Sustained Silver Release
The topical antimicrobial agent silver has been used for hundreds of years in wound care. For example, silver has been used to prevent or manage infection in its solid elemental form (eg silver wire placed in wounds), as solutions of silver salts used to cleanse wounds (eg silver nitrate solution), and more recently as creams or ointments containing a silver–antibiotic compound (silver sulfadiazine (SSD) cream). 1
Silver nitrate solution is less widely used nowadays, but SSD cream has been an important part of burns management for many years. SSD cream, however, is relatively short-acting, requires reapplication at least daily, and is time-consuming and messy to apply and remove.
In recent years, a wide range of wound dressings that contain elemental silver or a silver-releasing compound have been developed. These dressings have overcome some of the problems associated with the first silver preparations. They are easier to apply, may provide sustained availability of silver, may need less frequent dressing changes, and may provide additional benefits such as management of excessive exudate, maintenance of a moist wound environment, or facilitation of autolytic debridement.
The History of Silver
FORYOU MEDICAL have dedicated years’ of hard work and have successfully developed and launched a Slow Silver Releasing Antibacterial Technology with independent intellectual property rights. Currently, our antibacterial dressing product series, including LUOFUCON® Silver Alginate Dressing, Silver Foam Dressing and Silicone Ag Foam Dressing, have become our competitive edge in the global wound care market.
Research suggests that only a small proportion of silver presented to a wound site in a dressing is involved in antimicrobial action. Most of the rest remains within the dressing or binds to proteins in the wound or wound debris. Very little is systemically absorbed.Even if absorbed systemically, silver is excreted mainly via the biliary route in faeces. Some is also excreted in urine. Silver is not absorbed into the central or peripheral nervous systems.
In metallic (elemental) form, silver is unreactive and cannot kill bacteria. To become bactericidal, silver atoms (denoted as Ag or Ag0) must lose an electron and become positively charged silver ions (Ag+). Elemental silver ionises in air, but ionises more readily when exposed to an aqueous environment such as wound exudate. In contrast, silver compounds contain positive silver ions bound to negatively charged ions or molecules. When exposed to aqueous environments, some of the silver ions become detached from the compound.
Silver ions are highly reactive and affect multiple sites within bacterial cells, ultimately causing bacterial cell death. They bind to bacterial cell membranes, causing disruption of the bacterial cell wall and cell leakage. Silver ions transported into the cell disrupt cell function by binding to proteins and interfering with energy production, enzyme function and cell replication. Silver ions are active against a broad range of bacteria, fungi and viruses, including many antibiotic-resistant bacteria, such as meticillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococci (VRE).
Antibacterial Mechanism of Silver
Some laboratory studies have suggested that silver may have beneficial effects on wound healing other than the control of bioburden alone. For example, silver nitrate, nanocrystalline silver, and some silver-containing dressings have been found to have anti-inflammatory effects and to encourage blood vessel formation (neovascularisation). The clinical relevance of these findings is not yet known.
The use of silver dressings can effectively alleviate the dependence of clinical nursing on antibiotics and make more choices in the treatment of wound infection. FORYOU MEDICAL will continue to study silver antimicrobial dressings and other antibacterial products in order to contribute to the fight against bacterial resistance.
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Anti-Biofilm Activity -- Challenge The Biggest Problem of Repeated Infection
Biofilms are complex microbial communities, containing bacteria and sometimes also fungi, which are embedded in a protective polysaccharide matrix. The matrix attaches the biofilm to a surface, such as a wound bed, and protects the microorganisms from the host's immune system and from antimicrobial agents such as antiseptics and antibiotics. Biofilms are commonly present in chronic wounds, and are thought to contribute to, and perpetuate, a chronic inflammatory state that prevents healing. 2
Currently, the management of biofilms involves:
· Reduction of biofilm burden through debridement and/or vigorous cleansing to remove the biofilm and the dormant (persister) bacteria.
· Prevention of biofilm reformation through the use of topical antimicrobials to kill planktonic (free-floating) bacteria.
Studies of the effects of silver dressings on experimental models of biofilms have suggested that silver may reduce bacterial adhesion and destabilise the biofilm matrix, as well as kill bacteria within the matrix and increase susceptibility of bacteria to antibiotics. Many studies have confirmed this point, but further research is needed for a clearer mechanism.
Other Effects of Silver
1. International consensus. Appropriate use of silver dressings in wounds. An expert working group consensus. London: Wounds International, 2012 Available to download from: www.woundsinternational.com
2. Phillips PL, Wolcott RD, Fletcher J, Schultz GS. Biofilms Made Easy. Wounds International 2010; 1(3): Available from http://www.woundsinternational.com
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