Understanding the Antipathogenic Performance of Nanostructured and Conventional Copper Cold Spray Material Consolidations and Coated Surfaces

Abstract

The role of high strain rate and severe plastic deformation, microstructure, electrochemical behavior, surface chemistry and surface roughness were characterized for two copper cold spray material consolidations, which were produced from conventionally gas-atomized copper powder as well as spray-dried copper feedstock, during the course of this work. The motivation underpinning this work centers upon the development of a more robust understanding of the microstructural features and properties of the conventional copper and nanostructured copper coatings as they relate to antipathogenic contact killing and inactivation applications. Prior work has demonstrated greater antipathogenic efficacy with respect to the nanostructured coating versus the conventional coating. Thus, microstructural analysis was performed in order to establish differences between the two coatings that their respective pathogen kill rates could be attributed to. Results from advanced laser-induced projectile impact testing, X-ray diffraction, scanning electron microscopy, electron backscatter diffraction, scanning transmission microscopy, nanoindentation, energy-dispersive X-ray spectroscopy, nanoindentation, confocal microscopy, atomic force microscopy, linear polarization, X-ray photoelectron spectroscopy, electrochemical impedance spectroscopy and copper ion release assaying were performed during the course of this research.

Antimicrobial Copper Cold Spray Coatings and SARS-CoV-2 Surface Inactivation

“…Rather, they subsequently partnered with academic researchers (Sundberg et al) to demonstrate the way in which more rapid contact killing/inactivation rates can be achieved by utilizing a novel nanostructured spray-dried pure copper feedstock powder instead of the conventionally gas-atomized powder typically used in copper cold spray deposition 25 Thereafter, publications focusing on various material aspects such as surface roughness, surface species and surface chemistry, corrosion, and microstructure, were pursued by Sundberg et al [26][27][28][29][30] Around the same time, Champagne, Sundberg, and Helfritch, coauthored a more focused document that reformulated their respective mechanistic framework for interpreting the postulated reasons as to why antimicrobial copper cold spray coatings antipathogenic efficacies outperform many alternative surface engineering solutions 31 . Not long after, a holistic framework for understanding the antipathogenic performance unique to copper cold spray coatings was presented by Sousa et al 22 Beyond that time, Rutkowska-Gorczyca investigated the microstructure of an antibacterial copper and titanium dioxide composite coatings produced using low pressure cold spray in 32 . Sanpo et al analyzed a copper and zinc oxide composite cold sprayed coating for the purpose of contact killing and prohibiting C. marina bacterial attachment to maritime vessel surfaces 33 .…”

“…However, in 2019 and 2020, Sousa et al began to further analyse the microstructures of antipathogenic copper cold sprayed materials to investigate the suitability of Champagne et al's dislocation driven copper ion diffusion framework for assessing the increased contact killing/inactivation rates for both viral and microbial pathogens relative to non-cold spray materials/solutions. As a result, the most current assessment and research provides readers with a detailed look into the role such material defects, i.e., dislocations, maintain relative to the role of grain-boundary mediated copper ion diffusion 22 .…”

On the emergence of antibacterial and antiviral copper cold spray coatings

“…Said otherwise, Champagne et al conveyed dislocation density as the microstructural constituent most responsible for copper cold spray coatings’ antibacterial and antiviral behaviors. However, a 2020 article by Sousa et al gave an alternate microstructure-mediated mechanistic framework which classified the surface area concentration of polycrystalline grain boundaries of the consolidated coated material as being more telling of the surfaces’ antimicrobial behavior than dislocation density alone [ 17 ].…”

“…Rather than disregarding dislocation density when formulating a mathematical relation for the effective copper ion diffusivity, wherein the copper microstructure with the greatest effective copper ion diffusivity corresponds with the most antipathogenic crystal structure, Sousa et al discovered the fact “that the grain boundary contribution to the effective diffusivity of copper ions in the nanostructured material outperforms the diffusivity of dislocation pipe diffusion by an order of magnitude” [ 17 ], where Champagne et al presented the effective copper ion diffusivity as,…”

“…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 ] …”