October_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 | O C T O B E R 2 0 1 7 2 2 H umans have used copper since the dawn of civilization, initially for its hardness and durability—as in tools, weapons, armor, and jewelry—but in the past century or so, more for its elec- trical and thermal conductivity. We also know from historic writings that copper was once used millennia ago for its anti- microbial effect. Long before Louis Pas- teur revealed the existence of bacteria, the ancient Egyptians were using copper in various forms to sterilize wounds and preserve drinking water, as recorded in the “Edwin Smith Papyrus.” Interest in copper’s medicinal value continued for generations, but ended abruptly in the 1930s when antibiotics were introduced. Now, prompted by the emergence of an- tibiotic-resistant bacteria, researchers are taking a fresh look at the 29th element in the fight against infectious disease. BEHIND THE REDISCOVERY The story of copper’s recent redis- covery begins in the early 1980s in the Hamot Medical Center in Erie, Pa. As part of their training, Hamot’s house- keeping and maintenance staffs were required to work with nursing students to collect and culture microorganisms throughout the hospital. Invariably, tar- nished brass doorknobs, although ap- pearing dirty and unsanitary, harbored almost no live bacteria, while their glistening stainless steel counterparts proved time and again to be heavily contaminated [1] . Fast forward to the 2006 publica- tion of a landmark study that quantified COPPER ALLOYS RESURFACE AS AN ANTIMICROBIAL FORCE Metals containing copper could soon be a mainstay in the war against antibiotic- resistant bacteria because they kill microorganisms on contact, work around the clock, are self-sanitizing, and require little if any outside help to remain effective. Harold T. Michels,* Copper Development Association, New York Corinne A. Michels, Queens College, Flushing, N.Y. *Member of ASM International the ability of copper alloys to kill meth- icillin-resistant Staphylococcus aureus , or MRSA, one of themost globally perva- sive hospital “super bugs” of our time [2] . The dramatic results, summarized in Fig. 1, clearly indicate that MRSA cannot survive on a copper-containing surface, dying off entirely in just 90 minutes on pure copper and in three hours on brass (80 wt% Cu−20 wt% Zn). Stainless steel, in contrast, seems to be a safe haven, exhibiting no antimicrobial effect at all. The small die-off observed in the MRSA colony is due to evaporation. In 2008, two years after the MRSA study and following an extended se- ries of additional tests, the U.S. Envi- ronmental Protection Agency (EPA) registered copper alloys as an antimi- criobial material and approved a num- ber of public health claims [3] related to copper’s ability to kill specific bacteria. One claim is particularly relevant from an application perspective, stating, “When cleaned regularly, antimicrobi- al copper alloy surfaces kill more than 99.9% of [one of the six EPA registered] bacteria within two hours, and continue The “Edwin Smith Papyrus,” the world’s oldest surviving surgical document, details the use of copper to sterilize wounds and preserve drinking water. Circa 1600 B.C.