scholarly journals Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

2016 ◽  
Vol 13 (122) ◽  
pp. 20160373 ◽  
Author(s):  
David Labonte ◽  
Walter Federle
Keyword(s):  
Fluid Layer ◽  
Stick Insect ◽  
Linear Increase ◽  
Shear Forces ◽  
Conflicting Demands ◽  
Adhesive Pads ◽  
Direction Dependence ◽  
Peel Force ◽  
Induced Changes ◽  
Adhesive Forces

Many arthropods and small vertebrates use adhesive pads for climbing. These biological adhesives have to meet conflicting demands: attachment must be strong and reliable, yet detachment should be fast and effortless. Climbing animals can rapidly and reversibly control their pads' adhesive strength by shear forces, but the mechanisms underlying this coupling have remained unclear. Here, we show that adhesive forces of stick insect pads closely followed the predictions from tape peeling models when shear forces were small, but strongly exceeded them when shear forces were large, resulting in an approximately linear increase of adhesion with friction. Adhesion sharply increased at peel angles less than ca 30°, allowing a rapid switch between attachment and detachment. The departure from classic peeling theory coincided with the appearance of pad sliding, which dramatically increased the peel force via a combination of two mechanisms. First, partial sliding pre-stretched the pads, so that they were effectively stiffer upon detachment and peeled increasingly like inextensible tape. Second, pad sliding reduces the thickness of the fluid layer in the contact zone, thereby increasing the stress levels required for peeling. In combination, these effects can explain the coupling between adhesion and friction that is fundamental to adhesion control across all climbing animals. Our results highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of controllable bio-inspired adhesives.

scholarly journals Biomechanics of shear-sensitive adhesion in climbing animals: peeling, pre-tension and sliding-induced changes in interface strength

2015 ◽  
Author(s):  
David Labonte ◽  
Walter Federle
Keyword(s):  
Linear Increase ◽  
Shear Forces ◽  
Rapid Control ◽  
Stick Insects ◽  
Direction Dependence ◽  
Peel Force ◽  
Rapid Switching ◽  
Induced Changes ◽  
Interfacial Mobility ◽  
Adhesive Forces

Rapid control of adhesive forces is one of the key benchmarks where footpads of climbing animals outperform conventional adhesives, promising novel bio-inspired attachment systems. All climbing animals use shear forces to switch rapidly between firm attachment and easy detachment, but the detailed mechanisms underlying `shear-sensitive adhesion' have remained unclear. Here, we show that attachment forces of stick insects follow classic peeling theory when shear forces are small, but strongly exceed predictions as soon as their pads start to slide due to high shear forces. Pad sliding dramatically increases the critical peel force via a combination of two distinct mechanisms. First, partial sliding will pre-stretch the pads, so that they are effectively stiffer upon detachment and peel increasingly like inextensible tape. We demonstrate how this effect can be directly related to peeling theories which account for frictional dissipation. Second, pad sliding reduces the thickness of the secretion layer in the contact zone, thereby decreasing the interfacial mobility, and increasing the stress levels required for peeling. The approximately linear increase of adhesion with friction results in a sharp increase of adhesion at peel angles less than ca. 30°, allowing rapid switching between attachment and detachment during locomotion. Our results may apply to diverse climbing animals independent of pad morphology and adhesive mechanism, and highlight that control of adhesion is not solely achieved by direction-dependence and morphological anisotropy, suggesting promising new routes for the development of bio-inspired adhesives.

GDP binding to rat brown fat mitochondria: effects of thyroxine at different ambient temperatures

1981 ◽  
Vol 241 (3) ◽  
pp. C134-C139 ◽  
Author(s):  
U. Sundin
Keyword(s):  
Linear Increase ◽  
Reciprocal Relationship ◽  
Brown Fat ◽  
Hormone Activity ◽  
Ambient Temperatures ◽  
Heating Capacity ◽  
Brown Adipose ◽  
Induced Changes ◽  
Brown Fat Mitochondria

