Influence of cuticle nanostructuring on the wetting behaviour/states on cicada wings

The nanoscale protrusions of different morphologies on wing surfaces of four cicada species were examined under an environmental scanning electron microscope (ESEM). The water contact angles (CAs) of the wing surfaces were measured along with droplet adhesion values using a high-sensitivity microelectromechanical balance system. The water CA and adhesive force measurements obtained were found to relate to the nanostructuring differences of the four species. The adhesive forces in combination with the Cassie-Baxter and Wenzel approximations were used to predict wetting states of the insect wing cuticles. The more disordered and inhomogeneous surface of the species Leptopsalta bifuscata demonstrated a Wenzel type wetting state or an intermediate state of spreading and imbibition with a CA of 81.3° and high adhesive force of 149.5 μN. Three other species (Cryptotympana atrata, Meimuna opalifer and Aola bindusara) exhibited nanostructuring of the form of conically shaped protrusions, which were spherically capped. These surfaces presented a range of high adhesional values; however, the CAs were highly hydrophobic (C. atrata and A. bindusara) and in some cases close to superhydrophobic (M. opalifer). The wetting states of A. bindusara, C. atrata and M. opalifer (based on adhesion and CAs) are most likely represented by the transitional region between the Cassie-Baxter and Wenzel approximations to varying degrees.     

Effects of Methanol on Wettability of the Non-Smooth Surface on Butterfly Wing

The contact angles of distilled water and methanol solution on the wings of butterflies were determined by a visual contact angle measuring system. The scale structures of the wings were observed using scanning electron microscopy, The influence of the scale micro- and ultra-structure on the wettability was investigated. Results show that the contact angle of distilled water on the wing surfaces varies from 134.0° to 159.2°. High hydrophobicity is found in six species with contact angles greater than 150°. The wing surfaces of some species are not only hydrophobic but also resist the wetting by methanol solution with 55% concentration. Only two species in Parnassius can not resist the wetting because the micro-structure （spindle-like shape） and ultra-structure （pinnule-like shape） of the wing scales are remarkably different from that of other species. The concentration of methanol solution for the occurrence of spreading/wetting on the wing surfaces of different species varies from 70% to 95%. After wetting by methanol solution for 10 min, the distilled water contact angle on the wing surface increases by 0.8°-2.1°, showing the promotion of capacity against wetting by distilled water.     

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

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 ∼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 μm. 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 adhesional properties of contaminating particles of scales of various lengths were investigated for a wide range of micro- and nanostructured insect wing cuticles. The contaminating particles consisted of artificial hydrophilic (silica) and spherical hydrophobic (C(18)) particles, and natural pollen grains. Insect wing cuticle architectures with an open micro-/nanostructure framework demonstrated topographies for minimising solid-solid and solid-liquid contact areas. Such structuring of the wing membranes allows for a variety of removal mechanisms to contend with particle contact, such as wind and self-cleaning droplet interactions. Cuticles exhibiting high contact angles showed considerably lower particle adhesional forces than more hydrophilic insect surfaces. Values as low as 3 nN were recorded in air for silica of ~28 nm in diameter and <25 nN for silica particles 30 μm in diameter. A similar adhesional trend was also observed for contact with pollen particles.     

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

The adhesional properties of contaminating particles of scales of various lengths were investigated for a wide range of micro- and nanostructured insect wing cuticles. The contaminating particles consisted of artificial hydrophilic (silica) and spherical hydrophobic (C₁₈) particles, and natural pollen grains. Insect wing cuticle architectures with an open micro-/nanostructure framework demonstrated topographies for minimising solid–solid and solid–liquid contact areas. Such structuring of the wing membranes allows for a variety of removal mechanisms to contend with particle contact, such as wind and self-cleaning droplet interactions. Cuticles exhibiting high contact angles showed considerably lower particle adhesional forces than more hydrophilic insect surfaces. Values as low as 3 nN were recorded in air for silica of ～28 nm in diameter and <25 nN for silica particles 30 μm in diameter. A similar adhesional trend was also observed for contact with pollen particles.     

