Antimicrobial surfaces

Systemic antibiotic treatment is a very common medical procedure all over the world. Nevertheless, it presents certain limitations and drawbacks, such as systemic toxicity, poor penetration in certain tissues, and poor control of local drug levels. Additionally, in the case of implantable medical devices, if bacteria (typically 5. aureus, S. epider-midis. Pseudomonas aeruginosa, E. colt, etc. ) adhere and proliferate, colonizing the implant surface and forming a biofilm, the patient may develop an infection despite systemic antibiotic treatment, which may lead to the rejection or removal of the implant (Fig. 10). Actually, an implant represents a challenge to the immune system. 

Current solutions and developments in the field of antimicrobial surfaces include, among others, silver (or other antibacterial element) containing coatings and surfaces, photocatalytic TiOi surfaces, bacterial adhesion inhibiting surfaces, and antibiotic loaded coatings.  

The possibility of photocatalytic disinfection in Ti02 under UV light irradiation has also been extensively studied, e.g. magnetron sputtered or plasma ion implanted 

Ti02 thin film, or Fe plasma ion implanted Ti02 irradiated with visible light have shown antimicrobial activity.  

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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. 

Abstract In this review, the general principles of antimicrobial surfaces will be discussed in detail. Because many common products that keep microbes off surfaces have been banned in the past decade, the search for alternatives is in full run. In recent research, numerous new ways to produce so-called self-sterilizing surfaces have been introduced. These technologies are discussed with respect to their mechanism, particularly focusing on the distinction between biocide-releasing and non-releasing contact-active systems. New developments in the catalytic formation of biocides and their advantages and limitations are also covered. The combination of several mechanisms in one surface modification has considerable benefits, and will be discussed. 

This chapter is dedicated to discussion of the state of the art of antimicrobial surfaces, particularly with respect to their mechanism of action. 

Many microbial infections and toxins are spread by biofilms. Biofilm formation occurs on virtually every surface, starting with the adhesion of planctonic cells or small dispersed biofilm fragments. Proliferation of the cells is accompanied by the expression of an extracellular polysaccharide-based matrix [6], The cells embedded in this matrix are well protected and up to 1000 times less susceptible to antibiotics [7], Once a biofilm is formed, it is extremely difficult to remove this contamination. Thus, all antimicrobial surfaces should prevent the primary attack [8], One class of antimicrobial surfaces prevents the primary attack by creating surfaces that are not sticky to microbial cells, i.e., they do not allow adhesion of these cells. The other major class of antimicrobial surfaces is based on the killing of approaching microbes (see Fig. 2). Interestingly, both approaches can be achieved either by permanent surface modifications or by releasing bioactive compounds. 

Another kind of contact-active antimicrobial surface was achieved by tethering antimicrobial peptides to surfaces [62], If such peptides were exclusively membrane-active they could not work like in solution but would be immobilized via a polymeric spacer that could potentially cross the cell wall. The latter was demonstrated by the group of Dathe, who immobilized cationic antimicrobial peptides on PentaGels [63], Also, the well-known antimicrobial peptide magainin I... 

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 use of electric current as hydrogen-peroxide-releasing antimicrobial surface has been discussed in Sect. 4 [84],... 

A novel approach is the development of multifunctional antimicrobial surfaces that work synergistically and are therefore very promising for the future. 

Antimicrobial surfaces are still in the focus of academic and industrial research. One important issue for new developments is to find the true mechanism of existing and new antimicrobial surfaces, because only that knowledge allows useful predictions for their optimization in terms of reactivity and long-term activity. 

Gettings RL, White WC (1987) Formation of polymeric antimicrobial surfaces from organofunctional silanes. Polym Mater Sci Eng 57 181-185... 

Kurt P, Wood L, Ohman DE et al. (2007) Highly effective contact antimicrobial surfaces via polymer surface modifiers. Langmuir 23 4719-4723... 

Madkour AE, Dabkowski JM, Nusslein K et al. (2009) Fast disinfecting antimicrobial surfaces. Langmuir 25 1060-1067... 

Page K, Wilson M, Parkin IP (2009) Antimicrobial surfaces and their potential in reducing the role of the inanimate environment in the incidence of hospital-acquired infections. J Mater Chem 19 3819-3831... 

Antimicrobials. Surface-bonded organosilicon quaternary ammonium chlorides have enhanced antimicrobial and algicidal activity (33). Thus, the hydroysis product of dimethyloctadecyl-3-trimethoxysilylpropylammonium chloride [27668-52-6] exhibits antimicrobial activity against a broad range of microorganisms while chemically bonded to a variety of surfaces. The chemical is not removed from surfaces by repeated washing with water, and its antimicrobial activity is not attributed to a slow release of the chemical but rather to the surface-bonded chemical. 

These products permit a slow rate of release of silver ions and therefore minimise the discoloration associated with silver chemicals. It is claimed that moisture in the air causes low-level release that effectively maintains an antimicrobial surface. As humidity increases and the environment becomes ideal for bacterial growth, more silver is released to a maximum level. Silver ions are said to be effective by interacting with multiple binding sites on the surface of the bacterial cell wall. 

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