Reports on a reciprocal relationship between sympathetic-nerve and experimentally induced changes in thyroid-hormone activity called into question the proposed role of thyroxine in the changes seen in the brown fat after cold adaptation. Rats reared at +30, +22, and +5 degrees C received daily injections of thyroxine (1 mg/kg). After 3 wk of treatment, the thermogenic state of the tissue was assessed by measuring the capacity of the brown fat mitochondria to bind guanosine 5'-diphosphate (GDP). GDP-inhibited mitochondrial swelling, brown adipose tissue (BAT) wet weights, and mitochondrial yields were also measured. The control animals showed a linear increase in GDP binding between +30 and +5 degrees C. Thyroxine was found to lower the GDP binding markedly at +5 degrees C, less so at +22 degrees C, while no effect was evident at +30 degrees C. The values at +22 and +30 degrees C were identical. The other parameters studied all confirmed these results. The conclusion made is that the thyroxine-induced rise in basal metabolic rate lowers the critical temperature and reduces the demand for nonshivering thermogenesis. This is reflected in the reduced GDP binding and hence heating capacity of the brown fat mitochondria.

scholarly journals Shear-sensitive adhesion enables size-independent adhesive performance in stick insects

2019 ◽  
Vol 286 (1913) ◽  
pp. 20191327 ◽  
Author(s):  
David Labonte ◽  
Marie-Yon Struecker ◽  
Aleksandra V. Birn-Jeffery ◽  
Walter Federle
Keyword(s):  
Body Weight ◽  
Adhesive Force ◽  
Whole Body ◽  
Small Animals ◽  
Shear Forces ◽  
Stick Insects ◽  
Adhesive Pads ◽  
The Difference ◽  
Large Animals ◽  
Adhesive Performance

The ability to climb with adhesive pads conveys significant advantages and is widespread in the animal kingdom. The physics of adhesion predict that attachment is more challenging for large animals, whereas detachment is harder for small animals, due to the difference in surface-to-volume ratios. Here, we use stick insects to show that this problem is solved at both ends of the scale by linking adhesion to the applied shear force. Adhesive forces of individual insect pads, measured with perpendicular pull-offs, increased approximately in proportion to a linear pad dimension across instars. In sharp contrast, whole-body force measurements suggested area scaling of adhesion. This discrepancy is explained by the presence of shear forces during whole-body measurements, as confirmed in experiments with pads sheared prior to detachment. When we applied shear forces proportional to either pad area or body weight, pad adhesion also scaled approximately with area or mass, respectively, providing a mechanism that can compensate for the size-related loss of adhesive performance predicted by isometry. We demonstrate that the adhesion-enhancing effect of shear forces is linked to pad sliding, which increased the maximum adhesive force per area sustainable by the pads. As shear forces in natural conditions are expected to scale with mass, sliding is more frequent and extensive in large animals, thus ensuring that large animals can attach safely, while small animals can still detach their pads effortlessly. Our results therefore help to explain how nature’s climbers maintain a dynamic attachment performance across seven orders of magnitude in body weight.

scholarly journals Evidence that microtubules do not mediate opsin vesicle transport in photoreceptors.

1989 ◽  
Vol 109 (6) ◽  
pp. 3053-3062 ◽  
Author(s):  
D K Vaughan ◽  
S K Fisher ◽  
S A Bernstein ◽  
I L Hale ◽  
K A Linberg ◽  
...  
Keyword(s):  
Outer Segment ◽  
Lucifer Yellow ◽  
Lateral Displacement ◽  
Linear Increase ◽  
Rod Photoreceptor ◽  
Drug Induced ◽  
Membrane Assembly ◽  
Induced Changes ◽  
Vectorial Transport

