MASTER THESIS Biomimetic potential of sponge ... - IAP/TU Wien

than the Griffith criterion, it has been proposed that nano-scale of minerals in biocomposites
is the result of selection for fracture strength and robustness (Gao et al., 2003).
Figure 8: Hierarchical architecture. These two landmark buildings of Paris epitomize the benefits but also the
practical difficulties when it comes to man-made hierarchical architecture. The Eiffel tower (c) has been
erected 1887-89 and, at least according to Mandelbrot (1983), Gustave Eiffel perceived the advantage of
building his most famous edifice as a third order hierarchical structure: its relative density is approximately
fivefold lower than the first order hierarchical structure of far more modern buildings like the Pompidou Centre
(a). Counterintuitive as this may seem, it might well be because practical reasons (cost of fabrication and
maintenance) still outweigh the material savings (Lakes, 1993). (b) Strength of a structure rises with
hierarchical order, explaining why nature has adopted this principle for virtually all biominerals; a trend that we
might want to adopt for smarter engineering; be it in the building industry or in nanotechnology. ©
conservapedia.com (a) and (Lakes, 1993) (b)
Man-made vs. natural architecture
In man-made structures, hierarchical structure is not always intentional. The structure of
the Eiffel Tower in Paris can be assigned hierarchy of level three (Figure 8c): the overall
structure is composed of shorter diagonal and horizontal struts, which reveal their ordered
inner life at a closer look.
Mandelbrot (1983) has suggested this hierarchical structure to be intended by the architect,
as it conveys the same mechanical stability of a first order hierarchical structure (Figure 8a)
at a mere 20% of its weight. Others, however, asserted more practical reasons why Eiffel
might have opted to use short trusses, like the relative ease of construction (Harriss, 1975).
Even if Eiffel had deliberately made use of the principle of hierarchy; in modern structural
engineering it does not seem to find favour (Figure 8a). This is largely due to high cost of
construction and maintenance (Lakes, 1993). Trivial as this reason might seem, it reflects a
fundamental difference between natural and man-made construction. Vincent (2008)
summarized this observation as follows:
“In materials-processing nature replaces the massive use of energy (for example high
temperatures or harsh chemical reactions,) with the use of information (which equates with
structure at all levels”
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