Silver-containing wound dressings

Silver has broad-spectrum antimicrobial properties and a low level of toxicity to the human body. In recent years, as bacterial resistance to antibiotics became common and more and more attention was paid to cross-infection in hospital wards, wound dressings with antimicrobial properties became increasingly popular. Silver is gaining in importance as an effective antimicrobial component in advanced wound dressings. 

The antimicrobial action of silver products has been directly related to the amount and rate of silver released and its ability to inactivate target bacterial and fungal cells. In varions laboratory and clinical studies it has been found that metallic silver does not possess significant antimiCTobial potency, while silver ions are highly antimicrobial. The oligodynamic microbicidal action of silver compounds at low concentrations probably does not reflect any remarkable effect of a comparatively small number of ions on the cell, but rather the ability of bacteria, trypanosomes, and yeasts to take up and concentrate silver from very dilute solutions. Therefore bacteria killed by silver may contain 10 -10 Ag+ per cell, the same order of magnitude as the estimated number of enzyme-protein molecules per ceU. 

Chemically, metallic silver is relatively inert, but its interaction with moisture on the skin surface and with wound fluids leads to the release of silver ions and their biocidal properties. Silver ions are highly reactive moieties and avidly bind to tissue proteins, causing structural changes in bacterial cell walls and intracellular membranes, which lead to cellular distortion and loss of viability. Silver ions bind to and denature bacterial DNA and RNA, thereby inhibiting replication. 

A recent study demonstrated the inhibitory action of silver on two strains of gram-negative Escherichia coli and gram-positive S. aureus. It was found that exposure to silver nitrate led to the formation of electron-light regions in their cytoplasm and 

The action of silver ions on cell walls is iUuslrated by reference to the yeast Candida albicans. Silver has been shovm to inhibit the enzyme phosphomannose isomerase by binding cysteine residues. This enzyme plays an essential role in the synthesis of the yeast cell wall, and its defects lead to the release of phosphate, glutamine, and other vital nutrients. 

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Table 11.1 Silver compounds used in silver-containing wound dressings...

Table 11.1 summarizes the various silver compounds used in some of the many silver-containing wound dressings. 

The silver-containing wound dressings currently available have considerable differences in their overall structures, the concentration and formulation of the silver compounds, and the base materials used to carry the silver compounds. Many methods have been developed to incorporate silver into wound dressings. In general, these methods can be classified into the following four types. 

In a detailed study on the performance of various silver-containing wound dressings, Thomas found that when testing against S. aureus ... 

Cost effectiveness is a practical issue with silver-containing wound dressings, since they are generally more expensive than conventional ones. However, a thorough assessment of the cost effectiveness of a healthcare intervention is complicated and involves many factors, including resource use, quality-of-life issues, and economic parameters such as the ability to work. Silver-containing wound dressings have been found to be cost effective for a number of reasons, such as ... 

As more and more silver-containing wound dressings are used, concerns have been raised that silver released into the environment may be harmful. In this respect, silver is used worldwide in a wide range of technologies and the environmental impact of silver is not clear. However, compared to silver released from other sources, wound dressings represent only a very small proportion of global annual silver consumption, accounting for about 0.0008%. 

Castellano, J. J., S. M. Shafii, et al. (2007). Comparative evaluation of silver-containing antimicrobial dressings and drugs. International Wound Journal 4(2) 114-122. 

Table 4 A 30 minute bactericidal (log reduction) assay comparison of a poly-nanocrystalline silver dressing (Acticoat ), against 7 other silver containing wound treatments. Silver nitrate and silver sulfadiazine (SSD) are a 0.5% solution and a 1% cream, respectively...

Thomas, S., McCubbin, P., 2003. An in vitro analysis of the antimicrobial properties of 10 silver-containing dressings. Journal of Wound Care 12, 420. 

Rujitanaroj, P.O. Pimpha, N. SupaphoL P. Wound-dressing materials with antibacterial activity from electrospun gelatin fiber mats containing silver nanoparticles. Polymer 2008, 49 (21), 4723-4732. 

Chen J-P, Chiang Y. Bioactive electrospun silver nanoparticles-containing polyurethane nanofibers as wound dressings. 7 Aanoici Nanotechnol 2010 10(11) 7560—4. 

Percival, S.L., Bowler, P.G.,and Dolman, J. Antimicrobial activity of silver-containing dressings on wound microorganisms using an in vitro biofilm model. Int Wound J., 4, 186-191 (2007). 

Chemical treatment of the base material In this method, the fiber or fabric can be treated with silver-containing solutions, whereby silver ions can be attached to the wound dressing through ion exchange. 

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