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

Figure 20: Light guiding properties of sponge spicules. Even though light transmission through spicules of
demosponges has been demonstrated to serve a biological purpose (Brümmer et al., 2008), most research on
waveguide properties has been carried out on spicules from glass sponges, where light guiding properties
might be an accidental by-product of the spicular architecture (Aizenberg et al., 2004). (a) shows the first
(Müller et al., 2009a) and (to the best of my knowledge) only demonstration of the waveguide properties of a
demospongial spicule. Other than all known hexactinellid spicules - that act as a high- and low-pass optical filter
with a cut off at 600 nm and 1300-1400 nm (c) and therefore show a characteristic shift from white to red
colour (in (b)) – demospongial spicules do not alter the quality of light (Müller et al., 2009a). However, this
might well be due to the low length of the spicule and not according to structural differences between glass
sponges and demosponges. In (d, magnification 100 x) the axial filament of a glass sponge spicule appears
brighter than the cladding due to increased scattering. (e) shows the lens-shaped distal end of a demospongial
spicule that couples more light into the “waveguide”. (f) Highlighting that light guided in fascicles of glass
sponge spicules is split at fusion sites (fs). © by (Müller et al., 2009a) for (a) and (b), (Müller et al., 2006a) for (c)
and (d), (Müller et al., 2010) for (e) and (f)
In (Figure 20c) two minima of transmittance through the spicule are apparent. These are
due to the presence of bound water in spicules (Galkina et al., 2009) (Wang et al., 2009). The
minima closely correspond to the three absorption lines of water at 970 nm, 1150 nm and
1190 nm (Braun & Smirnov, 1993) whereat the latter two absorption lines cannot be
resolved in the graphic.
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