Putative functions and functional efficiency of ordered cuticular nanoarrays on insect wings

Abstract

The putative function(s) and functional efficiencies of periodic nano-structures on the surface of cicada wings have been investigated by atomic force microscopy (AFM) used as a tool for imaging, manipulation and probing of adhesion. The structures consist of hexagonal close-packed protrusions with a lateral spacing of ca. 200 nm and may have multiple functionality's. Not only do the structures confer survival value by virtue of camouflage, but they may also serve as anti-wetting and self-cleaning surfaces, and thus be resistant to contamination. These effects have been demonstrated by exposure to white light, liquid droplets and AFM adhesion measurements. The dependence of optical reflectivity and surface adhesion on surface topography have been demonstrated by using AFM as a nano-machining tool, as well as an imaging and force - sensing probe. The intact arrays display exceptionally low adhesion for particles in the size range 20 nm to 40 microns. The particles can be removed from the array by forces in the range 2 to 20 nN; conversely forces in the range 25 to 230 nN are required to remove identical particles from a flat hydrophilic surface (i.e., polished Si). Measurements of contact angles for several liquids and particle adhesion studies shows the wing represents a low surface energy membrane with anti-wetting properties. The inference is that a combination of chemistry and structure constitutes a natural technology for conferring resistance to contamination.