337 research outputs found
Mechanics of plant fruit hooks
No full textHook-like surface structures, observed in some plant species, play an important role in the process of plant growth and seed dispersal. In this study, we developed an elastic model and further used it to investigate the mechanical behaviour of fruit hooks in four plant species, previously measured in an experimental study. Based on Euler–Bernoulli beam theory, the force–displacement relationship is derived, and its Young's modulus is obtained. The result agrees well with the experimental data. The model aids in understanding the mechanics of hooks, and could be used in the development of new bioinspired Velcro-like materials
Kaolin nano-powder effect on insect attachment ability
No full textThe present study investigates under controlled conditions the effect of kaolin particle film on reduction of insect attachment ability. Two economically important polyphagous insect pests characterized by different attachment devices were tested, the Southern green stink bug Nezara viridula (Heteroptera: Pentatomidae) and the Mediterranean fruit fly Ceratitis capitata (Diptera: Tephritidae). We performed traction force experiments with females pulling on treated (covered with kaolin par- ticle film) and untreated (control) natural (leaf surfaces with different morphological traits) and artificial (hydrophilic and hydrophobic glass) surfaces. The data demonstrated that insect adhesion is heavily affected by kaolin particle film in both tested species. The degree of reduction of insect adhesion to the treated substrates compared with the untreated ones differed according to the kind of treated substrate owing to its initial wettability and morphology (presence of trichomes). To unravel the insect adhesion reduction mechanism of kaolin particle film, we evaluated the safety factor for females before and after walking on treated surfaces and analyzed under cryo-SEM the tarsal attachment devices of N. viridula and C. capitata after walking on treated surfaces. We observed contamination by the kaolin nanoflakes in both the smooth pads of the bug and the hairy pads of the fly. The present study can help to better understand the mechanism of action of kaolin particle film and can contribute to develop future physical control barriers against pest insects, particularly relevant owing to the need to reduce the negative impacts of pesticides on environment and human healt
Ruolo della variazione di larghezza e di spessore nelle spatole delle lucertole e degli insetti
No full textMolti dispositivi biologici di adesione degli insetti, dei ragni e dei gechi consistono di matrici di peli (setae) che terminano con elementi di contatto di diverse forme. Tuttavia, la forma più osservata è una spatola appiattita. Nonostante nei diversi animali le spatole esistano in una notevole varietà di dimensioni, la maggior parte di esse non sono uniformi ma posseggono un gradiente sia in spessore che in larghezza. In questo lavoro investighiamo perché le spatole dei gechi diventano gradualmente più sottili e più larghe avvicinandosi alla loro estremità. Il motivo di questa particolare geometria è studiato utilizzando un approccio numerico basato sul metodo degli elementi finiti. La modellazione numerica del peeling della singola spatola richiede l’introduzione delle forze di van der Waals tra spatole e substrato. I risultati numerici suggeriscono che la variazione di spessore e di larghezza delle spatole sono entrambe utili per migliorare la capacità dell’animale di camminare
Mechanical interaction of the egg parasitoid Anastatus bifasciatus (Hymenoptera: Eupelmidae) with artificial substrates and its host egg
No full textEgg parasitoids play an important role in biological control of pest species attacking and killing their hosts at an early stage of their development. During the antagonistic coevolution with their hosts, egg parasitoids have developed a great ability to locate their host using chemical cues. A considerable amount of literature is available on this topic, while nothing is known about a possible adaptation of egg parasitoids to topography and mechanical properties of egg surface features and its shape when attaching to the host egg for oviposition. In the present investigation, the attachment ability of adults of both sexes of the egg parasitoid Anastatus bifasciatus (Hymenoptera: Eupelmidae) to artificial (polishing paper, flat glass, glass beads as dummies of the host egg) and natural surfaces (eggs of Halyomorpha halys and Nezara viridula, both Heteroptera: Pentatomidae), with different roughness and wettability, was measured using centrifugal force tester and traction force experiments. The parasitoid attachment devices and the egg surfaces were examined under cryo scanning electron microscope, wettability and roughness of natural and artificial substrates were characterised. We detected differences in the attachment devices and attachment ability of the two sexes. The collected data revealed a special ability of the female to attach to the eggs of the host species, thus suggesting an adaptation of the A. bifasciatus female to the surface features of the eggs during oviposition
Attachment devices and the tarsal gland of the bug Coreus marginatus (Hemiptera: Coreidae)
No full textThe present ultrastructural investigation using scanning and transmission electron microscopy as well as light and fluorescence microscopy describes in detail the attachment devices and tarsal gland of the bug Coreus marginatus (L.) (Hemiptera: Coreidae). In particular, the fine structure of pulvilli reveals a ventral surface rich with pore channels, consistent with fluid emission, and a folded dorsal surface, which could be useful to enhance the pulvillus contact area during attachment to the substrate. The detailed description of the tarsal gland cells, whose structure is coherent with an active secretory function, allows us to consider the tarsal gland as the plausible candidate for the adhesive fluid production. Scolopidia strictly adhering to the gland cells are also described. On the basis of the fine structure of the tarsal gland, we hypothesise a fluid emission mechanism based on changes of the hydraulic pressure inside the gland, due to the unguitractor tendon movements. This mechanism could provide the fluid release based on compression of the pad and capillary suction, as demonstrated in other insects. The data here reported can contribute to understanding of insect adhesive fluid production, emission and control of its transport
