Antibacterial plastic surfaces by PVD sputter deposition

This work presents first results of a research project which aims to establish plasma surface treatment methods (PVD-HF sputtering) for the antibacterial functionalization of plastic surfaces. Sputter processes are used to deposit different thin metal/metal-oxide films on to the surface of a wide range of different polymers. The according biocidal effect is evaluated afterwards by combined microbiological analysis and fluorescence microscopy. In contrast to more traditional microbial inhibition methods (like addition of metal oxide micro- particles during the extrusion process), the presented approach tries to create metal-oxide based biocidal surface properties directly at the surface by means of plasma deposition. In particular, a HF-PVD plasma sputter system (13,56 MHz) is used to deposit the following metals/oxides: Zn, Ag, Cu, etc. In this way, substrate specific characteristics of a large number of different plastics (e.g. PLA, PA6, PP, PE, HDPE, PS, ABS, PMA) are investigated. The resulting physical surface properties are characterized by atomic force microscopy (AFM), electron microscopy (EDX), scratch tests, contact angle measurements etc. Special focus is also put on the surface pre-treatment (like cleaning and activation). The coated and uncoated surfaces are then microbiologically tested, i.e. the survival rates of bacteria strains (over a defined period of time) are determined by using a fluorescence spectroscopic assay. The investigated bacteria are Escherichia coli and Pseudomonas aeruginosa, two very typical representatives of pathogenes (e.g. for nosocomial infections). The survival rates are monitored by using the LIVE/DEAD BacLight Bacterial Viability Kit (Molecular Probes) in a commercial fluorescence microscope, which allows a relatively fast estimation of a potential antimicrobial effect. Additionally, standard microbiological tests (like ATP luminescence test, Alamar-Blue method and Agar diffusion test) are conducted for more precise results.