Biomedical Engineering Reference
In-Depth Information
The need to isolate, cut off, and seal the connec-
tion to a certain area is a desired function for
flooded sewers, fire protection in buildings, sta-
bilization of leaking ships, and minimizing the
spreading of contamination or diseases. Inspira-
tion can be found in the way reptiles and inver-
tebrates self-amputate limbs.
Section
13.7
looked at automatic healing phe-
nomena. Most surfaces are exposed to damage
from wear and tear. In many cases, damage
reduces the functionality of the surface, which
then has to be repaired or replaced. If the surface
could repair or heal itself, improved functional-
ity and reduced cost could be achieved. Self-
healing phenomena in nature therefore attract
interest, and one of these is the byssus thread in
sea mussels. The self-healing mechanisms rely
on at least two factors: (1) a distribution of the
impact so that it results in many small cracks,
and (2) metal-ligand bonds that are reversibly
breakable. Today artificial substances that mimic
the byssus-thread behavior have been made at
a laboratory scale.
Section
13.8
treated adaptive growth, which
also is a desirable property for many structures.
Growth normally expands the object while con-
suming energy and resources, but when a
branch is made it will stay there, even when it
is no longer needed. Slime molds have the
remarkable property that they can reabsorb
parts of their bodies when no longer needed and
recycle the material in other parts of the body.
Apparently, the basic principle used to deter-
mine if a part of the body should be strength-
ened or broken down is fairly simple. It is similar
to the principle used by ants to find the shortest
path to a food source. The slime mold has a large
number of vessels that transport liquid to and
from food sources. The vessels that are con-
nected to food sources have a larger flow than
the other vessels. The difference in flow level
determines the fate of the vessel. The principles
from the slime mold are used to make efficient
computer programs for planning networks such
as railroad systems.
Section
13.9
looked at composite nanostruc-
tured materials that are desirable in a broad
range of applications. One area is improvement
of mechanical properties so that stiffness and
hardness are combined with ductility. This could
be for instance, to combine the wear resistance
found in ceramic materials with elastic proper-
ties in metals. However, combining such differ-
ent materials is not an easy manufacturing task.
Therefore, the multilayer structures found in
mussels and snails attract attention. Thin layers
of gel are spread in mussels to act as scaffolds
for a biomineralization process that forms stiff
chalk layers and thin elastic layers. The biologi-
cal process has not yet been mimicked, but other
processes such as freeze casting have been used
on a laboratory scale to make structures that
emulate natural ones.
Apart from improved material properties,
another perspective in producing the nanostruc-
tured composites is to be able to make the mate-
rial for biological spare parts. Nacre is known to
have good compatibility with human tissue.
Another perspective from producing the deli-
cate multilayer structure is to make photonic
architectures that selectively reflect certain
wavebands through interference. The pearles-
cent appearance of nacre is actually an example
of this, as discussed in Chapter 11.
The aim of this chapter was to show how self-
organization and self-healing take place in
nature and can be mimicked in manmade appli-
cations. The eight approaches show that this is
achieved through more localized control of
activities. Key principles for each of the
approaches have been described in simple
graphical illustrations facilitating the further use
of new design activities.
Acknowledgments
Thanks are due to Ça ˘rı Mert Bakirci and Silviu Iosif for
their contributions to the initial literature research and dis-
cussions on self-organizing principles, and to Tomas Benzon
for drawing the illustrations.
