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

Spicules
Glassy spicules have raised the interest of naturalists as early as 1780. However, it would
remain enigmatic for a century what these spicules actually were, i.e. what their biological
origin was. Only after the first oceanographic cruise, the Challenger-expedition 1873-76, this
question could be clarified (Schulze, 1887). Between the two classes of siliceous sponges,
Hexactinellida produce larger and by far more conspicuous silica structures (Figure 6). As
these dwell mainly in the deep sea and near Antarctica it is not surprising that it was – and
still is - a tedious endeavour to explore siliceous spicules, especially in vivo.
There are various physiological functions to sponge spicules (Figure 7), but it is after life,
when spicules of glass sponges have a paramount ecological impact: skeletal elements of
dead glass sponges are a major ecological factor in their habitats. Mats of this biomaterial
line the benthos of extensive areas of the Antarctic sea and thus provide a hard substrate
that other organisms can dwell on (Barthel, 1992) (Leys et al., 2007).
Since siliceous sponges are among the oldest multicellular organisms, their phylogeny is
closely related to the occurrence of skeletons (Uriz et al., 2003). We can only conjecture why
the first skeletal structures were built and have been preserved in evolutionary younger
organisms (fixation by evolution). Rik Huiskes cut right to the chase referring to a different
class of biological material: “If bone is the answer, then what is the question?” (Huiskes,
2000). Considering the manifold functions of sponge spicules, that might well be more
diverse than the functions of bone, the “question”, i.e. what evolution has selected for,
might be similarly complex. A striking example of unexpected evolutionary constraints that
has been discussed controversially relates to the origin of calcareous skeletons. According to
one theory, the first calcium carbonate based skeletons contested to the need to control
intracellular Ca-levels, and only later evolved for other purposes, including structuring of the
body (Kingsley & Watabe, 1982).Though this explanation (exaptation) has been refused by
others (Vermeij, 1989) it shows how complex it is to fully grasp what any biological material
or structure really is (Uriz, 2006).
Structure
Skeletons based on spicules have been very successful throughout more than half a
billion years (Uriz, 2006). Sponges have retained the principle of using small spicules as a
base for the construction of their skeletons. Interestingly, the conservation even includes the
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