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The mechanisms of silver release and the sustained release of silver

Silver ions can be obtained from various donor systems such as salts, chelated structures, ion exchange systems or even metallic silver. Although they all present the same antimicrobial silver ion,Ag+, each of these donor mechanisms for silver ions have a unique activation mechanism and release profile21 . The donor system may impact the amount of silver ions released and for the rate of release, which in turn is significant for the antimicrobial effect. It is therefore important to select the right donor system and optimise the conditions for the system to obtain an optimal release profile for antimicrobial efficacy within the infected wound. An in vitro experiment has illustrated the need for a sustained silver release exposing bacteria to aconstant suppression during wear time to avoid regrowth25. A bacterial biofilm assay simulating wound bed conditions was used. A small volume of protein solution was added every day to imitate inactivation of silver by slough. Products with sustained silver release (high or low silver concentration) or no sustained release (high concentration) were compared. Products with high concentrations had the best eradication effect at day 1. However, if there was not a sustained release of silver, the bacteria re-colonised the wound bed at day 7, while products with sustained silver release (high and low) continued decreasing the bacterial load at day 7. This illustrates the need for a constant suppression of bacteria, by sustained release of silver, throughout the dressing wear time to avoid regrowth. The sustained silver release system of Biatain® Silicone Ag and Biatain Ag is based on an ion exchange system, where silver is bound to a zirconium phosphate crystal by ionic interaction with the ortho-phosphate groups in the zirconium phosphate molecule (Figure 1). The zirconium phosphate forms a sheet-like crystal with an average size of 1.3 μm wherein the silver binds in the grid structure at a loading concentration of approximately 10%.

Mechanism of silver ion release from the Biatain Silicone Ag and Biatain Ag.

Figure 1

Sustained release of silver

The release rate of silver ions varies between existing dressings on the market. Some dressings release the silver ions rapidly in either small or large amounts. Others, like Biatain® Silicone Ag and Biatain Ag, have a sustained release of silver ions over several days. In vitro release profiles from different silver dressings are shown in Figure 3. As described in the previous section, sustained release of silver ions ensures a constant, unfavourable environment for bacteria25.

The sustained silver release profile of Biatain Silicone Ag and Biatain Ag is controlled by several factors, including the volume of exudate absorbed by the dressing, the rate of cation diffusion into the zirconium crystals, the silver exchange rate and the rate of silver diffusing out into the wound bed. Biatain Silicone Ag and Biatain Ag have sustained release of silver up to 7 days (Figure 2) 26.

The release of silver from a wound dressing can be investigated in a Franz cell setup where the wound dressing is mounted in a cup exposing a specified area of the wound contact side of the dressing to a continuous flow of imitated wound fluid. The silver ions will then be released into the fluid and the release rate can be determined by measuring the silver ion concentration in the fluid by atomic absorption spectroscopy. In a study published in 201526


Biatain Silicone Ag and Biatain Agand other well-known silver dressings on the market were tested. Figure 3A shows release curves over 7 days. Biatain Silicone Ag and Biatain Ag showed a significantly greater, sustained release of silver over the 7-day period than any of the other dressings tested26.


Figure 3B illustrates how Biatain Silicone Ag and Biatain Ag with their sustained silver release profiles had the highest accumulated silver release over 7 days26.

Silver release profiles for Biatain Silicone Ag, Biatain Ag and other silver dressings.

Figure 2


The sustained release of silver by Biatain Silicone Ag and Biatain Ag is reflected in the results from a published in vitro study demonstrating antimicrobial efficacy against a wide range of pathogenic micro organisms commonly found in non-healing and infected wounds. The antimicrobial effect wascontinuous for the full 7-day test period.20

Reference list

See full list of references

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