High surface area copper for improved antibacterial activity

At RMIT University in Australia, a team of scientists has developed a copper alloy that can kill bacteria on its surface 100 times faster than normal copper. The researchers made the material from copper and manganese atoms and removed the manganese after the material was formed, resulting in a comb-like copper structure with a massively increased surface area. The development could help fight drug-resistant bacteria in healthcare facilities and could be useful in antimicrobial door handles and handrails, face masks, ventilators and ventilation systems.

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

Copper is naturally antibacterial, with copper ions having toxic effects in exposed bacterial cells. While this natural phenomenon is useful, it can be a bit slow for routine antimicrobial use and potentially take hours to kill bacteria on a surface. For frequently touched objects like doorknobs in a busy hospital corridor, this likely wouldn’t be fast enough to prevent the transmission of bacteria from one person to another.

“A standard copper surface kills about 97% of the golden staphylococci within four hours,” said Ma Qian, one of the developers of the new material, in a press release. “Incredibly, when we placed golden staphylococci on our specially designed copper surface, they destroyed more than 99.99% of the cells in just two minutes. So it’s not only more effective, it’s also 120 times faster. Our copper structure has proven to be remarkably potent for such a common material. “

The new copper alloy, magnified 2,000 times under a scanning electron microscope, shows its unique micro-comb structure.

To make the copper alloy, the researchers used a copper mold casting process and added both manganese and copper to the alloy. However, a low-cost chemical process called de-alloying helped them remove the manganese, leaving a porous copper structure. Compared to unmodified copper, not only is the surface area increased dramatically, but the material is hydrophilic and attracts bacteria in surface water and creates additional stress for them.

“Our copper is made up of comb-like micro-cavities and in each tooth of this comb structure there are much smaller cavities on the nanoscale; it has a huge active surface, ”said Jackson Leigh Smith, another researcher who was involved in the study. “The pattern also makes the surface super hydrophilic or water-loving, so that the water lies on it as a flat film and not as droplets. The hydrophilic effect means that bacterial cells have difficulty maintaining their shape as they are stretched by the surface nanostructure, while the porous pattern allows for faster release of copper ions. These combined effects not only lead to a structural breakdown of bacterial cells, which makes them more susceptible to the toxic copper ions, but also facilitates the uptake of copper ions into the bacterial cells. It is this combination of effects that leads to a greatly accelerated elimination of bacteria. “

The researchers hope that the copper alloy could form a very useful antimicrobial surface in a wide variety of healthcare facilities and devices, including ventilation systems, door handles, and even face masks.

Study in the journal Biomaterials: Robust, hierarchical micro-nano-copper structures with exceptional bactericidal effectiveness

Over: RMIT

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