Wing colors of Chrysozephyrus butterflies (Lepidoptera; Lycaenidae): ultraviolet reflection by males

Wing colors of the four species of Chrysozephyrus butterflies were analyzed by a spectrophotometer. As the dorsal wing surface of males showed a strong reflectance when the specimen was tilted, measurements were made by the tilting method. The dorsal wing surface of males which appears green to the human eye reflected UV (315-350 nm) as well as green light (530-550 nm). The reflectance rate of UV to visible green light varied among species with a higher rate for C. hisamatsusanus and C. ataxus, and a lower rate for C. smaragdinus and C. brillantinus. The peak wavelength and the peak height did not shift when the specimen was exposed to direct sunlight at least for 16 hr. Artificial removal of scales by scratching the wing surface decreased reflectance. Blue marks on the forewings of C. brillantinus, C. hisamatsusanus and C. ataxus females reflected UV to visible light of short wavelength, and orange marks on the dorsal surface of the forewing and the ventral surface of the hindwing of C. samaragdinus females showed a higher reflectance at longer wavelengths.     

Wettability of biomimetic thermally grown aluminum oxide coatings

In this paper, wettability behavior of a rough but intrinsically hydrophilic oxide ceramic, formed via simple thermal oxidation of a commercial metallic alloy in laboratory air, has been analyzed. Drop shape analysis (DSA) revealed static water contact angles for the rough ceramic surfaces up to 128° (greater than for Teflon?). We propose the high apparent contact angles to be a result of surface roughening via the morphological changes of the oxide scale with oxidation conditions. The surface morphological changes occurring during the growth of the oxide film resulted in the formation of vertical platelets that ably shifted the wetting behavior from a Wenzel to an unstable Cassie-Baxter state. The platelet morphology of the ceramic resembles the structure of epicuticular waxes on certain species of superhydrophobic leaves. Moreover, surface textures for very short oxidation times were also found to increase hydrophilicity in the scale and reduce the contact angle by imparting a Wenzel state. Various characterization techniques (XRD, XPS, and SEM) were performed in order to detect the crystallographic phases in the scales, analyze carbon content and determine the morphology of the oxide layer. Morphological features of the oxide platelets were quantified and platelet width, spacing and height were found to correlate well with the apparent contact angle trend as a function of oxidation time.     

Visual pigments, cone oil droplets and ocular media in four species of estrildid finch

A microspectrophotometric study was conducted on the retinal photoreceptors of four species of bird: cut-throat finches (Amadina fasciata), gouldian finches (Erythrura gouldiae), white-headed munias (Lonchura maja) and plum-headed finches (Neochmia modesta). Spectral characteristics of the photoreceptors in all four species were very similar. Rods contained a medium-wavelength-sensitive visual pigment with a wavelength of maximum absorbance at 502-504 nm. Four spectrally distinct types of single cone contained a visual pigment with wavelength of maximum absorbance at either 370-373 nm (ultraviolet-sensitive), 440-447 nm (short-wavelength-sensitive); 500 nm (medium-wavelength-sensitive) or 562-565 nm (long-wavelength-sensitive). Oil droplets in the ultraviolet-sensitive single cones showed no detectable absorption between 330 nm and 800 nm. Oil droplets in the short-, medium-, and long-wavelength-sensitive single cones had cut-off wavelengths at 415-423 nm, 510-520 nm and 567-575 nm, respectively. Double cones contained the visual pigment with wavelength of maximum absorbance at 562-565 nm observed in long-wavelength-sensitive single cones. Only the principal member of the double cone pair contained an oil droplet (P-type, cut-off wavelength at 414-489 nm depending on species and retinal location). Spectral transmittance of the intact ocular media of each species was measured along the optic axis. Wavelengths of 0.5 transmittance for all species were very similar (316-318 nm).     

Biophysical Model of Bacterial Cell Interactions with Nanopatterned Cicada Wing Surfaces

The nanopattern on the surface of Clanger cicada (Psaltoda claripennis) wings represents the first example of a new class of biomaterials that can kill bacteria on contact based solely on their physical surface structure. The wings provide a model for the development of novel functional surfaces that possess an increased resistance to bacterial contamination and infection. We propose a biophysical model of the interactions between bacterial cells and cicada wing surface structures, and show that mechanical properties, in particular cell rigidity, are key factors in determining bacterial resistance/sensitivity to the bactericidal nature of the wing surface. We confirmed this experimentally by decreasing the rigidity of surface-resistant strains through microwave irradiation of the cells, which renders them susceptible to the wing effects. Our findings demonstrate the potential benefits of incorporating cicada wing nanopatterns into the design of antibacterial nanomaterials.     