The organization of the rod photoreceptor cytoskeleton suggests that microtubules (MTs) and F actin are important in outer segment (OS) membrane renewal. We studied the role of the cytoskeleton in this process by first quantifying OS membrane assembly in rods from explanted Xenopus eyecups with a video assay for disc morphogenesis and then determining if the rate of assembly was reduced after drug disassembly of either MTs or F actin. Membrane assembly was quantified by continuously labeling newly forming rod OS membranes with Lucifer Yellow VS (LY) and following the tagged membranes' distal displacement along the OS. LY band displacement displayed a linear increase over 16 h in culture. These cells possessed a longitudinally oriented network of ellipsoid MTs between the sites of OS protein synthesis and OS membrane assembly. Incubation of eyecups in nocodazole, colchicine, vinblastine, or podophyllotoxin disassembled the ellipsoid MTs. Despite their absence, photoreceptors maintained a normal rate of OS assembly. In contrast, photoreceptors displayed a reduced distal displacement of LY-labeled membranes in eyecups treated with cytochalasin D, showing that our technique can detect drug-induced changes in basal rod outer segment assembly. The reduction noted in the cytochalasin-treated cells was due to the abnormal lateral displacement of newly added OS disc membranes that occurs with this drug (Williams, D. S., K. A. Linberg, D. K. Vaughan, R. N. Fariss, and S. K. Fisher. 1988. J. Comp. Neurol. 272:161-176). Together, our results indicate that the vectorial transport of OS membrane constituents through the ellipsoid and their assembly into OS disc membranes are not dependent on elliposid MT integrity.

scholarly journals Effect of shear forces and ageing on the compliance of adhesive pads in adult cockroaches

2015 ◽  
Vol 218 (17) ◽  
pp. 2775-2781 ◽  
Author(s):  
Y. Zhou ◽  
A. Robinson ◽  
C. Viney ◽  
W. Federle
Keyword(s):  
Shear Forces ◽  
Adhesive Pads

scholarly journals Insect tricks: two-phasic foot pad secretion prevents slipping

2009 ◽  
Vol 7 (45) ◽  
pp. 587-593 ◽  
Author(s):  
Jan-Henning Dirks ◽  
Christofer J. Clemente ◽  
Walter Federle
Keyword(s):  
Adhesive System ◽  
Continuous Phase ◽  
Stick Insect ◽  
Force Measurements ◽  
Friction Forces ◽  
Adhesive Pads ◽  
Foot Pad ◽  
Detailed Function ◽  
Adhesive Secretion

Many insects cling to vertical and inverted surfaces with pads that adhere by nanometre-thin films of liquid secretion. This fluid is an emulsion, consisting of watery droplets in an oily continuous phase. The detailed function of its two-phasic nature has remained unclear. Here we show that the pad emulsion provides a mechanism that prevents insects from slipping on smooth substrates. We discovered that it is possible to manipulate the adhesive secretion in vivo using smooth polyimide substrates that selectively absorb its watery component. While thick layers of polyimide spin-coated onto glass removed all visible hydrophilic droplets, thin coatings left the emulsion in its typical form. Force measurements of stick insect pads sliding on these substrates demonstrated that the reduction of the watery phase resulted in a significant decrease in friction forces. Artificial control pads made of polydimethylsiloxane showed no difference when tested on the same substrates, confirming that the effect is caused by the insects’ fluid-based adhesive system. Our findings suggest that insect adhesive pads use emulsions with non-Newtonian properties, which may have been optimized by natural selection. Emulsions as adhesive secretions combine the benefits of ‘wet’ adhesion and resistance against shear forces.

Functional Morphology and Design Constraints of Smooth Adhesive Pads

MRS Bulletin ◽  
2007 ◽  
Vol 32 (6) ◽  
pp. 479-485 ◽  
Author(s):  
W. Jon. P. Barnes
Keyword(s):  
Fluid Layer ◽  
Adhesive Force ◽  
Average Thickness ◽  
Force Component ◽  
Design Constraints ◽  
Friction Forces ◽  
Adhesive Pads ◽  
Tree Frogs ◽  
Strong Attachment ◽  
Air Liquid Interface

AbstractSmooth adhesive pads are found among the arthropods, amphibians (particularly tree frogs), and in some mammals. They are used for dynamic adhesion when an animal is climbing steep or overhanging smooth surfaces. There is a need for strong attachment to avoid falling and easy detachment to enable the animal to move. This article describes the morphology and physical properties of smooth adhesive pads, stressing how there is little variation in structure, within tree frogs at least, even among pads that have evolved independently. This is clear evidence of an optimum design; best adhesion occurs when there is a continuous, thin film of fluid between the pad and the surface. Smooth adhesive pads adhere by wet adhesion, the main force component being capillarity, produced by the air/liquid interface (meniscus) around the edge of each pad. Smooth adhesive pads also produce substantial friction forces, probably because of actual contact between the pad surface and substrate (tree frogs) or non-Newtonian properties of the secreted fluid (insects). This is possible because the fluid layer beneath the pad has an average thickness of only a few nanometers. The article also discusses the scaling of adhesive force with size and, finally, implications for biomimetics.

