Putative Functions and Functional Efficiency of Ordered Cuticular Nanoarrays on Insect Wings

Abstract

The putative functions and functional efficiencies of periodic nanostructures 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 approximately 200 nm and may have multiple functionalities. Not only do the structures confer survival value by virtue of camouflage, but they may also serve as antiwetting 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 has been demonstrated using AFM as a nanomachining 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-40 microm. The particles can be removed from the array by forces in the range 2-20 nN; conversely, forces in the range 25-230 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 show that the wing represents a low-surface-energy membrane with antiwetting properties. The inference is that a combination of chemistry and structure constitutes a natural technology for conferring resistance to contamination.

Fouling of nanostructured insect cuticle: adhesion of natural and artificial contaminants

“…The arrays consist of hexagonally packed spherically capped conical protuberances with a spacing and height of *200 nm and radius of curvature of *25-45 nm at the apex. Similar features have been found on the wings of a number of other cicada species including Aleeta curvicosta, Tamasa tristigma, Macrotristria angularis, Psaltoda claripennis and Thopha saccata (eg Watson et al 2008). The features are present on all areas of the dorsal and ventral wing membrane.…”

“…A previous study has demonstrated the functional effectiveness of similar structures as an antireflective surface which presumably helps to camouflage the insect from predators (Watson et al 2008). The surfaces also demonstrated low adhesion with hydrophilic particles (Watson et al 2008). The multi-functional nature of the structures appears to be a common feature of the cuticle found on many insect species.…”

“…The features are present on all areas of the dorsal and ventral wing membrane. A previous study has demonstrated the functional effectiveness of similar structures as an antireflective surface which presumably helps to camouflage the insect from predators (Watson et al 2008). The surfaces also demonstrated low adhesion with hydrophilic particles (Watson et al 2008).…”

“…This provides strong evidence for specific dimensional structure size/shape for specific functionality on selected regions of the wings. Regions of the wing where the antireflection property is required have the necessary structure dimensions (less than the wavelength of light [Watson et al 2008]) while other coloured regions are not restricted by this wavelength condition. Suggested functioning of these structures on coloured regions is discussed below.…”

“…One of the most striking nanocomposite materials is the insect cuticle (Vincent and Wegst 2004). Recently micro-and nanostructures found on insect cuticles have been shown to exhibit a range of properties such as superhydrophobicity, directed wetting, ultra-low adhesion and self-cleaning (Parker and Lawrence 2001;Watson et al 2008Watson et al , 2010aWatson et al , 2011aHu et al 2011).…”