Direct laser interference patterning of stainless steel by ultrashort pulses for antibacterial surfaces

Direct Laser Interference Patterning (DLIP) with ultrashort pulses was exploited to produce tailored periodic sub-micrometer structures on stainless steel surfaces to reduce bacterial attachment and retention. Laser pulses with wavelength 1030 nm and duration 8 ps were employed to form a two-beam line interference pattern that was applied in a two-pass strategy to produce fine cross-wise surface structures with a period of similar to 850 nm and a depth of similar to 500 nm. The laser setup and process parameters were selected based on a simple theoretical model of the resulting interference pattern and ablation depth to limit the number of contact points available for bacterial cells with dimensions 500-2000 nm. Periodic 'cones' and 'holes' were produced covering areas of 250 mm(2) with the same interference pattern by exploiting the dependence of laser-induced periodic surface structures on polarization. Cones and holes yielded reductions in E. coli retention of 99.8% and 99.4%, respectively, and S. aureus retention of 70.6% and 79.1%, respectively, after two hours immersion in bacterial solution compared to reference samples. Such reductions achieved over large surface areas suggests that this approach is appropriate for upscaling and high throughput production of antibacterial metallic surfaces in the food and healthcare industries.