Understanding the antibacterial mechanism of metal surfaces

Abstract

Bacterial inactivation on antibacterial metal surfaces has been widely used in medicine and daily life to inhibit infection caused by surface contact. However, the underlying antibacterial mechanism of metal surfaces has remained elusive due to a lack of comprehensive theoretical perspectives and direct evidence. Here, we propose a universal understanding of the bacteria-inactivation mechanism of metal surfaces and reveal the changes in bacterial survival behavior with time and spatial location. In terms of bacterial survival over time, we established a quantitative ion influx model and predicted four bacterial survival behaviors based on osmotic pressure changes and ion release. To demonstrate the spatial distribution of bacterial survival, we consider variations in metal antibacterial properties and electrode potentials and design five corrosion galvanic couples to cover all possible metal combinations. The results on the bacterial survival behavior over time confirm our theoretical predictions, exhibiting a dependence of bacterial viability on environmental humidity and metal toxicity. In addition, on the surfaces of galvanic couples, bacteria will experience the most pronounced decrease in viability at anodes, irrespective of the location of the antibacterial metals. This abnormal distribution pattern can be fundamentally attributed to the highest toxic-ion concentration resulting from a low pH at anodes. The consistency between our predictions and observed bacterial survival rates supports the notion that the antibacterial mechanism follows surface ion release and subsequent free-ion influx into the cytoplasm, leading to lethal biochemical reactions in bacteria. Statement of significance: Numerous studies have been conducted on developing antibacterial metals, alloys, and their related applications. However, the underlying antibacterial mechanism of metal surfaces has remained elusive. This work is the first to propose a general understanding of the antibacterial mechanism of metal surfaces, including the temporal and spatial characteristics of bacterial survival behavior. By building a theoretical model, we predicted and confirmed the shapes of the four bacterial survival curves over time. In addition, we found that bacteria have the worst viability loss at the alloy anode, even if non-antibacterial metals occupy this position. The conclusions can provide theoretical support for the antibacterial behavior of metal surfaces, including but not limited to Ag, Cu, Zn, and their corresponding alloys.