Mimicking a Superhydrophobic Insect Wing by Argon and Oxygen Ion Beam Treatment on Polytetrafluoroethylene Film

Biological tiny structures have been observed on many kinds of surfaces such as lotus leaves and insect wings,whichenhance the hydrophobicity of the natural surfaces and play a role of self-cleaning.We presented the fabrication technology of asuperhydrophobic surface using high energy ion beam.Artificial insect wings that mimic the morphology and the superhydrophobocityof cicada’s wings were successfully fabricated using argon and oxygen ion beam treatment on a polytetrafluoroethylene(PTFE)film.The wing structures were supported by carbon/epoxy fibers as artificial flexible veins that were bondedthrough an autoclave process.The morphology of the fabricated surface bears a strong resemblance to the wing surface of acicada,with contact angles greater than 160°,which could be sustained for more than two months.     

Relevance of crustacean carapace wettability for fouling

Carapace wettability and density of fouling organisms (bacteria, diatoms, protozoa, fungi, macro-organisms) were investigated for 45 crustacean species (Hoplocarida, Decapoda) from 15 families in the Gulf of Thailand. The results show that crustaceans can create and maintain characteristic carapace wettabilities. About 21 species (47%) possess highly wettable carapaces with contact angles below 20°. Contact angles between 20° and 40° were recorded for four species (2%), angles between 40° and 60° for eight species (4%) and from 60° to 70° for 11 (24%) species. One species, Alpheus euphrosyne (Alpheidae, Decapoda), exhibited an extremely low surface wettability (contact angle: 91°). Densities of colonisers and contact angles did not correlate. Very low wettability by water ( > 90°) may only contribute little to fouling reduction in A. euphrosyne which showed the most hydrophobic carapace surface and was colonised by the lowest numbers of bacteria among all species and no other colonisers at all. We conclude that surface wettability is of little relevance for antifouling defence in crustaceans.     

Morphometrics of the final instar exuviae of five cicada species occurring in urban areas of central Korea

Cicadas produce loud calling songs for mate attraction that can be a nuisance to city dwellers in Korea. Exuviae of final instars can be used to estimate population density. We investigated the morphological characteristics of final instar exuviae for five cicada species that are abundant in central Korea: Cryptotympana atrata, Hyalessa fuscata, Graptopsaltria nigrofuscata, Meimuna opalifera, and Meimuna mongolica. The characters analyzed were pro-mesonotum length, pronotum width, pronotum length, head width, abdominal circumference, body length, wing length, and femoral tooth angle. The results of a general linear model showed that species and sex were significant for morphological characters, and the result of post hoc analyses revealed that the mean values of most of the morphological characters measured were significantly different among the five cicada species. Three groups, Cryptotympana atrata, H. fuscata/G. nigrofuscata, and M. opalifera/M. mongolica, were distinctively identified based on most morphological characters. The distributions of femoral tooth angles did not overlap between H. fuscata and G. nigrofuscata, and the distributions of abdominal circumference did not overlap between M. opalifera and M. mongolica. Thus, the exuviae of all five cicada species could be easily distinguished based on morphological characters. We also provide a morphological key for the exuviae of all five cicada species in Korea.     

Ultrastructure of the corneal stroma: a comparative study.

Using a high intensity synchrotron x-ray source, we have recorded diffraction over a range of angles from the corneas of a wide variety of species. The results show that the interfibrillar Bragg spacing varies from 39 nm to 67 nm, the fibril diameter varies from 24 nm to 43 nm, but in the species studied intermolecular Bragg spacing is constant (1.58 +/- 0.03 nm). Using these data, a number of other structural parameters were calculated including the interfibrillar volume, V, and the surface-to-surface fibril separation, S. Large variations were found, particularly between aquatic and terrestrial animals. We found that the parameter which appears to be most constant throughout the species was the volume fraction, that is, the proportion of the tissue occupied by the hydrated fibrils. Ignoring the volume of the stroma occupied by cells, the tissue fibril volume fraction was (28 +/- 3)% for both aquatic and land animals. The observation of a constant volume fraction led us to propose a simple model in which collagen molecules and interfibrillar glycosaminoglycans occur in a fixed ratio in all the species--thus species with narrow fibrils have fewer interfibrillar glycosaminoglycans and the fibrils are thus more closely spaced, and vice versa. This model agrees with many of the experimental data on corneal composition and on the physical properties of the tissue reported in the literature.     

