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

Figures & data

Figure 1. Topographical SEM images of: (a) and (b) Cicadetta oldfieldi (top and cross-section, respectively) and, (c) and (d) black coloured region of Gudanga sp. nr adamsi (Black cicada) wing membrane (top and cross-section, respectively). (e) Structuring found on the dragonfly (Rhyothemis phyllis chloe) wing membrane. (f) Micron, and (g) sub-micron structures found on a moth wing (Prasinocyma albicosta). (h) and (i) Lacewing (Glenoleon pulchellus) and flower wasp (Scolia soror) nanostructures, respectively, and (j) broad bump structuring of the bladder cicada (Cystosoma schemltzi).

Table 1. Geometrical parameters of cuticle from insect species investigated in this study.

Type/Species	Height	Structure density (μm^−2)	Structure width (maximum)	Structure spacing/periodicity	Shape
Super hydrophobic cuticle
Cicada	200 nm	42	65 nm	200 nm	Spherically capped, conical
Cicadetta oldfieldi	SD 28 nm		SD 13 nm
Black cicada	Forewing – 1.5 μm	0.24	665 nm	2.1 μm	Diamond-like shape
Gudanga sp. nr adamsi	SD 0.19 μm		SD 65 nm
Dragonfly	350 nm	43	65 nm	150 nm	Rods
Rhyothemis phyllis chloe	SD 35 nm		SD 10 nm
Moth	Valley/peak dist. 500 nm	–	105 nm	Longitudinal ridge spacing – 1500 nm	Scales, longitudinal ridges, lateral crossbeams
Prasinocyma albicosta	SD 100 nm		SD 13 nm	Ridge width: Thin – 120 nm thick – 390 nm
Lacewing	950 nm	–	65 nm	–	Interconnected netting composed of ridges
Glenoleon pulchellus	SD 100 nm		SD 50 nm
Hydrophilic cuticle
Flower wasp	187 nm	2	0.47 μm	400 nm	Curved projections
Scolia soror	SD 18 nm		SD 0.09 μm
Bladder cicada	117 nm	1.6	306 nm	800 nm	Curved projections
Cystosoma schmeltzi	SD 34 nm	(1.4 ∼ 2.6)	SD 80 nm

Figure 2. (a) Graph displaying the species type as a function of the apparent contact angle (right axis) and adhesion (left axis). The adhesion measurements were obtained using three different particles (4.5 and 30 μm silica beads, and an AFM silica tip (ca 28 nm)). Error bars represent SEs. Photographs showing a 10 μl droplet deposited on (b) a cicada wing membrane, and (c) hydrophobic PDMS surface. (d) and (e) show the PDMS replica of the cicada Tosena sybilla and the interaction of a water droplet with a polymer (PDMS) replica of the cicada Gaeana cheni, respectively.

Figure 3. SEM images showing the orientation of the contaminating particulates attached to AFM levers. (a) Pimelea linifolia ssp., (b) Grevillea ‘Red Sunset’, (c) Acacia fimbriata, and (d) 30 μm silica bead.

Table 2. Dimensional parameters of all the particles used for adhesion measurements.

Tip/Microsphere supplier	Chemical composition	Actual diameter	Actual surface roughness (1x1 μm^2 area) RMS (nm)
NDT AFM tip	Silica	28 ± 6 nm	–
Bangs Laboratories. Cat no. SS05N	Silica	4.53 ± 0.05 μm	2.3 ± 0.2
Microspheres–Nanospheres Company Cat no. 147152-10	Silica	30.16 ± 0.17 μm	6.5 ± 0.3
Nova-Pak® C18. Cat. No WAT015220	C18	4.15 ± 0.06 μm	16.5 ± 2
Note: The values are averaged for 5 particles per particle type (35 in total). *Furrows – elongated/protruding structures on the pollen walls. **Pores – holes/valleys in the pollen walls.
Pollen type	Structure height (SD) (μm)	Structure density (μm^-2)	Structure width (SD) (μm)	Structure periodicity (μm)	Structure
Pimelea linifolia ssp.	0.397 (0.128)	0.225	0.32   (0.022)	2.11	Furrows*
	0.5    (0.074)	0.047	2.4     (0.45)	4.61	Flat furrows
Grevillea ‘Red Sunset’	0.66   (0.17)	0.79	0.99   (0.28)	1.13	Furrows
	–	1	0.355 (0.117)	1	Pores**
Acacia fimbriata (Golden wattle)	0.67   (0.19)	0.007	10.4     (1.56)	11.8	Frame shaped furrow
	0.67   (0.19)	0.007	2.47   (0.25)	11.8	Outer frame furrow
	0.67   (0.19)	0.007	5.75   (1.11)	11.8	Inner frame furrow
	0.67   (0.19)	0.007	0.63   (0.1)	11.8	Grooves
	0.18   (0.08)	1	0.55   (0.10)	1	Furrows
Note: The values are averaged for 5 particles per particle type (35 in total). *Furrows – elongated/protruding structures on the pollen walls. **Pores – holes/valleys in the pollen walls.

Figure 4. Graph displaying the relationship between the apparent contact angle and adhesion with the C₁₈ particles on the hydrophilic and super/hydrophobic insect wing surfaces. Error bars represent SEs.

Figure 5. Graph displaying the apparent contact angle and adhesion with the three different pollen particles – ⋄ Pimelea linifolia ssp., ▵ Grevillea ‘Red Sunset’ and ˆ Acacia fimbriata ‘Golden wattle’. Error bars represent SEs.

Figure S1. An optical microscope image of a water droplet resting on the wing membrane of a cicada revealing an apparent contact angle (CA) of ca 150° with the surface.

Figure S2. Top (a) and side (b) view, SEM images of a PDMS replica of the black cicada (Gudanga sp.).

Figure S3. Top and side SEM images of the coloured regions found on the cicada wings of Tosena sybilla ((a) and (b), respectively) and Gaeana cheni ((c) and (d), respectively).

Figure S4. A dehydrated (a) and ‘fresh’ (b) forewing of the bladder cicada, Cystosoma schmeltzi.

Figure S5. SEM images of the finer surface features of the three pollen surfaces used. (a) Pimelea linifolia ssp., (b) Gravillea ‘Red Sunset’ and (c) Acacia fimbriata.

Figure S6. AFM images of a silica bead, revealing the finer surface structures. (a) A topographical image, (b) a 3-d representation, and (c) an artificially shaded and leveled 3-d image showing the fine surface features. The imaging was performed with the bead attached to a lever and scanned over a calibration grid, ie reverse imaging.

Figure S7. A single representative f-d curve showing multiple ‘jumps’ on the retract curve (red) obtained on the moth wing (Prasinocyma albicosta). The approach curve (blue) shows a distinct snap-on feature (and a general downward trend) where the scales are presumably statically attracted to the surface of the Si bead.

Figure S8. The overlapping scale arrangement of the Prasinocyma albicosta moth wing.

Figure S9. A pollen grain found on the wing membrane of the hydrophilic flower wasp (Scolia soror).