September_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 0 2 5 Two sets of strawberries, one placed on copper mesh and the other on plastic, both at room temperature. From top: (a) starting condition; (b) after 24 hours; and (c) after 43 hours. Note mold development on strawberry placed on plastic and its absence on strawberries placed on copper after 43 hours. Courtesy of Prof. Q.J. Wang. MATERIALS SCIENCE AND CORONAVIRUS SERIES ANTIMICROBIAL COPPER- CONTAINING STAINLESS STEELS SHOW PROMISE Given the demonstrated antimicrobial properties of copper, it is incumbent upon materials scientists to design potent antimicrobial copper-containing stainless steels as an economical option. Olivia Barber, Arman Khan, Erica M. Hartmann, Dieter Isheim, Semyon Vaynman, Q. Jane Wang, and Yip-Wah Chung, FASM* Northwestern University, Evanston, Illinois T ransmission of bacteria and virus- es through touched surfaces is an important public health concern, heightened recently by the COVID-19 pandemic. As discussed in a previous article in this series [1] , it has long been known that copper and copper-rich al- loys exhibit potent antimicrobial prop- erties. However, instead of copper, stainless steels are in widespread use in hospitals, medical facilities, and pub- lic transportation, despite their lack of antimicrobial properties. One reason is the lower cost of stainless steels. Anoth- er reason is corrosion resistance and ap- pearance. Stainless steel has a pleasing appearance and is more corrosion-re- sistant than Cu, which develops an un- appealing green or dark brown tarnish when corroded. Finally, stainless steels have higher yield strength (e.g., 250 MPa for stainless steel 304) than annealed Cu and Cu-rich alloys (70-170 MPa) and are therefore more suitable for applica- tions such as hospital beds and hand- holds used in public transportation. KILLING BACTERIA AND VIRUSES Bacteria range in size from 0.5 to 10 µm, whereas viruses are two orders of magnitude smaller, from about 5 to 300 nm. Bacteria come in many shapes such as spheres or rods depending period (incubation time), after which the remaining number of live microor- ganisms is determined. This number is *Member of ASM International on the species. All spe- cies have a cell mem- brane accompanied by an outer cell wall, which var- ies in sophistication. In contrast to bacteria, vi- ruses are surrounded by a protein capsid and sometimes have an addi- tional outer lipid envelope acquired from the host. Microorganisms including bacteria and viruses are of- ten sorbed to particulates or contained within aero- solized droplets in the en- vironment. When these droplets land on surfaces, rapid inactivation of the microorganisms contained therein would minimize transmission due to touch. To test a surface for antimicrobial properties, microbes are first adhered to the surface by direct application or immersion of the surface into a solu- tion containing a known concentration of micro- organisms [2] . The micro- organisms remain in contact with the sample at a given temperature (room temperature or 37°C) for a certain time (a) (b) (c)