Biomimetic Self-Organization and Self-Healing - Engineered Biomimicry - page 339

FIGURE 13.11 A self-sealing principle. The higher pressure within the foam cells causes the foam to expand into punc-
turing fissures. Drawing based on Ref. 39 .

To illustrate the practical implication of the
repair efficiency, Rampf and colleagues provide
the following example. If a medium-sized rub-
ber boat with a conventional membrane is punc-
tured with a 2.5 mm spike, it would take about
26 min for the pressure to drop from 500 to 100
mbar, which is considered the limit for safe use.
Using a foam-coated membrane with a repair
efficiency of 0.99 instead would increase the
time for the pressure drop to about 43 h, i.e., by
a factor of 100.
Some animals employ a drastic antipredator
strategy that also involves a self-sealing action.
They self-amputate parts of themselves (also
called autotomy ) as a last resort. The best-known
example comes from lizards that readily let go
of their tails when the tails are grabbed by pred-
ators. However, most of the animals that display
autotomy are invertebrates from almost all taxo-
nomic groups [43] . Autotomy has evolved inde-
pendently many times because the costs
associated with the loss of an appendage are far
outweighed by the advantage of staying alive.
However, common to all groups is that autotomy
occurs along predefined breakage lines, such as
between specific leg joints in spiders or at the
tail root in lizards [43] . The predefined breaking
plane is particularly weak and gives a clean
break with minimal external force, which
ensures that the amputation is followed by a
minimal loss of blood and in many cases also
facilitates the ensuing regeneration. Sometimes,

autotomy in lizards does not happen at the
joints between two vertebrae but by bone frac-
ture [44] . The core principles are illustrated in
Figure 13.12 based on the description in Ref. 44 .
A fracture along a breaking plane in one of the

FIGURE 13.12 Simplified sketch of a basic principle in
autotomy, i.e., self-amputation, seen in some lizards. When
certain muscles contract, one of the vertebrae breaks along
a predefined fracture line. When the predator pulls the tail,
the tissue is torn along weak planes. The drawing is based
on the description of autotomy in Ref. 44 .