Ultrastructure of the capsule of Bacillus megaterium ATCC 19213.

The ultrastructure of the firmly adherent capsule produced by Bacillus megaterium cultured on fructose mineral salts medium was examined using thin sectioning, freeze-etching, and critical point drying by transmission and scanning electron microscopy. The capsule material was shown to be fibrillar, with most fibrils containing bulbous protrusions. Two types of fibres were resolved. These were termed primary and cross-linking fibres. Primary fibres originated at the cell wall and had a diameter of 34-50 nm. They also contained bulbous protrusions and enlarged areas where branching occurred. Cross-linking fibres connected the primary fibres. The cross-linking fibres were much smaller, usually 15 micro m in diameter, and contained few enlarged areas. The primary fibres originated at sites on the cell wall approximately equidistant and 0.26 micro m apart.     

The hypothalamo-hypophysial system of the lamprey,Lampetra fluviatilis L.

The proximal neurosecretory contact region (PNCR) of the lamprey, a homologue of the median eminence of tetrapods, was studied by light, fluorescence and electron microscopy. Paraldehyde fuchsin-positive neurosecretory fibers are seen mainly in the central part of the rostral subdivision of the PNCR. The Falck-Hillarp technique reveals a weak, mainly diffuse yellow-green fluorescence in the PNCR. The ultrastructure of the tanycyte layer of the PNCR is very similar to that in the neurohypophysis of the same species, although the funnel-shaped protrusions of the third ventricle in the rostral part of the PNCR are more frequent than in the neurophypophysis. Peptidergic A1 and A2 neurosecretory fibers are characterized by neurosecretory granules of 120-200 nm and 100-150 nm in diameter, respectively. Monoaminergic B type fibers contain granules 80-100 nm in diameter. Neurosecretory terminals and the vascular endfeet of tanycytes make contact with the basement membrane of the avascular connective tissue layer separating the PNCR from the hypophysial pars distalis. It is suggested that both peptide and monoamine neurohormones diffuse through the thick connective tissue septa into the underlying blood vessels which supply the pars distalis and thus affect the function of its glandular cells.     

A theoretical approach to the relationship between wettability and surface microstructures of epidermal cells and structured cuticles of flower petals

Background and Aims The epidermal surface of a flower petal is composed of convex cells covered with a structured cuticle, and the roughness of the surface is related to the wettability of the petal. If the surface remains wet for an excessive amount of time the attractiveness of the petal to floral visitors may be impaired, and adhesion of pathogens may be promoted. However, it remains unclear how the epidermal cells and structured cuticle contribute to surface wettability of a petal.Methods By considering the additive effects of the epidermal cells and structured cuticle on petal wettability, a thermodynamic model was developed to predict the wetting mode and contact angle of a water droplet at a minimum free energy. Quantitative relationships between petal wettability and the geometries of the epidermal cells and the structured cuticle were then estimated. Measurements of contact angles and anatomical traits of petals were made on seven herbaceous species commonly found in alpine habitats in eastern Nepal, and the measured wettability values were compared with those predicted by the model using the measured geometries of the epidermal cells and structured cuticles.Key Results The model indicated that surface wettability depends on the height and interval between cuticular steps, and on a height-to-width ratio for epidermal cells if a thick hydrophobic cuticle layer covers the surface. For a petal epidermis consisting of lenticular cells, a repellent surface results when the cuticular step height is greater than 0·85 µm and the height-to-width ratio of the epidermal cells is greater than 0·3. For an epidermis consisting of papillate cells, a height-to-width ratio of greater than 1·1 produces a repellent surface. In contrast, if the surface is covered with a thin cuticle layer, the petal is highly wettable (hydrophilic) irrespective of the roughness of the surface. These predictions were supported by the measurements of petal wettability made on flowers of alpine species.Conclusions The results indicate that surface roughness caused by epidermal cells and a structured cuticle produces a wide range of petal wettability, and that this can be successfully modelled using a thermodynamic approach.     

