Thermal Spray Copper Alloy Coatings as Potent Biocidal and Virucidal Surfaces

Abstract

Microbial and viral pathogen contamination of touch surfaces contributes to the rapid transmission of diseases. It has been known for decades that microbes and viruses are rapidly inactivated when exposed to copper and its alloys. Consequently, the use of thermal spray technologies to coat surfaces in healthcare and public settings has been receiving a considerable amount of interest during recent viral pandemics and particularly now with COVID-19. This review is focused on recent successes using thermal spray technology to uniformly coat metal and organic surfaces, providing a rapid and economical means of inhibiting fomite transmission of pathogens on diverse surfaces with complex topographies. Emphasis is placed on the influence of lamella structure, porosity, and roughness of the coatings as it pertains to biocidal activity and the implications of using this knowledge to optimize the ability of copper coatings to irreversibly inactivate viral pathogens, regardless of their genomic mutation rates. Results of the long-term performance of the copper alloy coatings in real hospital settings in Canada and Peru are also presented.

Keywords: antibacterial coatings; copper/copper alloy coatings; thermal spray of copper-based coatings on wood and polymer; twin wire-arc spray coating.

Figure 1

Microstructure of a bulk copper (left) and a wire-arc-sprayed copper coating (right) with orientation of grains in a lamella (insert) [20]

Figure 2

Reduction in bacterial numbers after contact with different surfaces (a) S. aureus NCTC 11047, (b) E. coli NCTC 10418 [20]

Figure 3

SEM micrographs of the as-sprayed copper coating surface

Figure 4

Silver nanoparticles deposited onto the fabric fibers [32].

Figure 5

SEM images of bacteria on copper alloy coating. (a) Surface (Ra 3.5µm) with random orientation of bacteria in scratches, (b) bacteria deformation due to stress induced by exposure to copper [28].

Figure 6

Bacterial survival (a) E. coli and (b) S. epidermidis on copper alloy surfaces in comparison with stainless steel

Figure 7

Comparisons of B. subtilis endospore survival of stainless steel, copper alloy sheet, and thermal spray copper alloy on surfaces with roughness Ra = 3.5 μm [28]

Figure 8

B. subtilis endospores degradation and transformation into nanoflowers (1), a formed nanoflower after 7 days of exposure (2), inner structure of the nanoflower (FIB cross section) (3) [28]

Figure 9

The waiting room and coated armchairs in Toronto General Hospital (Canada)

Figure 10

Plates coated by CuNiZn alloy installed in a hospital nursing station (1), and samples receiving shelf (2) (Lima, Peru) and (3) coated doors hardware for installation in Mount Sinai Hospital (Toronto, Canada)

Figure 11

CFU counts during four weeks at different locations in the hospital (Lima, Peru)

Figure 12

Cross section of CuNiZn alloy coating on aluminum substrate. EDS analysis shows formation of oxide scale on the interface.

Figure 13

TWA copper coating adhesion (ASTM D4541) to mahogany (a), MDF (b), and adhesion values for different wood substrates (c).

Figure 14

Bare wood (left) and Cu-coated (right) samples after 12 weeks of decay test [47]