domingo, 27 de agosto de 2006

Silver Bromide Shines In Bacteria-Fighting Coating

Polymer-nanoparticle composite could ward off infections associated with implanted biomedical devices
Bethany Halford
A new type of antimicrobial coating could make it easier and cheaper to endow biomedical implants with the bacteria-fighting power of silver. The material, a cationic polymer embedded with AgBr nanoparticles, is relatively simple to synthesize and overcomes solubility problems associated with other types of silver-based antimicrobial coatings, according to the Pennsylvania State University chemists who invented it (J. Am. Chem. Soc. 2006, 128, 9712).
Ayusman Sen, Varun Sambhy, Megan M. MacBride, and Blake R. Peterson prepare the composite coating by adding a silver salt to the cationic copolymer poly(4-vinylpyridine)-co-poly(4-vinyl-N-hexylpyridinium bromide). This leads to the precipitation of AgBr nanoparticles, which are stabilized by the capping and steric effect of the polymer.
"To the best of our knowledge, this is the first example of use of an on-site precipitation technique to directly synthesize polymer-nanoparticle composites in a single step," Sen says.
Most silver-based antibacterial coatings use elemental silver or complex silver compounds to generate the biocidal Ag+ ion. Using AgBr, the authors say, makes the Ag+ ions more readily available than elemental silver, and because AgBr is sparingly soluble, there's no uncontrolled dissolution of silver as is common with other silver compounds.
The coatings can kill gram-positive and gram-negative bacteria on surfaces and in solution. They therefore could be used to ward off infection from biomedical devices, such as catheters, prosthetics, and implants. Sen tells C&EN that the coating's ability to fight methicillin-resistant Staphylococcus aureus, a common source of deadly infections in hospitals, is particularly promising. "The effectiveness of our composites against this bacterial line suggests their use as persistent antiseptic coatings for hospital surfaces and other surfaces that come into frequent human contact," he says.
The research "looks like an exciting new technology that could solve a lot of the infection problems associated with nosocomial infections and biofilm formation," says Daniel M. Storey, chief technical officer at Nexxion, a Longmont, Colo.-based company that manufactures silver-based antimicrobial coatings. "Silver is more and more becoming recognized as a highly effective antimicrobial due to bacteria's inability to adapt to the damage caused by silver ions," Storey adds.
Chemical & Engineering News
ISSN 0009-2347
Copyright © 2006 American Chemical Society

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