Biomimetic Self-Organization and Self-Healing - Engineered Biomimicry - page 337

FIGURE 13.8 The plug formation and sealing process in blood coagulation. Left: Platelets in contact with collagen fibers
for the plug. Right: A hole is sealed using a clot of fibrin fibers.

FIGURE 13.9 Simplified principle of the first steps in coagulation. When the two agents A and B are in contact with each
other, they form a plug.

means, as shown in Figure 13.9 . A central part of
the sequence of actions in clotting is when a sub-
stance (platelets = agent A) is being exposed to
another substance (collagen fibers = agent B) that
causes a reaction (the platelets get sticky and
plug the hole). A possible application of such a
sealing process could be sealing bicycle and car
tires. The tire could be made as a double-layer
structure. A liquid agent placed between the lay-
ers would react and cure on exposure to air.
Another possible application could be sealing of
leaking gas pipes in which an external coating
could swell when exposed to the gas.
Researchers at the University of Illinois work
with self-healing of polymers and composites
that is inspired by blood clotting in animals
[35, 36] . Three different approaches are used in
this research: (1) capsule based, (2) vascular, and

(3) intrinsic. The basic idea in the capsule-based
and the vascular approaches is to include two
different and isolated chemical agents in the
material; these agents can interact with each other
at a microscopic level when damage occurs. In the
first approach, the two chemical agents are con-
tained in microscopic capsules or spheres. In the
vascular approach, the agents are held in separate
hollow channels or capillaries. The intrinsic
approach designates materials that have latent
self-healing functionality that is activated by the
damage or an external stimulus. Examples of
basic mechanisms are reversible polymerizations,
melting of thermoplastic phases, hydrogen bond-
ing, and ionic interactions. Toohey and colleagues
reported making a coated material that repeat-
edly can repair cracks in a surface coating [37] . A
ductile base material with a three-dimensional