Page 366 - Biomimetics : Biologically Inspired Technologies

Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c013 Final Proof page 352 21.9.2005 11:51pm

352 Biomimetics: Biologically Inspired Technologies

tough since the Palauan people of the south Pacific squeeze the sea cucumber until it squirts out its
sticky threads, which they put on their feet to protect them when they walk around the reef.
When attacked, the centipede Henia rolls itself up with its ventral surface facing outward. This
is the opposite to most centipedes, which either attack with their large mandibles or roll up with
their dorsal surface — the most armored — facing outward. However, Henia has a large gland on
the underside of each segment which secretes an adhesive. The amount of adhesive is more than
10% of the body weight. The adhesive sticks to the mouthparts, etc., of the assailant preventing the
parts from working. While, the assailant retires to clean itself, the centipede escapes. The glue
seems to be made of two components: a fibrous protein (possibly silk-like) and a globular protein,
which is the actual adhesive. At high magnification, the adhesive appears as a large number of fine
fibres stuck firmly at each end. Thus removing the adhesive is not as simple as initiating a crack and
propagating it; each fibre has to be broken separately, taking a lot of time and effort (Hopkin et al.,
1990). The adhesive can stick to dirty wet surfaces, desirable for any technical adhesive. When
sticking two glass plates together it is as effective as a cyanoacrylate adhesive.

13.4.3 Sticky Foam

A name given to a polymer-based superadhesive agent. The technology first began appearing in
commercial applications such as ‘‘super glue’’ and quick setting foam insulation. It is extremely
persistent and is virtually impossible to remove. Sticky foam came to public attention on February
28, 1995 when U.S. Marines used it in Mogadishu, Somalia, to prevent armed intruders from
impeding efforts to extricate United Nation forces from that country (Alexander et al., 1996).
A foam allows a limited amount of material to occupy a greater volume, and since the intent is to
impede rather than to entrap, the greater difficulty of breaking a structure that can accommodate
higher strains, and is made of multiple threads, contributes to the effectiveness of the mechanism.
This is probably why it occurs in the adhesive plaque which sticks the byssus thread of the mussel
onto the rock. Otherwise, foams in biology are more used for protection than for attack and are an
integral part of many egg cases, especially in snails and insects (e.g., Mantis, Locusta). They are
commonly made of protein, often phenolically tanned and waterproofed, although their primary
stability comes from their liquid crystalline structure (Neville, 1993)

13.4.4 Rope

Nylon rope dispersed by a compressed air launcher mounted on a truck (Alexander et al., 1996).
With animals the rope can become part of an entrapment mechanism — basically with an
adhesive device on the end of the rope. Examples are the ballistic snares of the chameleon and the
squid.
In the arms of the squid, transverse muscle provides the support required for the relatively slow
bending movements while in the tentacles the transverse muscle is responsible for the extremely
rapid elongation that occurs during prey capture. In the squid Loligo pealei, the thick filaments of
the obliquely striated muscle fibres of the arms are approximately 7.4 mm long while those in the
cross-striated fibres of the tentacle are approximately 0.8 mm long. This results in more series
elements per unit length of fibre. Since shortening velocities of elements in series are additive, this
results in the shortening velocity of the tentacle fibres to be approximately 15 L 0 s 1 compared with
the arm transverse muscle 1.5 L 0 s 1 at 198C.
The strike of L. pealei when it is capturing its prey takes as little as 20 ms. During the strike, the
proximal portion of the tentacle, the stalk, elongates. The nonextensible distal portion of the
tentacle, the club, contacts the prey and attaches using suckers. Extension takes 20 to 40 ms with
1
peak strains in the stalk of 0.43 to 0.8. Peak longitudinal strain rates vary from 23 to 45 s . The
2
stalk can extend at over 2 ms 1 at an acceleration of 250 ms . Once the tentacular clubs have
contacted the prey, the stalks often buckle (Kier and Thompson, 2003).