Elastic modulus of tree frog adhesive toe pads

Barnes, W. Jon. P.; Goodwyn, P. J. Perez; Nokhbatolfoghahai, Mohsen; Gorb, Stanislav N.

doi:10.1007/s00359-011-0658-1

Cited by 81 publications

(107 citation statements)

References 52 publications

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“…With an estimated thickness h of approximately 1 mm and a Young's modulus E of 25 kPa for the adhesive toe pad (indentation experiments of Barnes et al [42]), the predicted force values (black dashed line in figure 6) give a reasonable fit for large peeling angles (greater than 458) but seriously underestimate the larger force values at small peeling angles by reaching a maximum at 8.9 Nm 21 .…”

Section: Pure Extension Componentmentioning

confidence: 93%

Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

Endlein

Samuel

et al. 2013

J. R. Soc. Interface.

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To live and clamber about in an arboreal habitat, tree frogs have evolved adhesive pads on their toes. In addition, they often have long and slender legs to facilitate not only long jumps, but also to bridge gaps between leaves when climbing. Both adhesive pads and long limbs are used in conjunction, as we will show in this study. Previous research has shown that tree frogs change from a crouched posture (where the limbs are close to the body) to a sprawled posture with extended limbs when clinging on to steeper inclines such as vertical or overhanging slopes. We investigated this change in posture in White's tree frogs (Litoria caerulea) by challenging the frogs to cling onto a tiltable platform. The platform consisted of an array of 24 three-dimensional force transducers, which allowed us to measure the ground reaction forces of the frogs during a tilt. Starting from a crouched resting position, the normal forces on the forelimbs changed sign and became increasingly negative with increasing slope angle of the platform. At about 1068 + 128, tilt of the platform the frogs reacted by extending one or two of their limbs outwards. At a steeper angle (1318 + 118), the frogs spread out all their limbs sideways, with the hindlimbs stretched out to their maximum reach. Although the extension was strongest in the lateral direction, limbs were significantly extended in the fore-aft direction as well. With the extension of the limbs, the lateral forces increased relative to the normal forces. The large contribution of the in-plane forces helped to keep the angle between the force vector and the platform small. The Kendall theory for the peeling of adhesive tape predicts that smaller peel angles lead to higher attachment forces. We compare our data with the predictions of the Kendall model and discuss possible implications of the sliding of the pads on the surface. The forces were indeed much larger for smaller angles and thus can be explained by peeling theory.

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Section: Pure Extension Componentmentioning

confidence: 93%

Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

Endlein

Samuel

et al. 2013

J. R. Soc. Interface.

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“…Their dense packing resembles the structure of many composite materials and would confer higher mechanical strength and flexibility to the epithelial cells. As frog toe pads have a low elastic modulus [23,41], such keratinization probably serves to increase the wear resistance of the outermost part of the toe pads. Whether the keratin tonofilaments have a particular role in adhesion, as they do in insects [26], remains to be investigated.…”

Section: Discussionmentioning

confidence: 99%

Morphological studies of the toe pads of the rock frog,Staurois parvus(family: Ranidae) and their relevance to the development of new biomimetically inspired reversible adhesives

et al. 2015

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The morphology of the toe epithelium of the rock frog, Staurois parvus (Family Ranidae), was investigated using a variety of microscopical techniques. The toe pad epithelium is stratified (four to five cell layers), the apical parts of the cells of the outermost layer being separated by fluid-filled channels. The surface of these cells is covered by a dense array of nanopillars, which also cover the surface of subarticular tubercles and unspecialized ventral epithelium of the toes, but not the dorsal epithelium. The apical portions of the outer two layers contain fibrils that originate from the nanopillars and are oriented approximately normal to the surface. This structure is similar to the pad structure of tree frogs of the families Hylidae and Rhacophoridae, indicating evolutionary convergence and a common evolutionary design for reversible attachment in climbing frogs. The main adaptation to the torrent habitat seems to be the straightness of the channels crossing the toe pad, which will assist in drainage of excess water. The presence of nanopillar arrays on all ventral surfaces of the toes resembles that on clingfish suckers and may be a specific adaptation for underwater adhesion and friction. The relevance of these findings to the development of new biomimetically inspired reversible adhesives is discussed.

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“…The typical organization of these proteins is essential both in withstanding mechanical stress and in adjusting to surface irregularities. Despite multiple morphological and histological studies [1,2,[4][5][6][7][8], the major structural proteins making up the complex amphibian toe pad remain largely unknown.…”

Section: Introductionmentioning

confidence: 99%

Recurrent functional divergence of early tetrapod keratins in amphibian toe pads and mammalian hair

et al. 2013

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Amphibians have invaded arboreal habitats multiple times independently during their evolution. Adaptation to these habitats was nearly always accompanied by the presence or appearance of toe pads, flattened enlargements on tips of fingers and toes that provide adhesive power in these environments. The strength and elasticity of the toe pad relies on polygonal arrayed cells ending in nanoscale projections, which are densely packed with cytoskeletal proteins. Here, we characterized and determined the evolutionary origin of these proteins in the toe pad of the tree frog Hyla cinerea. We created a subtracted cDNA library enriching genes that are expressed in the toe pad, but nowhere else in the toe. Our analyses revealed five alpha keratins as main structural proteins of the amphibian toe pad. Phylogenetic analyses show that these proteins belong to different keratin lineages that originated in an early tetrapod ancestor and in mammals evolved to become the major keratin types of hair. The ancestral keratins were probably already expressed in areas that required skin reinforcement in early tetrapods, and subsequently diverged to support fundamentally different adaptive structures in amphibians and mammals.

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Elastic modulus of tree frog adhesive toe pads

Cited by 81 publications

References 52 publications

Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

Sticking like sticky tape: tree frogs use friction forces to enhance attachment on overhanging surfaces

Morphological studies of the toe pads of the rock frog,Staurois parvus(family: Ranidae) and their relevance to the development of new biomimetically inspired reversible adhesives

Recurrent functional divergence of early tetrapod keratins in amphibian toe pads and mammalian hair

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