The long period of reciprocal antagonistic coevolution between some insect and plant species has led to the development of plant surface attributes that reduce insect attachment. These features serve ...as a defence against herbivores, sap-sucking insects and nectar robbers, contribute to a temporary capture of insect pollinators, and prevent the escape of insects from traps of carnivorous plants. This review summarises the literature on attachment-mediated insect–plant interactions. A short introduction to attachment systems of insects is presented and the effect of three-dimensional epicuticular waxes on insect attachment is illustrated by many examples. Special attention is given to the mechanisms of the anti-attachment properties of plant wax structures (the roughness hypothesis, the contamination hypothesis, the fluid-adsorption hypothesis, and the wax-dissolving hypothesis) and their ecological implications.
Adhesion is a fundamental phenomenon with great importance in technology, in our everyday life, and in nature. In this article, we review physical interactions that resist the separation of two ...solids in contact. By using examples of biological attachment systems, we summarize and categorize various principles that contribute to the so-called gecko effect. Emphasis is placed on the contact geometry and in particular on the mushroom-shaped geometry, which is observed in long-term biological adhesive systems. Furthermore, we report on artificial model systems with this bio-inspired geometry and demonstrate that surface microstructures with this geometry are promising candidates for technical applications, in which repeatable, reversible, and residue-free adhesion under different environmental conditions-such as air, fluid, and vacuum-is required. Various applications in robotic systems and in industrial pick-and-place processes are discussed.
For an insect to be able to efficiently attach to surfaces, the adhesive pads on the distal parts of its legs must establish large contact areas. In case of hairy adhesive pads this requires ...flexibility of the contact-forming bristles, called adhesive tarsal setae. However, too flexible setae would have a low mechanical stability resulting in a decreased attachment ability of the pads. Here we show that the adhesive tarsal setae of the ladybird beetle Coccinella septempunctata feature pronounced gradients in the material composition and properties along their length. The Young's modulus ranges from 1.2 MPa at the tips, where we found the incorporation of high proportions of the elastic protein resilin, to 6.8 GPa at the bases of the setae. These gradients likely represent an evolutionary optimization, which increases the performance of the adhesive system by enabling effective adaptation to rough surfaces while simultaneously preventing lateral collapse of the setae.
One molluscan autapomorphy is the radula, the organ used for feeding. Here, for the first time, the performance and failure of taenioglossan radular teeth were tested in a biomechanical experiment ...which in turn allowed building hypotheses about tooth functionalities. Shear load was applied to tooth cusps with a force transducer until structural failure occurred, the broken area was measured, and finally breaking stress was calculated. These experiments were carried out under dry and wet conditions. Our results show that certain tooth types can resist higher stresses and are rather specialised to loosen food items from a surface, whereas other teeth can only gather food particles. The experiments additionally illustrate the high influence of the water content on the resulting breaking stress. When wet teeth were tested, their ductility and ability to avoid being fractured by an obstacle increased. Their flexibility also allowed them support from teeth of adjacent tooth rows, which made the whole system less prone to failure. Our results were compared with the previous data on the mechanical properties and feeding simulations. This study provides a keystone for further comparative studies aiming at connecting diversity of radulae with their possible adaptations to the ingesta.
Despite extensive efforts to mimic the fascinating adhesion capability of geckos, the development of reversible adhesives underwater has long been lagging. The appearance of mussels‐inspired dopamine ...chemistry has provided the feasibility to fabricate underwater adhesives; however, for such a system, imitating the reversible and fast dynamic attachment/detachment mechanism of gecko feet still remains unsolved. Here, by synthesizing a thermoresponsive copolymer of poly(dopamine methacrylamide‐co‐methoxyethyl‐acrylate‐co‐N‐isopropyl acrylamide) and then decorating it onto mushroom‐shaped poly(dimethylsiloxane) pillar arrays, a novel underwater thermoresponsive gecko‐like adhesive (TRGA) can be fabricated, yielding high adhesion during the attachment state above the lower critical solution temperature (LCST) of the copolymer, yet low adhesion during the detachment state below the LCST of the copolymer. By integrating the Fe3O4 nanoparticles into the TRGA, TRGAs responsive to near‐infrared laser radiation can be engineered, which can be successfully used for rapid and reversible remote control over adhesion so as to capture and release heavy objects underwater because of the contrast force change of both the normal adhesion force and the lateral friction force. It is also demonstrated that the material can be assembled on the tracks of an underwater mobile device to realize controllable movement. This opens up the door for developing intelligent underwater gecko‐like locomotion with dynamic attachment/detachment ability.
