Antimicrobial surfaces/materials

There are many applications in the medical and food sanitization fields for which antimicrobial surface coatings are needed. There are commercially available products making antibacterial claims, but they are limited in their applications by such factors as a poor spectra of activity, high cost, and toxicity. Work in the laboratories at Auburn Uifiversity over the past two decades has established a novel class of heterocyclic orgaific compounds termed A-halamines that have been demonstrated to be excellent antimicrobial materials for a broad variety of applications. 

Repelling microbes or killing them on contact are obviously the optimal ways for an antimicrobial surface to function. However, most moist and biologically contaminated areas contain large amounts of material that nonspeciflcally attach to a surface and deactivate it fully. Furthermore, high concentrations of microbes will eventually cover any surface with dead cells, which also deactivate the surface. In the latter case, only surfaces that release biocides will retain their activity. 

The increasing occurrence of microbial and nosocomial infection has stimulated research activities into antimicrobial polymers and textiles [19, 25, 34]. Most medical textiles and polymeric materials used in hospitals are conductive to crosstransmission of diseases, as most microorganisms can survive on these materials for hours to several months [17, 26]. Thus, it would be advantageous for polymeric surfaces and textile materials to exhibit antibacterial properties so as to reduce and prevent disease transmission and cross-contamination within and from hospitals. N-halamines exhibit a similar antimicrobial potency to chlorine bleach, one of the most widely used disinfectants, but they are much more stable, less corrosive and have a considerably reduced tendency to generate halogenated hydrocarbons, making them attractive candidates for the production of antimicrobial polymeric materials. N-halamine compounds are currently used as antimicrobial additives to produce polymers with antimicrobial and biofilm-limiting activities. 

As previously indicated, many microorganisms produce EPS or slime, and several researchers have investigated the role of EPS in corrosion [86-88]. EPS consist of polysaccharides and proteins, plus significant amounts of nucleic acids, (phospho) lipids and humic substances [89-91]. The final composition of the EPS matrix results from a combination of the following active secretion, shedding of cell surface material, cell lysis, and/or adsorption of substances from the environment. EPS are usually acidic and contain functional groups, such as carboxylic and amino acids that, as mentioned earlier, readily bind metal ions. EPS can bind metal ions from the substratum or from a liquid medium and control interfacial chemistry at a metal/biofilm interface. EPS are also implicated in increased resistance of biofilm cells to biocides and other antimicrobial compounds [9]. 

U. Konwar, N. Karak and M. Mandal, Vegetable oil based highly branched polyester/clay silver nanocomposites as antimicrobial surface coating materials , Prog Org Coat, 2010, 68, 265-73. 

Developments in nanotechnology to provide antimicrobial surfaces and materials... 

It is important to note that antimicrobial and biofilm resistance are two different characteristics though some materials show both properties at the same time. Antimicrobial materials do not automatically prevent biofilm formation and vice versa. Antimicrobial surfaces could kill bacteria on contact but if dead bacteria cell debris blocks the active biocidal surface, biofilm formation could eventually occur. For example, quaternary anunonium polymers can effectively kill bacteria but when the surface is fouled with dead bacteria debris, biofilm formation is inevitable [188]. Materials with antibiofilm properties will repel the bacterial adhesion very effectively but may not kill the bacteria when they do colonize the surface. PEG surfaces are well known to repel bacteria adhesion. However, PEG surfaces show little antimicrobial activity. Quantitative antibiofilm efficacy tests can be divided into two categories static (minimum biofilm eradication concentration assay, MBEC) and dynamic (flow cell assay). In addition, SEM is a semiquantitative assay, which is discussed in Section 2.5. 

In general, antimicrobial packaging materials must be in contact with the food if they are nonvolatile. The antimicrobial agents can diffuse to the surface during service. For this reason, the surface characteristics and the diffusion kinetics are important issues. 

Page, K., M. Wilson, et al. (2009). Antimicrobial surfaces and then-potential in reducing the role of the inanimate environment in the incidence of hospital-acquired infections. Journal of Materials Chemistry 19(23) 3819-3831.. 

The threat of accidental misuse of quaternary ammonium compounds coupled with potential harmful effects to sensitive species of fish and invertebrates has prompted some concern. Industry has responded with an effort to replace the questionable compounds with those of a more environmentally friendly nature. Newer classes of quaternaries, eg, esters (206) and betaine esters (207), have been developed. These materials are more readily biodegraded. The mechanisms of antimicrobial activity and hydrolysis of these compounds have been studied (207). AppHcations as surface disinfectants, antimicrobials, and in vitro microbiocidals have also been reported. Examples of ester-type quaternaries are shown in Figure 1. 

An alternative packaging is the combination of food-packaging materials with antimicrobial substances to control microbial surface contamination of foods. For both migrating and nonmigrating antimicrobial materials, intensive contact between the food product and packaging material is required and therefore potential food applications include especially vacuum or skin-packaged products (Vermeiren and others 2002). 

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