scholarly journals Sticky Feet: From Animals to Materials

MRS Bulletin ◽  
2007 ◽  
Vol 32 (6) ◽  
pp. 466-472 ◽  
Author(s):  
Costantino Creton ◽  
Stanislav Gorb
Keyword(s):  
Reversible Adhesion ◽  
Water Layers ◽  
Vertical Walls ◽  
Tree Frogs

AbstractMany insects and some larger animals, such as geckos, skinks, and tree frogs, can easily climb vertical walls and even walk on the ceiling. These abilities require a method to attach the feet strongly but reversibly to a variety of surfaces—smooth or rough, hydrophilic or hydrophobic, clean or containing contaminants. This issue of MRS Bulletin examines how fibrils, absorbed water layers, geometry, and other factors make reversible adhesion possible, and how this understanding might be applied to robots and other artificially created structures that can climb walls, walk on ceilings, and get to other hard-to-reach places.

scholarly journals Sliding-induced non-uniform pre-tension governs robust and reversible adhesion: a revisit of adhesion mechanisms of geckos

2011 ◽  
Vol 9 (67) ◽  
pp. 283-291 ◽  
Author(s):  
Q. H. Cheng ◽  
B. Chen ◽  
H. J. Gao ◽  
Y. W. Zhang
Keyword(s):  
Computational Modelling ◽  
Simulation Approach ◽  
Linear Distribution ◽  
Sliding Motion ◽  
Reversible Adhesion ◽  
Vertical Walls ◽  
Strong Attachment ◽  
Pulling Force ◽  
Complete Detachment ◽  
Key Steps

Several mechanisms have been proposed in the literature to explain the robust attachment and rapid, controllable detachment of geckos' feet on vertical walls or ceilings, yet, it is still debatable, which one is ultimately responsible for geckos' extraordinary capabilities for robust and reversible adhesion. In this paper, we re-examine some of the key movements of geckos' spatula pads and seta hairs during attachment and detachment, and propose a sequence of simple mechanical steps that would lead to the extraordinary properties of geckos observed in experiments. The central subject under study here is a linear distribution of pre-tension along the spatula pad induced by its sliding motion with respect to a surface. The resulting pre-tension, together with a control of setae's pulling force and angle, not only allows for robust and strong attachment, but also enables rapid and controllable detachment. We perform computational modelling and simulations to validate the following key steps of geckos' adhesion: (i) creation of a linear distribution of pre-tension in spatula through sliding, (ii) operation of an instability envelope controlled by setae's pulling force and angle, (iii) triggering of an adhesion instability leading to partial decohesion along the interface, and (iv) complete detachment of spatula through post-instability peeling. The present work not only reveals novel insights into the adhesion mechanism of geckos, but also develops a powerful numerical simulation approach as well as additional guidelines for bioinspired materials and devices.

scholarly journals Tree frog adhesion biomimetics: opportunities for the development of new, smart adhesives that adhere under wet conditions

2019 ◽  
Vol 377 (2150) ◽  
pp. 20190131 ◽  
Author(s):  
Fandong Meng ◽  
Quan Liu ◽  
Xin Wang ◽  
Di Tan ◽  
Longjian Xue ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Science And Technology ◽  
Tree Frog ◽  
Theme Issue ◽  
Testing Hypotheses ◽  
Wet Adhesion ◽  
Reversible Adhesion ◽  
Epithelial Structure ◽  
Dry And Wet Conditions ◽  
Tree Frogs

Enlarged adhesive toe pads on the tip of each digit allow tree frogs to climb smooth vertical and overhanging surfaces, and are effective in generating reversible adhesion under both dry and wet conditions. In this review, we discuss the complexities of the structure of tree frog toe pads in relation to their function and review their biomimetic potential. Of particular importance are the (largely) hexagonal epithelial cells surrounded by deep channels that cover the surface of each toe pad and the array of nanopillars on their surface. Fluid secreted by the pads covers the surface of each pad, so the pads adhere by wet adhesion, involving both capillarity and viscosity-dependent forces. The fabrication and testing of toe pad mimics are challenging, but valuable both for testing hypotheses concerning tree frog toe pad function and for developing toe pad mimics. Initial mimics involved the fabrication of hexagonal pillars mimicking the toe pad epithelial structure. More recent ones additionally replicate the nanostructures on their surface. Finally we describe some of the biomimetic applications that have been developed from toe pad mimics, which include both bioinspired adhesives and friction-generating devices. This article is part of the theme issue ‘Bioinspired materials and surfaces for green science and technology (part 2)’.

