On the emergence of antibacterial and antiviral copper cold spray coatings

Abstract

In this literature review, the antipathogenic properties and contact-mediated antibacterial and antiviral performance of copper cold spray surfaces are assessed and compared with alternative antimicrobial materials that are able to kill and/or inactivate infectious agents via direct contact. Discussion is also provided concerning the suitability of copper cold spray material consolidations as biocidal and viricidal surfaces that retain long-term functionality as a preventative measure against fomite transmission of pathogenic agents and hospital-acquired infections from contaminated high-touch surfaces. Numerable alternative antimicrobial coatings and surfaces that do not rely upon the oligodynamic action of copper are detailed. Given the ongoing need for recognition of said alternative antimicrobial materials by authoritative agencies, such as the U.S. Environmental Protection Agency, the relevant literature on non-copper-based antipathogenic coatings and surfaces are then described. Furthermore, a wide-ranging take on antipathogenic copper cold spray coatings are provided and consideration is given to the distinctive grain-boundary mediated copper ion diffusion pathways found in optimizable, highly deformed, copper cold spray material consolidations that enable pathogen inactivation on surfaces from direct contact. To conclude this literature review, analysis of how copper cold spray coatings can be employed as a preventative measure against COVID-19 was also presented in light of on-going debates surrounding SARS-CoV-2's non-primary, but non-negligible, secondary transmission pathway, and also presented in conjunction with the inevitability that future pathogens, which will be responsible for forthcoming global pandemics, may spread even more readily via fomite pathways too.

Keywords: Antimicrobial surfaces; Antipathogenic mechanisms; Atomic ion diffusion pathways; Biocidal contact killing; Biomaterials; Cold spray; Copper; Microstructures; Viricidal contact inactivation.

Fig. 1

Schematic of the copper cold spray process (a). The nanostructured spray-dried agglomerated copper feedstock utilized to produce an antimicrobial cold spray coating is shown in (b), while (c) presents a single particulate, d presents a cross-section of a single particle, and (e) is a cross-section of the resultant coating

Fig. 2

Resultant microstructures of each of the coatings procured and was adopted from the open source publication cited herein as reference [6]

Fig. 3

Copper release rate as a function of time, as well as the survival of E. coli (strain K12) inoculated upon various copper surfaces with observable differences in surface roughness and topographies [12]

Fig. 4

Adopted from [16] to highlight “Percent… MRSA… surviving after a two-hour exposure to copper surfaces”

Fig. 5

Multiscale area and complexity characterizations (ASME B46.1, ISO 25178-2) of topographies measured with AFM and confocal microscopy. MRSA (bacteria) and influenza A (virus) sizes given for size-scale reference [17]

Fig. 6

Taken from Santo et al. to demonstrate “Staphylococcus haemolyticus is rapidly killed on dry metallic copper (Cu) surfaces and cells accumulate large amounts of Cu. Cells of S. haemolyticus were exposed to dry metallic Cu surfaces or stainless steel for the indicated times, removed, washed, and plated on solidified growth media”

Fig. 7

Unique microstructure associated with nanostructured copper cold spray coatings studied by Sousa et al. [17]. Note that the embedded use of “GB” refers to grain boundaries and the embedded us of “D” refers to dislocations or dislocation structures

Fig. 8

“Transmission pathways for SARS-CoV-2 and behaviors needed to block these. The arrows to the left of the blue bar relate to the infected person while those to the right relate to other people who may become infected,” [50, 51].