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Posted: Sep 24, 2012

The overrated precious metal - Silver is not an innocuous germicide after all

(Nanowerk News) Silver, an element long favored by medicine for its antiseptic properties, turns out to be damaging to human fibroblasts when used in the dosages required to be effective. Furthermore, the presence of albumin weakens silver’s ability to fight bacteria. These findings were recently made by a team of researchers working under the direction of Dr. Stephan Barcikowski, a professor with the Center for Nanointegration (CENIDE) at University of Duisburg-Essen (UDE). The findings have been published in three consecutive papers.
The team conducted a series of tests examining the antibacterial activities of silver nanoparticles that the researchers produced themselves using laser technology ("Synthesis of hybrid microgels by coupling of laser ablation and polymerization in aqueous medium"). The scientists bound the nanoparticles to various synthetic materials so that they would not be absorbed by the body but would remain effective, because their large surfaces emit enough silver ions. It is these ions that are, in fact, the active substances that, for example, kill bacteria at a wound, reducing the risk for infection. Silver is therefore a substance well-suited for preserving medical products or for covering burn wounds.
Experiments using various bacteria conducted in collaboration with the clinic at the Hannover Medical School under the direction of Dr. Meike Stiesch confirmed silver’s germicidal properties. Subsequent studies, however, demonstrated that at the concentrations required for killing bacteria, the silver ions also damaged fibroblasts to a significant degree. “We hadn’t expected this to be the case, of course, given that silver is already widely used throughout medicine,” said Barcikowski, Chair of Technical Chemistry I at the UDE and editor-in-chief of the journal BioNanoMaterials. “But further testing proved that it was the ions themselves that were damaging the cells and not, as we had at first suspected, the synthetic materials.” When the scientists then mixed the samples with albumin, silver’s antibacterial effectiveness dropped, but the damaging effect on the cells remained the same. The therapeutic margin is therefore extremely narrow in this case, making med ical applications risky ("Therapeutic Window of Ligand-Free Silver Nanoparticles in Agar-Embedded and Colloidal State: In Vitro Bactericidal Effects and Cytotoxicity").
Further studies are currently investigating whether it is possible to use the wound-healing properties of nanomaterials in a targeted manner. The study, “In-situ conjugation of nanoparticles using ultra-short pulsed laser ablation in monomer solution for electrospinning at burn wound sites,” which is part of the DFG Priority Program 1327 “Sub-100 nm Structures,” is currently looking into this. In collaboration with RWTH Aachen University and the Hannover Medical School, a team, also under the direction of Barcikowski, is researching whether nanoparticles composed of milder substances, such as zinc, iron, and magnesium, can be used to heal burn wounds. The researchers would like to test less harmful nanomaterials and then make them usable for therapeutic purposes ("Serum albumin reduces the antibacterial and cytotoxic effects of hydrogel-embedded colloidal silver nanoparticles").
Source: CENIDE
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