Abstract
This study was focused on the biocidal efficacy on spores of copper alloy sheet and copper alloy coating at two different surface topographies. Endospores can remain viable in a dormant state for centuries. Our work compares the effectiveness of copper alloy coating and copper sheet metal in killing endospores. A twin-wire arc spray system was used for coating of stainless steel coupons. The feedstock was CuNiZn wire, the coating thickness was 400 µm. The copper alloy sheet metal had the same composition and is registered as antimicrobial by Environmental Protection Agency (US). Uncoated stainless steel coupons were used as controls in all experiments. The surface was polished to two roughness levels: Ra=3.5 µm and Ra=0.1 µm. The surface topography was analyzed by a stylus profilometer and 3D image analysis. EDS and FIB were used to characterize the elemental composition and structure of flower-like nanostructures and endospores. The results obtained in this study indicated that changes in Ra values of 0.1 and 3.5 µm had no significant impact on the biocidal activity of sheet metal and the coating on E. coli, S. epidermidis and B. subtilis. The coating was as effective as the EPA-certified sheet metal in the destruction of vegetative cells within 5 minutes. This study indicates that degradation of B. subtilis endospore begins within 2 hours after exposure to the coating. By day seven, only extensively degraded endospores and nanostructures were visible on both surfaces. Our results show that thermal spray copper alloy coatings were as effective as certified antimicrobial sheet metal in the destruction of endospores within hours; however, the coating was more effective in killing the endospores after one week of exposure.
