Enhanced copper surface kills bacteria in minutes

Researchers from RMIT University and CSIRO have developed a new copper product that kills bacteria more than 100 times faster and more effectively than standard copper, and could therefore help combat the growing threat of antibiotic-resistant superbugs. Their findings have been published in the journal Biomaterials.

As explained by CSIRO’s Dr Daniel Liang, researchers across the world are looking to develop new medical materials and devices that can help reduce the rise of antibiotic-resistant superbugs by reducing the need for antibiotics.

“Drug-resistant infections are on the rise and, with limited new antibiotics coming onto the market, the development of materials resistant to bacteria will likely play an important role in helping address the problem,” Dr Liang said.

An example of a potent microbial is nanosilver, which is currently used in medical devices such as internal catheters and wound dressings to fight or prevent infections, and has also been incorporated into consumer products from soap and toothpaste to washing machines and fridges. Unfortunately, researchers at the University of Technology Sydney’s (UTS) ithree institute recently discovered that pathogens that form biofilms can evolve to survive nanosilver treatment. Following prolonged treatment, nanosilver killed 99.99% of the bacterium Pseudomonas aeruginosa with 0.01% of cells surviving for longer — and this minute fraction of ‘persisters’ resumed normal growth upon discontinuation of the treatment.

Copper is another material that has long been used to fight different strains of bacteria, including the commonly found golden staph, because the ions released from the metal’s surface are toxic to bacterial cells. But this process is slow when standard copper is used, said RMIT Distinguished Professor Ma Qian, and significant efforts are underway to speed it up.

“A standard copper surface will kill about 97% of golden staph within four hours,” Prof Qian said.

“Incredibly, when we placed golden staph bacteria on our specially designed copper surface, it destroyed more than 99.99% of the cells in just two minutes.

“So not only is it more effective, it’s 120 times faster.”

Images magnified 120,000 times under a scanning electron microscope show golden staph bacteria cells after two minutes on a) polished stainless steel, b) polished copper, and in c) and d), the team’s micro-nano copper surface.

Importantly, these results were achieved without the assistance of any drug — rather, it is the copper’s unique porous structure that is key to its effectiveness as a rapid bacteria killer.

A special copper mould casting process was used to make the alloy, arranging copper and manganese atoms into specific formations. The manganese atoms were then removed from the alloy using a cheap and scalable chemical process called ‘de-alloying’, leaving pure copper full of tiny microscale and nanoscale cavities in its surface.

“Our copper is composed of comb-like microscale cavities and within each tooth of that comb structure are much smaller nanoscale cavities; it has a massive active surface area,” said former CSIRO researcher Dr Jackson Leigh Smith, lead author on the new study.

The copper magnified 2000 times under a scanning electron microscope shows its unique micro-comb structure.

The copper magnified 500,000 times under a scanning electron microscope shows the tiny nanoscale pores in the structure.

“The pattern also makes the surface super hydrophilic, or water-loving, so that water lies on it as a flat film rather than as droplets.

“The hydrophilic effect means bacterial cells struggle to hold their form as they are stretched by the surface nanostructure, while the porous pattern allows copper ions to release faster.

“These combined effects not only cause structural degradation of bacterial cells, making them more vulnerable to the poisonous copper ions, but also facilitates uptake of copper ions into the bacterial cells.

“It’s that combination of effects that results in greatly accelerated elimination of bacteria.”

The team believes there could be a huge range of applications for the new material once further developed, including antimicrobial doorhandles and other touch surfaces in schools, hospitals, homes and public transport, as well as filters in antimicrobial respirators or air ventilation systems, and in face masks.

With patents currently pending in the US, China and Australia, the team is now looking to investigate their enhanced copper’s effectiveness against SARS-CoV-2, including assessing 3D-printed samples. Other studies have suggested that copper may be highly effective against the virus, leading the US Environmental Protection Agency to officially approve copper surfaces for antiviral uses earlier this year.

“This new copper product offers a promising and affordable option to fighting superbugs, and is just one example of CSIRO’s work in helping to address the growing risk of antibiotic resistance,” Dr Liang concluded.

Top image credit: ©stock.adobe.com/au/Rawpixel.com

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