At RMIT University in Australia a team of scientists developed a copper alloy that can kill bacteria on its surface 100 times faster than regular copper. The researchers created the material using copper and manganese atoms, and then removed the manganese after the material was formed, resulting in a comb-like copper structure with massively increased surface area. The development could help with the fight against drug-resistant bacteria in healthcare facilities and may be useful in anti-microbial door handles and hand-rails, face masks, respirators, and ventilation systems.
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.
Copper is naturally antibacterial, with copper ions producing toxic effects in exposed bacterial cells. While this natural phenomenon is useful, it can be a little slow for routine antimicrobial use, potentially taking hours to kill bacteria on a surface. For commonly touched objects, such as door handles in a busy hospital corridor, this likely wouldn’t be fast enough to prevent bacterial transfer from one person to another.
“A standard copper surface will kill about 97% of golden staph within four hours,” said Ma Qian, one of the developers of the new material, in a press release. “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. Our copper structure has shown itself to be remarkably potent for such a common material.”
The new copper alloy, magnified 2,000 times under a scanning electron microscope, showing its unique micro-comb structure.
To create the copper alloy, the researchers used a copper mold casting process, and incorporated both manganese and copper into the alloy. However, an inexpensive chemical process called dealloying helped them to remove the manganese, leaving a porous copper structure. Not only is the surface area dramatically increased compared with unmodified copper, but the material is hydrophilic and draws bacteria in surface water into it and creates additional stress for them.
“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 Jackson Leigh Smith, another researcher involved in the study. “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 researchers hope that the copper alloy could make a very useful antimicrobial surface in a variety of healthcare settings and devices, including ventilation systems, door handles and even face masks.
Study in journal Biomaterials: Robust bulk micro-nano hierarchical copper structures possessing exceptional bactericidal efficacy