Origin of the superior adhesive performance of mushroom-shaped microstructured surfaces
No full textThe superlative adhesive properties of some biological attachment systems, such as those of geckos, spiders, and insects, have inspired researchers from different fields (e.g. biology, physics and engineering) to conceive and design man-made microstructured surfaces that might mimic their performance. Among the several proposed designs, very recently mushroom-shaped adhesive microstructures have drawn the interest of scientists and engineers, because experiments have proved their superiority compared to other micro- and nano-structures. In this article, we explain theoretically the physical mechanism behind the enhanced adhesion of such microstructures, and provide for the first time a useful tool to predict adhesive performance depending on the geometry, mechanical properties of the material, and energy of adhesion. Our theoretical predictions are strongly supported by the available experimental data. The present study can streamline the optimisation of adhesive microstructures for industrial applications
Direct observation of microcavitation in underwater adhesion of mushroom-shaped adhesive microstructure
No full textIn this work we report on experiments aimed at testing the cavitation hypothesis [Varenberg, M.; Gorb, S. J. R. Soc., Interface 2008, 5, 383–385] proposed to explain the strong underwater adhesion of mushroom-shaped adhesive microstructures (MSAMSs). For this purpose, we measured the pull-off forces of individual MSAMSs by detaching them from a glass substrate under different wetting conditions and simultaneously video recording the detachment behavior at very high temporal resolution (54,000–100,000 fps). Although microcavitation was observed during the detachment of individual MSAMSs, which was a consequence of water inclusions present at the glass–MSAMS contact interface subjected to negative pressure (tension), the pull-off forces were consistently lower, around 50%, of those measured under ambient conditions. This result supports the assumption that the recently observed strong underwater adhesion of MSAMS is due to an air layer between individual MSAMSs [Kizilkan, E.; Heepe, L.; Gorb, S. N. Underwater adhesion of mushroom-shaped adhesive microstructure: An air-entrapment effect. In Biological and biomimetic adhesives: Challenges and opportunities; Santos, R.; Aldred, N.; Gorb, S. N.; Flammang, P., Eds.; The Royal Society of Chemistry: Cambridge, U.K., 2013; pp 65–71] rather than by cavitation. These results obtained due to the high-speed visualisation of the contact behavior at nanoscale-confined interfaces allow for a microscopic understanding of the underwater adhesion of MSAMSs and may aid in further development of artificial adhesive microstructures for applications in predominantly liquid environments
Adhesion Tilt-Tolerancy in Bio-Inspired Mushroom-Shaped Adhesive Microstructure
No full textWe studied experimentally and theoretically the effect of different tilt angles on the adhesion of mushroom-shaped adhesive microstructures. The marginal measured influence of tilting on pull-off forces is quantitatively well confirmed by numerical and theoretical calculations and was shown to be a direct consequence of an optimized stress distribution. In addition, the presence of a joint-like narrowing under the contact elements, as found in some biological attachment systems, was shown to further contribute to the tilt-tolerance. The results obtained allow us to explain the advantage of the widely observed mushroom-shaped contact geometry in nature for long-term and permanent adhesion
Dermaptera
No full text9 Dermaptera <p>The second tarsomere of the three­segmented tarsus is distinctly shorter than the others in representatives of Dermaptera excluding Hemimerus (Gunther and Herter 1974; Figs 3d, 7D,E). The two proximal tarsomeres usually bear a dense brush of hairs on the ventral side (Gunther and Herter 1974). An arolium is found in hemimerines (Gunther and Herter 1974; Haas and Gorb, unpublished data).</p>Published as part of <i>R. G. Beutel & S. N. Gorb, 2001, Ultrastructure of attachment specializations of hexapods (Arthropoda): evolutionary patterns inferred from a revised ordinal phylogeny, pp. 177-207 in J. Zool. Syst. Evol. Research 39</i> on page 180, DOI: 10.1046/j.1439-0469.2001.00155.x, <a href="http://zenodo.org/record/2360323">http://zenodo.org/record/2360323</a>
THE ALLURE OF NATURAL AND ARTIFICIAL FOOD COLORS: THE POINT OF VIEW OF ANIMALS AND PLANTS
No full textFood colors are classified as natural if they are extracted from vegetal, microbial, animal or mineral sources and as artificial if they are produced in a laboratory. They are added to food and drink but also to cosmetics and pharmaceuticals to make the products more attractive. The use of these additives, especially artificial ones, has risen more than 5-fold in the last 60 years, with a consequent increase in the waste waters resulting from industrial and urban effluents. Concern for human health and the aquatic environment is consequently increasing but the toxicity of food colorings on flora and fauna remains poorly studied. In this framework, we tested the effects of two commercially available food colors, the natural cochineal red (E120) and the artificial Ponceau red (E124), on three model organisms, Cucumis sativus, Artemia salina and Danio rerio, that occupy diverse positions in the trophic pyramid. The organisms were exposed to the same concentration suggested for preparing food (650 mg per 500 mL milk or cream); the health of the organisms and the alterations induced were investigated. The data collected indicate that both colorings are toxic and that E124 causes damage to all three model organisms while E120 is apparently safer for Danio but induces alterations in Cucumis and Artemia. The overall results clearly demonstrate that our habit of artificially coloring the world around us is very unsafe for the aquatic flora and fauna and that natural is not necessarily better than artificial
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