A kind of intelligent underwater thermoresponsive gecko adhesive (TRGA) with switchable adhesion feature is prepared in response to temperature change triggered by external near‐infrared light. The TRGA can exhibit low adhesion/friction force against contact surfaces at low temperature, but high adhesion/friction force at high temperature underwater along with excellent reversibility, which enables successful manufacture of mobile robots underwater/or in wet conditions.
Biological tissues may exhibit graded heterogeneities in structure and mechanical properties that are crucial to their function. One biological structure that shows variation in both structure and ...function is the molluscan radula: the organ comprises a chitinous membrane with embedded teeth and serves to process and gather food. The tooth morphologies had been well studied in the last decades, but the mechanical properties of the teeth are not known for the vast majority of molluscs. This knowledge gap restricts our understanding of how the radula is able to act effectively on a target surface whilst simultaneously resisting structural failure. Here we employed nanoindentation technique to measure mechanical properties (hardness and Young's modulus) on distinct localities of individual radular teeth from 24 species of African paludomid gastropods. These species have distinct ecological niches as they forage on algae on different feeding substrates. A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. The presence or absence of large-scale gradients in these taenioglossan teeth could directly be linked with their specific function and in general with the species ecology, whereas the radular tooth morphologies do not always and fully reflect ecology.
African Lake Tanganyika is well known for harbouring endemic and morphologically distinct genera. Its paludomid gastropods form a flock of high interest because of its diversity. As they show distinct radular tooth morphologies hypotheses about potential trophic specializations had always been at hand. Here we evaluated the mechanical properties Young’s modulus and hardness of 9027 individual teeth from 24 species along the tooth by nanoindentation and related them with the gastropods’ specific feeding substrate. We find that hard substrate feeders have teeth that are hard at the tips but much less stiff at the base and thus heterogeneous with respect to material properties, whereas soft substrate feeders have teeth that are flexible and homogenous with respect to material properties.
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Many species of animals and plants are supplied with diverse attachment devices, in which morphology depends on the species biology and the particular function in which the attachment device is ...involved. Many functional solutions have evolved independently in different lineages of animals and plants. Since the diversity of such biological structures is huge, there is a need for their classification. This paper, based on the original and literature data, proposes ordering of biological attachment systems according to several principles: (i) fundamental physical mechanism, according to which the system operates, (ii) biological function of the attachment device, and (iii) duration of the contact. Finally, we show a biomimetic potential of studies on biological attachment devices.
The molluscan radula, a thin membrane with embedded rows of teeth, is the structure for food processing and gathering. For proper functioning, radular failures must be either avoided or reduced when ...interacting with the preferred food, as this might be of high significance for the individual fitness. Thus, the analysis of structural failure in radular teeth could be included in studies on trophic specializations. Here, we tested the failure of non-mineralized, chitinous radular teeth from taxa, belonging to an African paludomid species flock from Lake Tanganyika and surrounding river systems. These species are of high interest for evolutionary biologists since they represent a potential result of an adaptive radiation including trophic specialisations to distinct substrates, the food is attached to. In a biomechanical experiment a shear load was applied to tooth cusps with a force transducer connected to a motorized stage until structural failure occurred. Subsequently broken areas were measured and breaking stress was calculated. As the experiments were carried out under dry and wet conditions, the high influence of the water content on the forces, teeth were capable to resist, could be documented. Wet teeth were able to resist higher forces, because of their increased flexibility and the flexibility of the embedding membrane, which enabled them either to slip away or to gain support from adjacent teeth. This mechanism can be understood as collective effect reducing structural failure without the mineralisation with wear-minimizing elements, as described for Polyplacophora and Patellogastropoda. Since the documented mechanical behaviour of radular teeth and the maximal forces, teeth resist, can directly be related to the gastropod ecological niche, both are here identified as an adaptation to preferred feeding substrates.
