents for textile applications are based on metal salts (e.g., silver), quaternary ammonium compounds (QACs), halogenated phenols (e.g., triclosan), polybiguanides (e.g., PHMB), chitosan and N-halamines. Almost all commercial antimicrobial agents used in textiles (silver, polyhexamethylene biguanide (PHMB), quaternary ammonium compounds and triclosan) are biocides that kill bacteria (bactericides). They can damage the cell wall or disrupt cell membrane permeability, and inhibit enzyme activity or lipid synthesis. Others are generally bacteriostatic agents that inhibit the growth of microorganisms. Some of these products are firmly attached to the textile, others can escape, but in this case, the antimicrobial agent eventually runs out and the textile loses its effectiveness. Examples include metal salts (e.g. silver) and halogenated phenols (e.g. triclosan).
TriclosanWidely used since the 1960s for the protection of hygiene products, it is one of the most controversial products because, when destroyed by heat, it releases dioxin and, when present in small quantities, it acquires antibiotic properties, whose action presents cross-reactions with certain anti-tuberculosis drugs: it is banned in many countries.
QAC Quaternary ammonium
QACs are active against a wide range of microorganisms such as fungi, Gram-positive and Gram-negative bacteria, and some viruses.
The cationic ammonium group and the negatively charged bacterial membrane are attracted to each other. As a result, the interactions lead to the formation of a surfactant-microbe complex that interrupts all normal membrane functions. QACs also affect bacterial DNA, resulting in the loss of the ability to multiply. In addition, penetration of the hydrophobic group into the microorganism, can also occur allowing the alkylammonium group to physically interrupt all key functions of the cell. Quaternary ammonium compounds are therefore membrane active agents, their target site being the cytoplasmic membrane in bacteria or the plasma membrane in yeast. One of the proposed mechanisms involves the adsorption and penetration of CAQs into the cell wall of the microorganism and then the reaction with the lipid or protein cytoplasmic membrane, which, by disorganizing, allows the escape of low molecular weight intracellular material. Nucleic acids and proteins are degraded. The wall is lysed by autolytic enzymes.
At the toxicity level, CAQ are known to be allergens (asthma, contact dermatitis) when they are in powder form or in solution, which is not the case when they are attached to textiles.
Polyhexamethylene biguanide (PHMB)
PHMB is a heterodisperse mixture of polyhexamethylene biguanide. Already used as a disinfectant for swimming pools, mouthwashes, dressings and in the food industry. PHMB disrupts the integrity of cell membranes.
N-halamines and regenerable peroxyacids
N-halamines are heterocyclic compounds containing one or two covalent bonds formed between the nitrogen and a halogen. The halogen, which is usually chloride, is replaced by hydrogen in the presence of water and acts as a biocide.
N-Cl is converted to N-H, which can be recharged to chlorine for example during bleaching, using bleach. N-H is then converted to N-Cl. Two mechanisms can be used to explain the antibacterial activity of N-chloramine. The first mechanism is that the chlorine is released into the water and forms HClO or ClO-. The other is that chlorine binds directly to the acceptor regions of bacteria and significantly influences enzymatic and metabolic processes.
However, N-halamine materials decompose when exposed to ultraviolet light, as is the case in direct sunlight. The main problem with N-halamines is that they produce a significant amount of absorbed chlorine (or perhaps other halogens), which can remain on the surface of the fabric, causing an unpleasant odor and discoloration of the fabric. The use of bleach and the presence of strong oxidants degrade the dye in the textile, resulting in discoloration.
Another antibacterial agent are peroxyacids (such as peroxyacetic acid, which is widely used in hospitals). Peroxyacids must convert to a carboxylic acid in order to inactivate bacteria, but can be regenerated by reacting with an oxidant (such as hydrogen peroxide). Despite the stability of peroxyacids on the fabric for extended periods of time, antibacterial activity largely decreases after a number of wash and recharge cycles
Chitosan and its derivativesChitosan is derived by deacetylation of chitin, the main component of shrimp, crab and lobster shells. The most common antibacterial activity of chitosan is to bind to the negatively charged bacterial cell wall, which changes the permeability of the membrane, and then binds to DNA, inhibiting its replication before causing cell death.
Since chitosan does not dissolve in aqueous media at neutral and alkaline pH, nor is its antimicrobial activity particularly good in neutral or alkaline solutions, there are many reasons to chemically modify chitosan. These modifications are made in order to provide more soluble and textile-friendly chitosan derivatives. Chitosan can be modified to include quaternary ammonium groups, alkyl and aromatic groups, substituents with free amino or hydroxyl groups, carboxyalkyl groups and amino acids and peptides. Examples of chitosan derivatives include carboxymethyl chitosan, N,N,N,-trimethyl chitosan (TMC) and Chitosan nanoparticles (CSNP).
To determine the antibacterial activity of a textile, standardized methods are used. They are numerous and are divided into qualitative and quantitative tests.
For qualitative tests, a piece of textile is placed on a bacterial culture in the manner of an antibiogram (NF EN ISO 20645). After incubation, the formation of a halo without bacterial culture around the sample indicates that there is an antibacterial action by diffusion of the agent which is not always desirable because of a possible migration of the product in the body and because this product is necessarily exhausted in the course of time (see top image).
For quantitative methods, in France the reference method is NF EN ISO 20743 Textiles – Determination of the antibacterial activity of antibacterial finished products. This method consists in measuring the quantity of bacteria in 24 hours in a standardized culture medium in the presence of the active textile and to compare it to that obtained in the presence of a control textile without antibacterial agent.
In addition to antibacterial textiles, antiviral and antifungal textiles have been developed. Active agents can also be integrated into solid surfaces to provide additional hygiene, for example on restaurant tables, kitchen surfaces, floor coverings, or even banknotes, which are also major sources of cross-contamination.
Antibacterial textiles are still relevant today and this very complete article allows us to take stock of those that have resisted over time among all those that have been tested. The bibliography is very complete.
This article can be found online here.