Abstract
While nanoscale nipple arrays are expected to reduce light reflection and/or dust contamination in some insects, similar structures have been reported in various marine invertebrates. To evaluate the anti-contamination property of the structure in aquatic regimes, we measured the adsorption and adhesion forces on the flat surface and MOSMITE™ (Mitsubishi Chemical Corporation, Tokyo, Japan), a synthetic material mimicking the nipple array, under water. A small force toward the surface occurred when the probe approached the substrate surface. This adsorption force was significantly smaller on MOSMITE™ than on the flat surface. The adhesion force toward the surface occurred when the probe was detached from the surface, and it was also significantly smaller on MOSMITE™ than on the flat surface. The adhesion force in the air was much greater than the force under water, and the force was also significantly smaller on MOSMITE™ than on the flat surface. In the aquatic regime, the nipple array provides less adsorption/adhesion properties for the surface and thus, the organisms would have less contamination of microparticles on their body surface. As the adsorption and adhesion forces are also involved in the attachment of cells, tissue, and larvae, less adhesive body surfaces should be beneficial for survival in aquatic environments, as well as land environments.
Highlights
The Atomic Force Microscopy (AFM) images of the MOSMITETM surface measured under water and in the air were similar to each other (Figure 2a,b)
The height of the structure was much shorter with the colloidal probe under water showed that the MOSMITETM adsorbs less and in the AFM measurements (Figure 2c,d) than in the electron micrographs (Figure 1b,c) adheres less to the microparticles than the flat film, indicating the anti-contamination because the probe tip did not reach the bottom of the nipple array due to the high aspect property of the nipple array in the aquatic regime, as reported in the aerobic regime
The present study indicated that the nanoscale nipple array provides less adsorption and less adhesion to the surface in the aquatic regime and the organisms with the nipple array would be less contaminated with microparticles on their body surface than would those with a flat surface
Summary
Nanoscale nipple arrays (or ”moth-eye structures”) were originally reported from the cornea of the compound eyes of a night moth [6] and this surface structure forms a gradient of refractivity, resulting in the reduction in light reflection and the increase in light transmittance [6,7]. This structure can be regarded as a multifunctional structure; the nipple array on the cicada wing and the cornea of some insects was shown to reduce adhesion and water wettability and may serve anti-contamination and anti-wetting purposes, respectively [8,9]. Nanoscale nipple arrays and similar structures have been found in terrestrial insects as well as various invertebrate taxa inhabiting aquatic environments, such as annelids, echinoderms, sessile and pelagic tunicates, and endoparasitic copepods [12,13,14,15,16,17,18,19]
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