Hacked Conductive Plastics Kill Pathogenic Bacteria

Applying a minute electrical current to an antimicrobial coating based on conjugated polymers and silver particles enhances the bactericidal effect, claims a new study.

Developed at the Karolinska Institutet (KI; Solna, Sweden), the new technology is based on antibacterial covalently coupled silver nanoparticles (AgNPs) integrated into an electrically conducting polymer layer made of a complex of poly(hydroxymethyl 3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT-MeOH:PSS) and (3-aminopropyl)triethoxysilane. The resultant composite material is thus consistently coated with covalently linked AgNPs.

The efficacy of the applied antibacterial coating--both with and without electrical charging--was tested against Staphylococcus aureus, a major colonizer of medical implants. The results showed that complete prevention of biofilm growth is obtained when the AgNP composite devices are charged with a square wave voltage input. The researchers concluded that electro-enhancement of the bactericidal effect of the coupled AgNPs offers a novel, efficient solution against biofilm colonization of medical implants. The study was published on August 14, 2017, in Advanced Healthcare Materials.

“It’s a phenomenon known as the bioelectric effect, whereby electrical fields weaken bacterial cells against external attacks,” said lead author Salvador Gomez-Carretero, MSc, a PhD student at the KI department of neuroscience. “We use electrical signals to increase the antimicrobial activity of the silver nanoparticles; this reduces the amount of silver needed, which is beneficial for both the patient and the environment.”

“By targeting the bacteria on several fronts at the same time, the effect of different small attacks becomes larger than when each factor is acting on its own,” said senior author Professor Agneta Richter-Dahlfors, phD, of the KI Medical Nanoscience Center. “It has not yet been tested in the clinic, but we believe this technology could be a good approach to limiting the spread of infectious bacteria and the incidence of hospital-acquired infections.”

The antimicrobial properties of silver are due to its ionized form (Ag+), and its ability to cause damage to cells by interacting with thiol-containing proteins and DNA. Empirically, silvers potency has been known for centuries. The Phoenicians stored water in silver coated bottles to discourage contamination; silver dollars used to be put into milk bottles to keep milk fresh, and water tanks of ships and airplanes that are "silvered" are able to render water potable for months. Out of all metals that exhibit oligodynamic antimicrobial properties, silver has the most effective antibacterial action and the least toxicity.

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