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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 | M A Y / J U N E 2 0 2 0 2 2 (b) (c) (a) (d) significant loss in infectious viral par- ticles, while C110 (100% Cu) and C210 (95% Cu) showed the fastest reduction, followed by increasing time for com- plete inactivation in the following order: C210 (95% Cu), C220 (90% Cu), C230 (85% Cu), C260 (70% Cu), and C280 (60% Cu). Note the inverse correla- tion between decreasing copper content and increasing time for inac- tivation in brass. Figure 1b is a plot of the data from the first 30 minutes of Fig. 1a. It shows a gradual decline, fol- lowed by rapid inactivation. Figure 1c shows a series of copper-nickel alloys ranging from 70%Cu to 90%Cu, N022 (100% Ni), and S304. N022 and S304 showed no significant loss in virus parti- cles. The copper-nickel alloys displayed increasing complete inactivation time with decreasing copper content in the following order: C110 (100% Cu), C706 (90%), C725 (88% Cu), C710 (80% Cu), and C715 (70% Cu). Again, note the in- verse correlation between decreasing copper content and increasing time for inactivation in copper-nickel al- loys. In Fig. 1d, a very small amount of inoculum, which dried immediate- ly, was placed on the metal samples to simulate a finger touch of the surface. Inactivation of Hu-CoV-229E was com- plete in 2.5 minutes on C110 (100% Cu) and 5 minutes on cartridge brass C260 (70% Cu) while S304 stainless steel dis- played only a modest reduction, most likely due to evaporation. These results strongly support the conclusions that copper alloys rapidly inactivate Hu-CoV- 229E virus and that the copper in the al- loy is responsible for the inactivation. These two articles [2-3] used differ- ent strains of coronavirus but this is un- likely to be the source of the observed differences in inactivation times. The anti-coronavirus activity of copper al- loys probably extends to all strains of coronavirus because this class of vi- rus is essentially structurally identical. We have all become familiar with the spherical shape of coronavirus with its protruding spikes. The virus’ RNA (its hereditary information) is contained inside a spherical “envelope” that pro- tects the RNA. The envelope is a thin sphere of lipid molecules (fatty acids) arranged in a double layer or a lipid bi- layer. Embedded within this lipid bilay- er are two viral proteins, E and M. A third protein, S, or spike protein, is anchored at one end into the lipid layer and proj- ects outward from the surface as radial spikes. These spikes give this group of viruses their name because they look like a “corona” when viewed at high magnification. Minor variations in the hereditary information (RNA) produce slight vari- ations in the proteins exposed at the outer surface. These proteins, particu- larly S, are responsible for attaching to and gaining entrance into respiratory cells where the RNA uses the metabol- ic machinery of the host cell to produce more viruses. Variations in these pro- teins do not produce significant vari- ation in the overall structure and function of the virus. Thus, one can sur- mise with a reasonable degree of confi- dence that the efficacy of copper alloys against Hu-CoV-229E should also be observed when tested with the newly emerged SARS-CoV-2 and SARS-CoV-1, the causative agent in the SARS epi- demic of 2003. Scientists believe that the differ- ences in exposure times observed by van Doremalen et al. [2] and Warnes et al. [3] result from technical differences in the experimental protocols and not from inherent differences among the vi- ral strains. Figure 1d demonstrates that small sample sizes, in this case 1 micro- liter or 1/50th of a drop, were inactivat- ed in 5 minutes or less. Similar results from a variety of laboratories studying copper alloy killing of bacteria found quite clearly that the volume of the in- oculum placed onto the metal coupon contributes significantly to the speed of inactivation. Killing was very slow during the time the sample was dry- ing on the surface but, once it dried, a precipitous decrease in the number of survivors was observed [4] . Another lab- oratory developed a “dry” technique of applying bacteria to the coupon with a cotton swab [5] . They found complete Fig. 1 — Inactivation of Human Coronavirus 229E by copper-zinc and copper-nickel alloys. Reproduced with permission fromWarnes et al., 2015 [3] .