白蚁翅面微刻点的扫描电镜观察：堆砂白蚁属、楹白蚁属和原白蚁属

用扫描电镜观察了3种木白蚁(平阳堆砂白蚁Cryptotermes pingyangensis、叶额堆砂白蚁C.Havilandi和侧角楹白蚁Incisistermes laterangularis)和2种草白蚁(东方原白蚁Hodotermopsis orientalis和尤氏原白蚁H.Yui的翅面微刻点。微刻点类型有：乳突：基部宽5.0-20.6μm,长3.0-19.7μm,翅面中央密度可达2070-3375乳突mm²;瘤状突起：基部直径15.0-58.6μm,翅面中密度282-356突起/mm²;粉刺状突起：基部直径2.4-4.8μm。此外,还发现有长11一57μm的毛。同种白蚁的前、后翅和翅的背、腹面之间,微刻点类型没有明显的差异。最后初步讨论了白蚁翅面微刻点的分类学和生物学意义。     

Wettability and Contaminability of Insect Wings as a Function of Their Surface Sculptures

Abstract The wing surfaces of 97 insect species from virtually all relevant major groups were examined by high resolution scanning-electron-microscopy, in order to identify the relationships between the wing microstructures, their wettability with water and their behaviour under the influence of contamination. Isolated wings with contact angles between 31.6° and 155.5° were artificially contaminated with silicate dusts and subsequently fogged until drops of water (“dew”) formed and rolled off. The remaining particles were counted via a digital image analysis system. Remaining particle values between 0.41% and 103% were determined in comparison with unfogged controls. Some insects with very unwettable wings show a highly significant “self-cleaning” effect under the influence of rain or dew. Detailed analysis revealed that there is a correlation between the wettability and the “SM Index” (quotient of wing surface/(body mass)^0.67) with values ranging from 2.42 to 57.0. Furthermore, there is a correlation between the “self-cleaning” effect and the SM Index, meaning that taxa with a high SM Index, e.g. “large-winged” Ephemeroptera, Odonata, Planipennia, and many Lepidoptera, have very unwettable wings and show high particle removal due to dripping water drops. The “small-winged” insects, such as Diptera and Hymenoptera, and insects with elytra, such as Blattariae, Saltatoria, Heteroptera and Coleoptera, show completely opposite effects. This is clearly a result of the fact that species with a high SM Index are, in principle, more restricted in flight by contamination than species with a low SM Index which can also actively clean their own wings. The wings primarily serve a protection function in insects with elytra, so that the effects of contamination are probably of minor importance in these insects. Copyright © 1996 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.     

Hierarchical assembly and the onset of banding in fibrous long spacing collagen revealed by atomic force microscopy.

The mechanism of formation of fibrillar collagen with a banding periodicity much greater than the 67 nm of native collagen, i.e. the so-called fibrous long spacing (FLS) collagen, has been speculated upon, but has not been previously studied experimentally from a detailed structural perspective. In vitro, such fibrils, with banding periodicity of approximately 270 nm, may be produced by dialysis of an acidic solution of type I collagen and alpha(1)-acid glycoprotein against deionized water. FLS collagen assembly was investigated by visualization of assembly intermediates that were formed during the course of dialysis using atomic force microscopy. Below pH 4, thin, curly nonbanded fibrils were formed. When the dialysis solution reached approximately pH 4, thin, filamentous structures that showed protrusions spaced at approximately 270 nm were seen. As the pH increased, these protofibrils appeared to associate loosely into larger fibrils with clear approximately 270 nm banding which increased in diameter and compactness, such that by approximately pH 4.6, mature FLS collagen fibrils begin to be observed with increasing frequency. These results suggest that there are aspects of a stepwise process in the formation of FLS collagen, and that the banding pattern arises quite early and very specifically in this process. It is proposed that typical 4D-period staggered microfibril subunits assemble laterally with minimal stagger between adjacent fibrils. alpha(1)-Acid glycoprotein presumably promotes this otherwise abnormal lateral assembly over native-type self-assembly. Cocoon-like fibrils, which are hundreds of nanometers in diameter and 10-20 microm in length, were found to coexist with mature FLS fibrils.