Bactericidal Activity of Superhydrophobic and Superhydrophilic Copper in Bacterial Dispersions

Abstract

A method based on nanosecond laser processing was used to design superhydrophilic and superhydrophobic copper substrates. Three different protocols were used to analyze the evolution of the bactericidal activity of the copper substrates with different wettability. Scanning electron microscopy was used to study the variation of cell morphology after the attachment to superhydrophilic and superhydrophobic surfaces. The dispersions of Escherichia coli K12 C600 and Klebsiella pneumoniae 811 in Luria Bertani broth in contact with the superhydrophilic copper surface showed enhanced bacterial inactivation, associated with toxic action of both hierarchically textured copper surface and high content of Cu2+ ions in the dispersion medium. In contrast, the bacterial dispersions in contact with the superhydrophobic copper substrates demonstrated an increase in cell concentration with time until the development of corrosion processes. The resistance of bacterial cells to contact the copper substrates is discussed on the basis of surface forces, determining the primary adhesion and of the protective action of a superhydrophobic state of the surface against electrochemical and biological corrosion.

Increasing Antibacterial Efficiency of Cu Surfaces by targeted Surface Functionalization via Ultrashort Pulsed Direct Laser Interference Patterning

“…Thereby it has to be questioned if the increase in antibacterial efficiency and Cu ion release on asprocessed surfaces might be affected by additional mechanical damaging of the bacteria by the flake-like oxidic sub-structure, like, for example, on Cicada and Dragonfly wing surfaces [32,33] and short pulsed laser treated Cu surfaces. [38,39] In order to investigate this more closely, scanning electron microscopy (SEM) imaging of formaldehyde-fixated bacteria after wet plating was conducted to get a hint on the dominant mode of action in bacteria killing on as-processed USP-DLIP surfaces. Since formaldehyde has a low pH value, bacteria fixation is accompanied by intense corrosive attack of the Cu surfaces, especially visible in the peak areas of USP-DLIP patterns, whereby this statement must be made primarily by observing the morphology of adhering bacteria.…”

“…[37] First approaches involving functional surface properties on antimicrobial copper surfaces highlighted the possibility to reduce bacterial transmission by hydrophobic wetting similar to the lotus effect. [18,19] In more recent studies, both Boinovich et al [38] and Selvamani et al [39] achieved antibacterial efficiency exceeding the copper-based reference material by the coupled effect of surface roughening and enhanced wettability induced by short pulsed laser treatment. Here, soaking of the deposited liquid into the porous surface structure forces the bacteria against the hierarchically scaled surface features resulting in structural cell membrane damage, [38][39][40] similar to the killing mechanism of bacteria piercing surface topographies on Cicada or Dragonfly wings.…”

“…[18,19] In more recent studies, both Boinovich et al [38] and Selvamani et al [39] achieved antibacterial efficiency exceeding the copper-based reference material by the coupled effect of surface roughening and enhanced wettability induced by short pulsed laser treatment. Here, soaking of the deposited liquid into the porous surface structure forces the bacteria against the hierarchically scaled surface features resulting in structural cell membrane damage, [38][39][40] similar to the killing mechanism of bacteria piercing surface topographies on Cicada or Dragonfly wings. [32,33] Unfortunately, antibacterial efficiency decreases strongly as soon as the surfaces stabilize at hydrophobic wetting, [38,41] which is most likely linked to the dense superficial layer of CuO initiated during short pulsed laser processing [42] showing reduced antimicrobial capacities due to reduced Cu ion release.…”

“…Here, soaking of the deposited liquid into the porous surface structure forces the bacteria against the hierarchically scaled surface features resulting in structural cell membrane damage, [38][39][40] similar to the killing mechanism of bacteria piercing surface topographies on Cicada or Dragonfly wings. [32,33] Unfortunately, antibacterial efficiency decreases strongly as soon as the surfaces stabilize at hydrophobic wetting, [38,41] which is most likely linked to the dense superficial layer of CuO initiated during short pulsed laser processing [42] showing reduced antimicrobial capacities due to reduced Cu ion release. [14] Therefore, it is important to include all functional aspects of their antiseptic effectiveness when specifically optimizing antimicrobial copper surfaces in order to maintain the positive effects over a longer period of time.…”

A novel methodology to study antimicrobial properties of high-touch surfaces used for indoor hygiene applications—A study on Cu metal

“…A variety of test methods have been suggested to inspect the antimicrobial efficacy of massive surfaces of Cu metal and Cu-based alloys [18,32,[42][43][44][45][46] at different relative humidities, temperatures, inoculum solutions, volume to surface area ratios, and microbial cultures etc [7]. Existing protocols are based on investigations in a nutrient broth ideal for the growth of bacteria [47] rather than in contact with human or synthetic sweat, as would be a more realistic case.…”