Copper is used to combat various strains of bacteria because the ions released from the surface of the metal are toxic to the bacterial cells. However, this process is slow. It takes about four hours for 97 % of Staphylococcus aureus (S. aureus) bacteria cells to be killed. Ma Qian, RMIT University, Melbourne, Victoria, Australia, and colleagues have designed and fabricated a robust bulk super hydrophilic micro-nano Cu structure which destroys more than 99.99 % of S. aureus bacteria in just two minutes.
A special copper molding process was used to produce an alloy in which copper and manganese atoms are arranged in specific formations. The team then used chemical dealloying, which refers to the selective removal of metal atoms by a corrosive medium, layer by layer, to dissolve the manganese atoms out of the alloy. This results in pure copper with tiny micro- and nano-scale voids on the surface. The copper structure is made up of comb-like microscale cavities. Within each tooth of this structure, there are much smaller nanoscale cavities. By this, a huge active surface is created. This pattern also makes the surface super hydrophilic, so that water lies on top of it as a flat film rather than as droplets.
Bacterial cells struggle to maintain their shape. They are stretched by the nanostructure of the surface. In addition, the porous pattern enables Cu ions to be released more quickly. The combination of these effects leads to structural degradation of the bacterial cells, making them more susceptible to the toxic Cu ions, and facilitates the uptake of Cu ions into the bacterial cells.
In addition, the team demonstrated the scalability of this technology on 2000 mm2 Cu disks. The researchers believe that their new material can be used as a low-cost antibiotic-free fast bactericidal material, for example, for antimicrobial door handles and other contact surfaces in schools, hospitals, homes, and public transport as well as for filters in antimicrobial respirators or ventilation systems, and in face masks. The team will now test it also with SARS-CoV-2 viruses.
- Robust bulk micro-nano hierarchical copper structures possessing exceptional bactericidal efficacy,
J. L. Smith, N. Tran, T. Song, D. Liang, M. Qian,
Biomaterials 2022, 280.