A systematic approach towards biomimicry of nanopatterned cicada wings on titanium using electron beam lithography

The interaction of bacteria on nanopatterned surfaces has caught attention since the discovery of the bactericidal property of cicada wing surfaces. While many studies focused on the inspiration of such surfaces, nanolithography-based techniques are seldom used due to the difficulties in fabricating highly dense (number of pillars per unit area), geometrical nanostructured surfaces. Here we present a systematic modelling approach for optimising the electron beam lithography parameters in order to fabricate biomimicked nanopillars of varying patterned geometries. Monte Carlo simulation was applied to optimize the beam energy and pattern design prior to the experimental study. We optimized the processing parameters such as exposure factor, write field size, pitch, the different types and thicknesses of the PMMA resist used, and the shape of the feature (circle or a dot) for the fabrication of nanopillars to achieve the best lift-off with repeatable result. Our simulation and experimental results showed that a circle design with a voltage of 30 kV and 602 nm thickness of PMMA 495 A4 as base layers and 65 nm of PMMA 950 A2 as top layer achieves the best results. The antibacterial activity was also validated on the representative fabricated titanium nanopillar surface. The surface with a base diameter of 94.4 nm, spike diameter of 12.6 nm, height of 115.6 nm, density of 43/μm², aspect ratio of 2.16 and centre to centre distance of 165.8 nm was the optimum surface for antibacterial activity. Such a systematic design approach for fabrication of insect wing-mimicked closely packed nanopillars have not been investigated before which provides an excellent platform for biomedical Ti implants.