When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs

Crawford, Niall Alexander; Endlein, Thomas; Pham, Jonathan T.; Riehle, Mathis O.; Barnes, W. Jon. P.

doi:10.3762/bjnano.7.201

Cited by 28 publications

(55 citation statements)

References 49 publications

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“…Only for H. cinerea, tenacities are significantly higher on the 0.1 µm and the 15 µm substrate compared to the smooth one. These results are only partially in line with the findings of Crawford et al [34], who described for single pads of L. caerulea significantly higher tenacities for R = 0.3-16 µm, if compared to a smooth substrate. Presumably, this disagreement between rotation platform experiments and single pad studies arises from differences in pad loading.…”

Section: Friction Performancesupporting

confidence: 81%

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Estimating the maximum attachment performance of tree frogs on rough substrates

Langowski

Rummenie²,

Pieters³

et al. 2019

Bioinspir. Biomim.

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Tree frogs can attach to smooth and rough substrates using their adhesive toe pads. We present the results of an experimental investigation of tree frog attachment to rough substrates, and of the role of mechanical interlocking between superficial toe pad structures and substrate asperities in the tree frog species Litoria caerulea and Hyla cinerea. Using a rotation platform setup, we quantified the adhesive and frictional attachment performance of whole frogs clinging to smooth, micro-, and macrorough substrates. The transparent substrates enabled quantification of the instantaneous contact area during detachment by using frustrated total internal reflection. A linear mixed-effects model shows that the adhesive performance of the pads does not differ significantly with roughness (for nominal roughness levels of 0-15 µm) in both species. This indicates that mechanical interlocking does not contribute to the attachment of whole animals. Our results show that the adhesion performance of tree frogs is higher than reported previously, emphasising the biomimetic potential of tree frog attachment. Overall, our findings contribute to a better understanding of the complex interplay of attachment mechanisms in the toe pads of tree frogs, which may promote future designs of tree-frog-inspired adhesives.

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Section: Friction Performancesupporting

confidence: 81%

“…≈ 300 nm for the nanopillars [21] and ≈ 10 µm for the epidermal cells [20]). The attachment forces generated by the other proposed attachment mechanisms might also be critically attenuated with increasing substrate roughness, for example by reducing the effective contact area [49] or by meniscus cavitation [34,50].…”

Section: Introductionmentioning

confidence: 99%

Estimating the maximum attachment performance of tree frogs on rough substrates

Langowski

Rummenie²,

Pieters³

et al. 2019

Bioinspir. Biomim.

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show abstract

“…This is well above the maximum load of 1.27 N measured for single digital pads of Trachycephalus resinifictrix (Bijma et al 2016). Considering peak shear stresses of up to 70 kPa (Rhacophorus dennysi; Endlein et al 2017) and 140 kPa (Litoria caerulea; Crawford et al 2016) withstood by the epidermal surface, and the high tensile strength of the collagen layer, we argue that the digital pads are adapted primarily towards the generation and transmission of frictional rather than adhesive forces. This agrees with the functional demands on the pad arising from the locomotion and habitat of tree frogs.…”

Section: Transmission Of Shear Loadsmentioning

confidence: 51%

“…) and 140 kPa ( Litoria caerulea ; Crawford et al. ) withstood by the epidermal surface, and the high tensile strength of the collagen layer, we argue that the digital pads are adapted primarily towards the generation and transmission of frictional rather than adhesive forces. This agrees with the functional demands on the pad arising from the locomotion and habitat of tree frogs.…”

Section: Discussionmentioning

confidence: 71%

Force‐transmitting structures in the digital pads of the tree frog Hyla cinerea: a functional interpretation

