A team of materials scientists from RMIT University and CSIRO has designed and fabricated a micro-nano copper structure and demonstrated its exceptional bactericidal efficacy against the common and deadly Staphylococcus aureus bacteria. The researchers believe 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.
The copper magnified 500,000 times under a scanning electron microscope shows its tiny nano-scale pores. Image credit: RMIT University.
Conventional copper has long been used to fight different strains of bacteria, including the commonly found Staphylococcus aureus, because the ions released from the metal’s surface are toxic to bacterial cells.
But this process is slow when standard copper is used and significant efforts are underway by researchers worldwide to speed it up.
“A standard copper surface will kill about 97% of golden staph within four hours,” said Professor Ma Qian, a researcher in the School of Engineering at RMIT University.
“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.”
The copper’s unique porous structure was key to its effectiveness as a rapid bacteria killer.
Professor Qian and colleagues used a special copper mould casting process to arrange copper and manganese atoms into specific formations.
The manganese atoms were then removed from the alloy using a cheap and scalable chemical process called dealloying, 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 Dr. Jackson Leigh Smith, a researcher in the School of Engineering at RMIT University and CSIRO.
“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’s work was published in the journal Biomaterials.
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J.L. Smith et al. 2022. Robust bulk micro-nano hierarchical copper structures possessing exceptional bactericidal efficacy. Biomaterials 280: 121271; doi: 10.1016/j.biomaterials.2021.121271
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