Silver/copper-mixed layers as antimicrobial surface coating

Over the last years, research in the areas of hygiene and healthcare has focused on the resurgence of antimicrobial coatings to prevent infections and control their spreading. We used a physical vapor deposition technology to deposit coatings of either silver or copper individually or as mixtures on polymeric substrates. Five combinations of silver and copper coatings were produced with a thickness of 50 nm. The amounts of silver and copper on the coated surfaces were determined using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX). The antimicrobial characteristics of silver and copper against Escherichia coli K12 (E. coli) were investigated, focusing on the possible synergistic effects of the two metals. The deposited coatings showed homogeneous mixtures of silver and copper clusters. The mixtures of silver and copper as well as pure silver showed antimicrobial properties. In contrast, pure copper did not exhibit any antimicrobial effects. Dissolution behavior of copper and silver was determined by incubation of mixed layers in physiological media (synthetic sweat). Copper coatings proved to be fully dissolvable whereas silver showed lower solubility. With increasing copper content in the mixed coatings, the dissolution of silver increased as well.