Natural convection in a rectangular cavity with piece-wise heated vertical walls: multiple states, stability and bifurcations

2002 ◽  
Author(s):  
Vladimir Erenburg ◽  
Alexander Gelfgat ◽  
Eliezer Kit ◽  
Pinhas Z. Bar-Yoseph ◽  
Alexander Solan
Keyword(s):  
Natural Convection ◽  
Rectangular Cavity ◽  
Vertical Walls ◽  
Stability And Bifurcations

Skin and dry adhesion

2018 ◽  
Author(s):  
Changhyun Pang ◽  
Chanseok Lee ◽  
Hoon Eui Jeong ◽  
Kahp-Yang Suh
Keyword(s):  
Material Properties ◽  
Structural Features ◽  
Mechanical Interlocking ◽  
Multi Scale ◽  
Skin Patch ◽  
Reversible Adhesion ◽  
Dry Adhesion ◽  
Close Observation ◽  
Dry Adhesives ◽  
Shed Light

Close observation of various attachment systems in animal skins has revealed various exquisite multi-scale architectures for essential functions such as locomotion, crawling, mating, and protection from predators. Some of these adhesion systems of geckos and beetles have unique structural features (e.g. high-aspect ratio, tilted angle, and hierarchical nanostructure), resulting in mechanical interlocking mediated by van der Waals forces or liquid secretion (capillary force). In this chapter, we present an overview of recent advances in bio-inspired, artificial dry adhesives, and biomimetics in the context of nanofabrication and material properties. In addition, relevant bio-inspired structural materials, devices (clean transportation device, interlocker, biomedical skin patch, and flexible strain-gauge sensor) and microrobots are briefly introduced, which would shed light on future smart, directional, and reversible adhesion systems.

scholarly journals Double-Chain Cationic Surfactants: Swelling, Structure, Phase Transitions and Additive Effects

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 3946
Author(s):  
Rui A. Gonçalves ◽  
Yeng-Ming Lam ◽  
Björn Lindman
Keyword(s):  
Phase Transitions ◽  
Phase Behaviour ◽  
Double Chain ◽  
Scanning Calorimetry ◽  
Alkyl Chains ◽  
X Ray Scattering ◽  
Amphiphilic Compounds ◽  
Liquid Phases ◽  
Lamellar Phases ◽  
Water Layers

Double-chain amphiphilic compounds, including surfactants and lipids, have broad significance in applications like personal care and biology. A study on the phase structures and their transitions focusing on dioctadecyldimethylammonium chloride (DODAC), used inter alia in hair conditioners, is presented. The phase behaviour is dominated by two bilayer lamellar phases, Lβ and Lα, with “solid” and “melted” alkyl chains, respectively. In particular, the study is focused on the effect of additives of different polarity on the phase transitions and structures. The main techniques used for investigation were differential scanning calorimetry (DSC) and small- and wide-angle X-ray scattering (SAXS and WAXS). From the WAXS reflections, the distance between the alkyl chains in the bilayers was obtained, and from SAXS, the thicknesses of the surfactant and water layers. The Lα phase was found to have a bilayer structure, generally found for most surfactants; a Lβ phase made up of bilayers with considerable chain tilting and interdigitation was also identified. Depending mainly on the polarity of the additives, their effects on the phase stabilities and structure vary. Compounds like urea have no significant effect, while fatty acids and fatty alcohols have significant effects, but which are quite different depending on the nonpolar part. In most cases, Lβ and Lα phases exist over wide composition ranges; certain additives induce transitions to other phases, which include cubic, reversed hexagonal liquid crystals and bicontinuous liquid phases. For a system containing additives, which induce a significant lowering of the Lβ–Lα transition, we identified the possibility of a triggered phase transition via dilution with water.

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