A self-disinfecting plastics film coated with silver and calcium phosphate has been developed by a research group led by Wendelin Stark, Assistant Professor at the Institute for Chemical and Bioengineering of ETH Zurich. This innovative product that is lethal to bacteria has been developed with a special feature-namely that the bacteria themselves invoke and dispense this disinfectant effect. As an example, the combination of the two substances has an effect on the bacterium Escherichia coli that is up to 1000 times more lethal than conventional silicon-based silver preparations.
The calcium phosphate particles, 20-50 nanometers in size, are absorbed by the micro-organisms as food and are thereby disintegrated. This releases thousands of tiny silver particles measuring 1-2 nanometers which the researchers had coated onto the calcium nutrient.
Silver nanoparticles have multiple effects on bacteria: they suppress the cell's nutrient transport, attack the cell membrane and interfere with cell division and thus with the reproduction of the germs. Experiments with the carrier substances calcium phosphate and silicon dioxide, each coated with silver, showed different effects on various bacterial strains in the test. The calcium phosphate substrate had an efficiency factor of upto 1000 times stronger than silicon dioxide. Within 24 hours, less than one bacterium out of 100,000-1,000,000 bacteria survived.
However, according to the researchers, since the consumption of the organic calcium phosphate also nourishes the bacteria - without the effect of the silver, they would multiply thousand-fold in 24 hours - the silver must fight not only the bacteria that already exist but also those that would newly form.
The new product has enabled the group to successfully develop a preparation that is effective against a series of pathogenic bacteria and which becomes active in a targeted manner and in the correct dose only if a bacterium is present. The silver adhering to the calcium phosphate is only released in a quantity corresponding to the amount of calcium phosphate consumed by the bacterium. This saves costs, is efficient and is less stressful for the human body. The product is already being manufactured by the Perlen Converting AG Co., which was involved in the development.
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