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

description of the steps involved in the synthesis of biogenic nacre and the control for all
relevant parameters in the macroscopic biomimetic replica seem to be on an advanced level
compared to efforts regarding siliceous spicules (Wang et al., 2012c) (Wang et al., 2012b)
(André et al., 2012) (Voznesenskii et al., 2010).
Synthesis of artificial nacre has long been envisaged (Sellinger et al., 1998) (Tang et al.,
2003). Hallmark properties of this biomineral are its remarkable strength and toughness as
well as its iridescence (Figure 21c) (Smith et al., 1999). Nacre is a layered structure with
alternating layers of aragonite (CaCO 3 ) and thin organic membranes in a brick-and-mortar
fashion. As reviewed by (Mayer, 2005) there are at least ten different mechanisms
contributing to energy dissipation, and hence toughness, of nacre. Among these are
mechanisms also found in sponge spicules, like crack diversion at organic interlayers and the
creation of new surfaces by cracking and delamination (Kamat et al., 2000), as well as
various nacre-specific mechanisms.
Earlier attempts to copy the “structure-function harmony of nacre” (Tang et al., 2003)
include a nanostructured nacre presented be these authors. Various mechanical properties
of the artificial thin film, like tensile strength, were similar to that of nacre. However, like
other attempts in the last decade (Bonderer et al., 2008), base materials far less abundant
than CaCO 3 (e.g., montmorillonite clay) were used. More decisive however was the lack of a
complete implementation of the structural features that make the mechanical properties of
nacre so remarkable. In the aforementioned, clay-based artificial nacres as well as in
attempts with CaCO 3 (e.g., (Wei et al., 2007) the horizontal connection between mineral
layers was not implemented. These connections are essential to establish a nacre-typical
microstructure and accordingly the typical mechanical properties (Finnemore et al., 2012).
In the publication of the most recent attempt (Finnemore et al., 2012) a surprisingly
short list of steps, which are essential to mimic the synthesis of nacre was included:
(i) stabilize amorphous CaCO 3 precursor in solution
(ii) specifically aggregate these and form a continuous film on an organic
surface
(iii) deposit a porous, functionalized thin organic layer on the continuous
mineral film
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