Gecko-Effect and Smart Adhesion
The “smart adhesion” of gecko is discussed. It is shown that gecko achieves very high adhesion as well as the ability to detach easily at will due to a hierarchical organization of attachment pads. Experimental data and theoretical models are presented. P
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Abstract The “smart adhesion” of gecko is discussed. It is shown that gecko achieves very high adhesion as well as the ability to detach easily at will due to a hierarchical organization of attachment pads. Experimental data and theoretical models are presented. Properties of a biomimetic adhesive tape using the gecko-effect are reviewed.
In the preceding chapters we have studied in detail how roughness affects wetting. Here we will discuss the so-called adaptive or “smart” adhesion between a gecko foot and a solid surface and engineered surfaces that mimic the smart adhesion of the gecko foot. The topic was investigated in detail by Autumn et al. [16], Autumn [15], Gorb [132], and Bhushan and coworkers [37, 47, 48, 52, 181–184].
12.1 Gecko Several creatures, including insects, spiders, and lizards, have a unique ability to cling to and detach from walls using their attachment systems. Although these creatures have different foot morphology, in most cases they have small hairs that cover the surfaces of their feet, called setae. Using setae, animals develop close contact with a substrate that provides enough attachment force to cling to and crawl on a wide range of natural and artificial surfaces. It also provides reversible adhesion, since they retain the ability to remove their feet from the attachment surface at will by peeling. This universal ability for attachment and detachment is called “smart adhesion” [52]. The most advanced attachment ability in lizards is found in the Tokay (T.) gecko or Gekko gecko. This ability was known even in ancient times; almost 2500 years ago the ability of geckos “to run up and down a tree in any way, even with the head downwards” was observed by Aristotle [37]. However, little was understood about the mechanism of this phenomenon until the microscopic hairs covering the gecko’s toe were discovered in the late nineteenth century and a hierarchical morphology of the gecko toe was revealed after the advent of the SEM in the 1950s (Fig. 12.1).
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12 Gecko-Effect and Smart Adhesion
Fig. 12.1. a Tokay gecko looking top-down (left) and bottom-up (right) [16]. The hierarchical structures of a gecko foot; b a gecko foot [16] and c a gecko toe [15]. Each toe contains hundreds of thousands of setae and each seta contains hundreds of spatulae. Scanning electron microscopy (SEM) micrographs two (at different magnifications) of d the setae [126] and e the spatulae [126]. ST seta, SP spatula, BR branch
12.2 Hierarchical Structure of the Attachment Pads
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Table 12.1. Surface characteristics of Tokay gecko feet [37] Component
Size
Density
Adhesive force
Seta
30–130/5–10 length/diameter (μm)
∼14000 setae/mm2
194 μN (in shear) ∼20 μN (normal)
Branch
20–30/1–2 length/diameter (μm)
–
–
Spatula
2–5/0.1–0.2 length/diameter (μm)
100–1000 spatulae per seta
–
Tip of spatula
∼0.5/0.2–0.3/∼0.01 length/width/thickness (μm)
–
11 nN (normal)
The attachment pads of a T. gecko’s feet consist of a complicated hierarchy of structures beginning with lamellae, soft ridges approximate
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