Tailor the antibacterial efficiency of copper alloys by oxidation: when to and when not to

Abstract

Copper and its relevant species, such as oxides and many alloys, have been recognised as potential antibacterial surfaces. Despite the relatively low antibacterial efficacy of cuprous oxide (Cu2O) compared to pure copper, it is still worth consideration in some scenarios. Taking copper-nickel co-sputtered thin films with two copper contents (55 and 92 at.%) as examples, this work investigated the potential of oxidation in altering the antibacterial behaviour of copper alloy surfaces. By heat treatment at 200–250 °C for 20–24 h, a layer mainly composed of Cu2O was successfully fabricated on the top of the Cu-Ni alloys. Antibacterial efficiency against Escherichia coli in 1 h was obtained by the droplet method and further compared. The coupons with 92 at.% copper became less effective after oxidation: the reduction rate declines from 97.0 to 74.3%; whereas the coupons with 55 at.% copper showed a large increase after oxidation, rising from 15.0 to 66.8%. The experiments described herein reveal a promising concept of oxidation in enhancing the less effective copper alloy surfaces for antibacterial applications. Graphical abstract

Surface Modification of Brass via Ultrashort Pulsed Direct Laser Interference Patterning and Its Effect on Bacteria-Substrate Interaction

“…Proceeding with CuZn37 polished (black graph in Figure ), a fast reduction in CFU-value for the same exposure time but rather slower than that of pure copper is recorded. This is an expected result due to the lower concentration of copper, , which is confirmed by the attenuated Cu-ion release (Figure b). In the as-processed state (orange graph Figure ), a considerably reduced killing and corresponding copper-ion release rate are observed, which denotes an inadequate antibacterial activity, despite the increased and improved contact area.…”

“…First, depending on the oxidation state of pure copper, the release of Cu-ions is affected. 4 And second, the adhesion of bacterial droplets is impaired by the reduced wettability due to the topographical construct of the oxides but also due to the accumulation of carbon species during the aging process, i.e., carbon oxides, hydrocarbons, etc.…”

“…Apart from that, a layer of flake-like substructures is observed that indicates the formation of oxides consequent to laser processing, as also shown by Müller et al The presence of oxides plays a vital role in altering the crucial parameters of antibacterial properties, i.e., Cu-ion release on contact and the adhesion of bacteria. First, depending on the oxidation state of pure copper, the release of Cu-ions is affected . And second, the adhesion of bacterial droplets is impaired by the reduced wettability due to the topographical construct of the oxides but also due to the accumulation of carbon species during the aging process, i.e., carbon oxides, hydrocarbons, etc.…”

“…Metals like copper, copper alloys, cadmium, and silver have been the focus of investigation for their naturally occurring antibacterial properties. ,,,− Moreover, metal oxides like zinc oxide and titanium oxide, which show antibacterial activities upon exposure to ultraviolet light, are also being investigated. , In the case of pure copper, surface modification via ultrashort pulsed direct laser interference patterning (USP-DLIP) was shown to further improve the already pronounced inherent antibacterial properties. ,, This involves an increased Cu-sensitivity alongside improved bacterial contact conditions . The antimicrobial effect of Cu surface is directly related to the quantitative release of cytotoxic Cu-ions, which are known to deteriorate both bacteria and viruses by several modes of action, e.g., targeting the cell wall, proteins, and DNA. , Here, the presence of copper oxides can impact the antibacterial properties: excessive cupric oxide (CuO) was shown to reduce antibacterial efficiency, whereas, for predominant cuprous oxide (Cu 2 O) composition, it is improved …”

“…Rapidly increasing infectious diseases remain a major social problem, and the threat of antibiotic resistance is a significant concern . However, alternative strategies such as the use of antimicrobial surfaces offer a promising solution to effectively inhibit the growth and spread of harmful microorganisms. − Inspired by nature’s morphological blueprints, researchers are constantly investigating new techniques to harness their beneficial properties. ,, The nanopillars on cicada wings are a primary example of a naturally occurring antibacterial effect owing to the surface structures . On the contrary, the hydrophobic behavior of the Lotus leaf is a result of micro- and nanostructures as well as their surface chemistry, which gives them a self-cleaning function …”