May/June_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 | M A Y / J U N E 2 0 2 0 2 3 Fig. 2 — Bacterial levels found on brass and adjacent wood surfaces in Grand Central Terminal, New York City. bacterial killing occurred in a minute or less using this method. Samples of 50 microliters were used by van Dore- malen et al. [2] but no information on drying time, surface preparation, or sample distribution is provided. Prepa- ration of the metal surface can be a crit- ical factor. An insoluble organic coating, like benzotriazole, is typically present on copper sheet when it leaves the mill. This coating increases surface tension, and, thus, would inhibit inoculum dis- tribution, slow evaporation, and most likely inhibit copper ion release from the surface. These two factors, drying time of the inoculumand surface prepa- ration, are the most likely factors affect- ing the inactivation time. PROTECTING PUBLIC SPACES Small dry inoculums of infectious agents closely simulate what happens when a contaminated hand or a droplet from a cough or sneeze contacts a sur- face, making these results particularly relevant to the spread of disease in pub- lic spaces. Copper alloy inactivation is not limited to coronaviruses and works on viruses with different structures. Re- ports from the Keevil laboratory have shown that copper alloys inactivate murine norovirus [6] and Influenza A vi- rus [7] . As in their Hu-CoV-229E study, the rate of norovirus inactivation was found to be inversely correlated with copper concentration in both the cop- per-nickel and copper-zinc alloys, the common theme in all of the studies of antimicrobial copper alloy surfaces. Longevity of the antimicrobial ac- tivity of copper alloys is another very important consideration when select- ing materials for components for de- ployment in public spaces. This is really a three-part question: How long will the copper alloy maintain its ability to kill/ inactivate a disease organism; will dis- ease organisms become resistant to killing/inactivation by copper alloys; and what type of maintenance/clean- ing is required? Antimicrobial activity of copper alloys appears to be long-last- ing. The brass and adjacent wood sur- faces in Grand Central Terminal in New York City were used to answer this question. This beautiful Beaux-Arts building is lavishly decorated with mar- ble and brass, an antimicrobial alloy, and opened to the public over a century ago. Defined areas were sampled with a sterile cotton swab and the total num- ber of bacteria picked up by the swab determined. No information was col- lected on the cleaning history of the sur- face sampled or frequency of touching. The results are shown in Fig. 2. Bacte- rial count is expressed in CFU/100 cm 2 , or colony forming units per 100 square centimeters. The brass surfaces, with 88 and 51 CFU/100 cm 2 , had a significant- ly lower bacteria count relative to the adjacent wood, with 563 and 1866 CFU/ 100 cm 2 . This finding confirms that the brass components have retained anti- microbial capabilities after decades of hand touching. Viral inactivation by copper alloys has been largely unstudied but the re- ports mentioned here show the rapid irreversible destruction of viral parti- cles [3,6,7] . Since viral structure, of neces- sity, is largely constant, resistance is unlikely to be an issue. In the case of bacteria, the simplest mechanism of killing that is consistent with the data is the Membrane Target theory [4] . In this theory, an essential component of the bacterial membrane, unsaturated fat- ty acids, are modified by exposure to Cu+/Cu++ ions in a manner that caus- es complete loss of membrane integ- rity and cell rupture. Resistance to copper alloy surface exposure has not been found in the over tens of trillions of bacteria tested in laboratory studies. Thus, at least for bacteria, the heritable change required for resistance is highly improbable or lethal, making the organ- ism inviable [1,4] . Cleaning and maintenance are an- other important consideration. Most of the antimicrobial copper alloys that have U.S. Environmental Protection Agency (EPA) approval tarnish to some degree, but some are tarnish resistant, making them more useful for inclu- sion in public spaces. The Antimicrobial Copper Action Network website is a re- source where one can read the EPA-ap- proved cleaning protocols (amcopper. com) and obtain information about commercially available antimicrobial copper components. It is important to note that the EPA required exten- sive independent third-party laborato- ry testing, as described by Michels and Anderson [8] . The testing results demon- strate that the antimicrobial response of copper is powerful and enduring. RECOMMENDATIONS Everywhere we go we touch sur- faces that are likely to be contaminated with bacteria, viruses, and other dis- ease-causing microorganisms. Think about the last time you were in an air- port, a shopping center, or a hospital. You touched doorknobs, push plates, handles, stair railings, shopping cart handles, restroom faucets, and more. Any one of these surfaces in any of these public environments has the po- tential to transmit disease-causing mi- crobes to your hands that could result in an infection. Your first line of defense is frequent hand washing, but, what if these common touch surfaces were an antimicrobial copper alloy? They would be working all day, every day of the year to kill the bacteria, viruses, and fungi that cause infectious disease. Over 500 alloys have been approved by the EPA