et al. 2018

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The morphology of the digital pads of tree frogs is adapted towards attachment, allowing these animals to attach to various substrates and to explore their arboreal habitat. Previous descriptions and functional interpretations of the pad morphology mostly focussed on the surface of the ventral epidermis, and little is known about the internal pad morphology and its functional relevance in attachment. In this study, we combine histology and synchrotron micro‐computer‐tomography to obtain a comprehensive 3‐D morphological characterisation of the digital pads (in particular of the internal structures involved in the transmission of attachment forces from the ventral pad surface towards the phalanges) of the tree frog Hyla cinerea. A collagenous septum runs from the distal tip of the distal phalanx to the ventral cutis and compartmentalises the subcutaneous pad volume into a distal lymph space and a proximal space, which contains mucus glands opening via long ducts to the ventral pad surface. A collagen layer connects the ventral basement membrane via interphalangeal ligaments with the middle phalanx. The collagen fibres forming this layer curve around the transverse pad‐axis and form laterally separated ridges below the gland space. The topological optimisation of a shear‐loaded pad model using finite element analysis (FEA) shows that the curved collagen fibres are oriented along the trajectories of the maximum principal stresses, and the optimisation also results in ridge‐formation, suggesting that the collagen layer is adapted towards a high stiffness during shear loading. We also show that the collagen layer is strong, with an estimated tensile strength of 2.0–6.5 N. Together with longitudinally skewed tonofibrils in the superficial epidermis, these features support our hypothesis that the digital pads of tree frogs are primarily adapted towards the generation and transmission of friction rather than adhesion forces. Moreover, we generate (based on a simplified FEA model and predictions from analytical models) the hypothesis that dorsodistal pulling on the collagen septum facilitates proximal peeling of the pad and that the septum is an adaptation towards detachment rather than attachment. Lastly, by using immunohistochemistry, we (re‐)discovered bundles of smooth muscle fibres in the digital pads of tree frogs. We hypothesise that these fibres allow the control of (i) contact stresses at the pad–substrate interface and peeling, (ii) mucus secretion, (iii) shock‐absorbing properties of the pad, and (iv) the macroscopic contact geometry of the ventral pad surface. Further work is needed to conclude on the role of the muscular structures in tree frog attachment. Overall, our study contributes to the functional understanding of tree frog attachment, hence offering novel perspectives on the ecology, phylogeny and evolution of anurans, as well as the design of tree‐frog‐inspired adhesives for technological applications.

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“…[12][13][14][15][16][17] Natural adhesives have been the subject of several hundred years of research, [18,19] and the adhesion techniques of mussels, barnacles, and tree frogs have garnered considerable attention, inspiring an array of synthetic mimics. [20][21][22] Adhesives utilized by insects, however, have gone largely understudied when considering their diversity and abundance. [23] These insect adhesive systems exist as two overlapping categories: physical adhesive structures that mechanically interlock or generate attractive force through van der Waals' interactions, and chemical adhesive secretions that act via molecular bonding, capillary forces, and viscous forces.…”

Section: Adhesionmentioning

confidence: 99%

It's Not a Bug, It's a Feature: Functional Materials in Insects

2018

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Over the course of their wildly successful proliferation across the earth, the insects as a taxon have evolved enviable adaptations to their diverse habitats, which include adhesives, locomotor systems, hydrophobic surfaces, and sensors and actuators that transduce mechanical, acoustic, optical, thermal, and chemical signals. Insect‐inspired designs currently appear in a range of contexts, including antireflective coatings, optical displays, and computing algorithms. However, as over one million distinct and highly specialized species of insects have colonized nearly all habitable regions on the planet, they still provide a largely untapped pool of unique problem‐solving strategies. With the intent of providing materials scientists and engineers with a muse for the next generation of bioinspired materials, here, a selection of some of the most spectacular adaptations that insects have evolved is assembled and organized by function. The insects presented display dazzling optical properties as a result of natural photonic crystals, precise hierarchical patterns that span length scales from nanometers to millimeters, and formidable defense mechanisms that deploy an arsenal of chemical weaponry. Successful mimicry of these adaptations may facilitate technological solutions to as wide a range of problems as they solve in the insects that originated them.

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When the going gets rough – studying the effect of surface roughness on the adhesive abilities of tree frogs

Cited by 28 publications

References 49 publications

Estimating the maximum attachment performance of tree frogs on rough substrates

Estimating the maximum attachment performance of tree frogs on rough substrates

Force‐transmitting structures in the digital pads of the tree frog Hyla cinerea: a functional interpretation

It's Not a Bug, It's a Feature: Functional Materials in Insects

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