Page 27 - Biomimetics : Biologically Inspired Technologies

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Introduction to Biomimetics 13

squeezed in the required direction. Such pumping is common in the digestion system. Pumping via
valves and chambers that change volume is found in human and animal hearts, with expansion and
contraction of chambers. The use of one-way valves is the key to the blood flow inside the veins,
where the pressure is lower.

1.5.2.4 Controlled Adhesion

Controlled adhesion is achieved by many organisms using a highly fibrillated microstructure. The
Hemisphaerota cyanea (a beetle) uses wet adhesion that is based on capillary interaction (wet
adhesion) (Eismer and Aneshansly, 2000). The gecko exhibits remarkable dry adhesion using
van der Waals forces. Even though these forces provide low intrinsic energy of approximately
2
50 mJ/m , their effective localized application allows for the remarkable capability (Autumn et al.,
2002). Using this adhesion mechanism, the gecko can race up a polished glass at a speed of
approximately 1 m/sec and support its body weight from a wall with a single toe. Geckos have
millions of 10 to 20 mm long setae, which are microscopic hairs at the bottom of their feet. Each
seta ends with about 1000 pads at the tip (called spatulae) that significantly increase the surface
density, and allow getting into close contact with the adhered surface. This capability motivated
efforts to mimic the gecko adhesion mechanism, and some limited success was reported. Re-
searchers like Autumn and Peattie (2003) sought to develop artificial foot-hair tip model for a dry,
self-cleaning adhesive that works under water and in a vacuum. Their limited success effectively
created a synthetic gecko adhesive that can potentially operate in vacuum areas of clean rooms as
well as outer space.

1.5.2.5 Biological Clock

The body processes are controlled by our biological clock and it is amazing in its precision. It is
critical in assuring the timely execution of the genetic code to form the same characteristics for the
given creatures at the same sequence of occurrence at about the same age. The cicada matures for
17 years, after which it lives for another 1-week period. During this week, all cicadas mate, the
females lay eggs, and then they all die. The hatched cicadas then develop for another 17 years and
these synchronized processes are repeated again.

1.5.3 Biologically Inspired Structures and Parts

Parts and structures also have a biological model of inspiration. Some of these are discussed below.

1.5.3.1 Honeycomb as a Strong, Lightweight Structure

Honeycombs consist of perfect hexagonal cellular structures and they offer optimal packing shape.
For the honeybees, the geometry meets their need for making a structure that provides the
maximum amount of stable containment (honey, larvae) using the minimum amount of material
(Figure 1.8). The honeycomb is, for the same reasons, an ideal structure for the construction of
control surfaces of an aircraft and it can be found in the wing, elevators, tail, the floor, and many
other parts that need strength and large dimensions while maintaining low weight. An example of a
control surface part of an aircraft with a honeycomb is shown in Figure 1.9.

1.5.3.2 Hand Fan

Historically, hand fans were one of the most important ways of cooling down during the hot
summer months (Figure 1.10). This simple tool used to be made of feathers, which copy the shape