Die Muschel Pinna
nobilis.
(Bild:
Biodiversity Heritage Library, CC BY 2.0, via Wikimedia Commons*)
(December 9, 2015) FAU
researchers show how mother-of-pearl is formed from nanoparticles
Materials scientists at FAU have shown for the first time
that the mother-of-pearl in clam shells does not form in a crystallisation
process but is a result of the aggregation of nanoparticles within an organic
matrix. This could lead to a better understanding of the structure of
biomaterials which may be useful in the development of new high-performance
ceramics. The findings of the research group led by Prof. Dr. Stephan E. Wolf
have been published in the latest issue of the renowned journal Nature
Communications (doi: 10.1038/ncomms10097).
Prof. Wolf and his team used a special technique to
investigate the structure of mother-of-pearl. Using a diamond wire saw, they
cut a 60-centimetre wedge out of the shell of a large Pinna nobilis – a type of
clam found in the Mediterranean – which they then polished using a novel method
before examining it under a scanning transmission electron microscope. ‘We
borrowed the wedge-polishing technique from the semiconductor industry,’
Stephan Wolf explains. ‘This method makes it possible to look at extremely
large areas, something that was very difficult to do before.’
Traditional model
disproved
The high-resolution images from the scanning transmission
electron microscope showed that the structure of the shell is very
heterogeneous – from irregular calcite prisms on the outside to the smooth
mother-of-pearl on the inside of the shell, with an organic layer in the
middle. ‘The transition from the organic to the mother-of-pearl layer is
particularly interesting,’ Stephan Wolf says. ‘Here we find the first
nanoparticles of between 50 and 80 nanometres in size that aggregate more and
more as they get closer to the inside of the shell and merge to form
mother-of-pearl platelets, finally forming the highly structured
mother-of-pearl that we all know.’
Prefabrication in
nature
With their findings the Erlangen-based researchers have
shown for the first time that mother-of-pearl does not form through a
crystallisation process in which atoms or ions in a saturated solution are
deposited successively – as previously thought – but instead forms through the
aggregation of prefabricated nanocrystals. ‘If we compare the growth process of
mother-of-pearl to building a house, the clam uses a kind of prefabricated
construction method, while crystallisation is like building a wall out of
individual bricks,’ Stephan Wolf explains.