A team led by Wendelin Stark, assistant professor at the Institute for Chemical and Bioengineering of ETH Zurich, said that it has developed a self-disinfecting polymer that is effective against pathogenic bacteria and only becomes active in a targeted manner if bacteria are growing in the vicinity, making it cost effective.

The research group’s findings, published in the science journal, Small, ​demonstrate that the film is significantly more lethal against the bacterium E coli​ than conventional silicon-based silver preparations. “Within 24 hours of the plastic film being applied to a surface, less than one bacterium out of one million bacteria will survive,”​ claims Stark.

Wide applications​

The film will be of interest to food manufacturers as microbial growth can affect food quality and safety and can damage a firms reputation and profits following costly recalls.

Stark told FoodProductionDaily.com that both the food handling and processing industries could benefit from self-sterilizing surfaces. He said that areas like walls, machine covers and conveyor belts could be covered with the film to inhibit recontamination from product-touching surfaces.

“We also see particularly interesting applications in terms of the packaging of perishables like meat, fish, pastry and convenience food,”​ added Stark.

Stark said that the patent protected active ingredient, which renders surfaces self-sterilizing, can already be obtained through a spin-off company of ETH Zurich called Nanograde GmbH.

He added that the inventors are interested in giving out specific licenses in terms of large-scale applications.

Germ-fighting properties ​

Current methods for rendering surfaces antibacterial are the use of synthetic peptides, the design of surfaces to hinder bacterial adhesion and materials that release antimicrobial agents, such as antibiotics, according to the study.

The researchers said their project was motivated by concerns over increasing antibiotic resistance in humans and the growing demand for alternatives to antibiotic releasing antimicrobial agents.

According to the chemical engineers, silver has traditionally been used as an antiseptic and disinfectant and recent studies have found that impregnating other materials with silver nanoparticles is a practical way to exploit its germ-fighting properties, in particular because of its low toxicity to humans.

Major consumer goods manufacturers already produce goods that utilise the antibacterial properties of silver nanoparticles. Current applications for silver nanoparticle-impregnated materials include household items, clothing (for example, socks to prevent foot infections for soldiers deployed in jungles), and laundry detergents.

Technology​

Polymer surfaces containing silver on calcium phosphate nanoparticles were tested on a series of bacteria including A. ​niger​, S. aureus, P. aeruginosa ​and E. coli.​

Stark explained that the project is informed by the fact that bacteria rely on calcium for their metabolism and as such the calcium phosphate particles are used by the micro-organisms as nutrition.

“When the bacteria consume the calcium phosphate, thousands of small silver nanometre particles are released. It is these tiny silver particles that kill the bacteria and prevent germs from growing and spreading,”​ said Stark.

The researchers claim that this is the first time that silver has been applied in this targeted and measured way.

Results​

The team said they conducted experiments with carrier substances calcium phosphate and silicon dioxide, each coated with the silver nanoparticles, and each showed different effects on various bacterial strains in the test.

The calcium phosphate substrate had an efficiency factor of up to 1,000 times stronger than silicon dioxide on E. coli, claims the study, with a five to six log reduction after 24 hours.

Source: Small ​2008, 4 (6)​, 824-832Published online ahead of print: doi:10.1002/smll.200800047“Micro-organism-triggered release of silver nanoparticles from biodegradable oxide carriers allows preparation of self-sterilizing polymer surfaces.”​Authors: Loher, S. et al.