scholarly journals Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour

2008 ◽  
Vol 5 (25) ◽  
pp. 845-853 ◽  
Author(s):  
Bryan Schubert ◽  
Jongho Lee ◽  
Carmel Majidi ◽  
Ronald S Fearing
Keyword(s):  
Shear Force ◽  
Strong Dependence ◽  
Adhesive Force ◽  
Shear Forces ◽  
Spherical Probe ◽  
Adhesive Pads ◽  
Normal Adhesion ◽  
Fibre Angle ◽  
First Time ◽  
Adhesion Effect

The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 μm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.

scholarly journals Wetting of the tarsal adhesive fluid determines underwater adhesion in ladybug beetles

2021 ◽  
Author(s):  
Pranav Sudersan ◽  
Michael Kappl ◽  
Bat-El Pinchasik ◽  
Hans-Jürgen Butt ◽  
Thomas Endlein
Keyword(s):  
Capillary Forces ◽  
Smooth Surfaces ◽  
Air Bubble ◽  
Underwater Adhesion ◽  
Wetting Properties ◽  
Adhesive Pads ◽  
Potential Strategy ◽  
Adhesive Fluid ◽  
Adhesive Forces

Many insects can climb smooth surfaces using hairy adhesive pads on their legs mediated by tarsal fluid secretions. It was previously shown that a terrestrial beetle can even adhere and walk underwater. The naturally hydrophobic hairs trap an air bubble around the pads, allowing the hairs to make contact to the substrate like in air. However, it remained unclear to what extent such an air bubble is necessary for underwater adhesion. To investigate the role of the bubble, we measured the adhesive forces inindividual legs of live but constrained ladybug beetles underwater in the presence and absence of a trapped bubble and compared it with its adhesion in air. Our experiments revealed that on a hydrophobic substrate, even without a bubble, the pads show adhesion comparable to that in air. On a hydrophilic substrate, underwater adhesion is significantly reduced, with or without a trapped bubble. We modelled the adhesion of a hairy pad using capillary forces. Coherent with our experiments, the model demonstrates that the wetting properties of the tarsal fluid alone can determine the ladybugs’ adhesion to smooth surfaces in both air and underwater conditions and that an air bubble is not a prerequisite for their underwater adhesion. The study highlights how such a mediating fluid can serve as a potential strategy to achieve underwater adhesion via capillary forces, which could inspire artificial adhesives for underwater applications.

scholarly journals Adhesion-free cell migration by topography-based force transduction

2019 ◽  
Author(s):  
Anne Reversat ◽  
Jack Merrin ◽  
Robert Hauschild ◽  
Ingrid de Vries ◽  
Matthieu Piel ◽  
...  
Keyword(s):  
Actin Cytoskeleton ◽  
Three Dimensional ◽  
Free Cell ◽  
Retrograde Flow ◽  
Shear Forces ◽  
Topographic Features ◽  
Force Coupling ◽  
Integrin Family ◽  
Amoeboid Cells ◽  
Adhesive Forces

AbstractEukaryotic cells migrate by coupling the intracellular force of the actin cytoskeleton to the environment. While force-coupling is usually mediated by transmembrane adhesion receptors, especially these of the integrin family, amoeboid cells like leukocytes can migrate extremely fast despite very low adhesive forces1. We show that leukocytes cannot only migrate under low adhesion but indeed can transduce forces in the complete absence of transmembrane force coupling. When confined within three-dimensional environments, they use the topographic features of the substrate to propel themselves. Here, the retrograde flow of the actin cytoskeleton follows the texture of the substrate, creating shear forces sufficient to drive deformations towards the back of the cell. Notably, adhesion dependent and adhesion independent migration are not exclusive but rather variants of the same principle of coupling retrograde actin flow to the environment and thus can potentially operate simultaneously. As adhesion free migration is independent of the chemical composition of the environment it renders cells completely autonomous in their locomotive behavior.

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