Controlled bacterial interaction to increase the antimicrobial efficiency of copper surfaces

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The bacterial load on contact surfaces in public facilities such as hospitals can be reduced significantly by utilising antimicrobial copper alloys, which are lowering the spreading of infection diseases, particularly those caused by multi-resistant germs. The antimicrobial efficiency of copper containing surfaces is closely linked to their surface properties, which might have a beneficial or inhibitive effect on the bacterial killing.One objective of this project is to quantify the influence of the topographical and chemical properties of the surface on the antimicrobial efficiency of copper and its alloys. Why and how bacteria adhere to modified copper surface as well as how this is linked to the antimicrobial effect of the substrate needs to be thoroughly investigated. Laser-assisted surface processing enables the modulation of both surface topography and chemistry. By this, the purely electro-chemical bacteria killing mechanism is supplemented by topographical contact mechanic effects. Surface structures of similar scale as the bacteria are generated by Direct Laser Interference Patterning (DLIP) in order to selectively increase or reduce their contact area to the substrate. Using different pulse durations (10^-9 to 10^-15 s) provides the possibility to alter the surface chemistry due to varying laser/material interactions (ablation or melting) without significantly changing the produced surface topographies. The influence of this process on the wettability is quantitatively analysed using high-resolution microstructural and chemical characterisation and correlated to the bacterial killing efficiency of the surfaces. In order to achieve a better understanding of the interactions between the bacteria and the substrate, the adhesion of the germs on different modified surfaces is examined by recording force/distance curves using single-bacteria probes in AFM.Assessing the risk emanating from bacteria, which are developing resistances towards modified copper surfaces represents an additional objective of this study. Bacterial strains, which grew resistant to copper during the experiments, are tested for changes in their characteristic pathogenic properties like viability, proliferation and virulence. The examinations are also including the analysis of copper resistance mechanisms of isolated mutated strains by genome- and transcriptome essays. The knowledge gained about the connection of surface properties of copper alloys and their antimicrobial efficiency shall enable a more focused and efficient utilisation of these materials in antimicrobial applications.