The radula, a chitinous membrane with teeth, is the molluscan feeding structure. Here we add onto existing knowledge about the relationship between tooth's mechanical properties and species’ ecology by determining the tooth failure resistance. Six paludomid species (Gastropoda) of a prominent species flock from Lake Tanganyika, foraging on distinct feeding substrates, were tested. With a force transducer wet and dry teeth were broken, revealing the high influence of water content on mechanical behaviour and force resistance of teeth. Higher forces were needed to break wet radulae due to an increased flexibility of teeth and membrane, which resulted in an interlocking or twisting of teeth. Mechanical behaviour and force resistance were both identified as trophic adaptations to feeding substrate.
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Plant seeds and fruits, like those of Ocimum basilicum, develop a mucilaginous envelope rich in pectins and cellulosic fibers upon hydration. This envelope promotes adhesion for attachment to soils ...and other substrates for dispersal and protection of the seed for a safe germination. Initially at hydration, the mucilage envelope demonstrates low adhesion and friction, but shows increasing adhesive and frictional properties during dehydration. However, the mechanisms underlying the cellulose fiber arrangement and the mechanical properties, especially the elasticity modulus of the mucilage envelope at different hydration conditions are not fully known. In this study, which is based on scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and light microscopy, the structure of the seed coat and arrangement of the cellulose fibers of basil seeds were characterized. Moreover, we performed pull-off force measurements to estimate adhesive properties and JKR-tests to estimate E-modulus of the mucilage at different hydration levels. Microscopy results demonstrate that cellulose fibers are split at their free ends into smaller fibrils, which might enhance the adhesive properties of the mucilage. Adhesive forces in contact increased during dehydration and reached maximum of 33 mN shortly before complete dehydration. The E-modulus of the mucilage changed from 1.4 KPa in water to up to 2.1 MPa in the mucilage at the maximum of its adhesion performance. Obtained results showed hydrogel-like mechanical properties during dehydration and cellulose fiber structures similar to the nanofibrous systems in other organisms with strong adhesive properties.
This paper reveals the hierarchical cellulose fiber structure in Ocimum basilicum's mucilaginous seed coat, suggesting increased fiber splitting towards the end, potentially enhancing adhesion contact areas. Mechanical tests explore elasticity modulus and adhesion force during various hydration stages, crucial as these properties evolve with mucilage desiccation. A rare focus on mucilaginous seed coat mechanical properties, particularly cellulose-reinforced fibers, provides insight into the hydrogel-like mucilage of plant seeds. Adhesion forces peak just before complete desiccation and then decline rapidly. As mucilage water content decreases, the E-modulus rises, displaying hydrogel-like properties during early dehydration stages with higher water content. This study might bring the focus to plant seeds as inspiration for biodegradable glues and applications for hydrogel research.
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Asteraceae, one of the largest flowering plant families, are adapted to a vast range of ecological niches. Their adaptability is partially based on their strong ability to reproduce. The initial, yet ...challenging, step for the reproduction of animal-pollinated plants is to transport pollen to flower-visiting pollinators. We adopted Hypochaeris radicata as a model species to investigate the functional morphology of the typical floral feature of Asteraceae, a pollen-bearing style. Using quantitative experiments and numerical simulations, here we show that the pollen-bearing style can serve as a ballistic lever for catapulting pollen grains to pollinators. This can potentially be a pollen dispersal strategy to propel pollen to safe sites on pollinators' bodies, which are beyond the physical reach of the styles. Our results suggest that the specific morphology of the floret and the pollen adhesion avoid pollen waste by catapulting pollen within a specific range equal to the size of a flowerhead. The insights into the functional floral oscillation may shed light on the superficially unremarkable, but ubiquitous functional floral design of Asteraceae.
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