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Flexible minerals: self-assembled calcite spicules with extreme bending strength.

Science (New York, N.Y.) (2013-03-16)
Filipe Natalio, Tomas P Corrales, Martin Panthöfer, Dieter Schollmeyer, Ingo Lieberwirth, Werner E G Müller, Michael Kappl, Hans-Jürgen Butt, Wolfgang Tremel
ABSTRACT

Silicatein-α is responsible for the biomineralization of silicates in sponges. We used silicatein-α to guide the self-assembly of calcite "spicules" similar to the spicules of the calcareous sponge Sycon sp. The self-assembled spicules, 10 to 300 micrometers (μm) in length and 5 to 10 μm in diameter, are composed of aligned calcite nanocrystals. The spicules are initially amorphous but transform into calcite within months, exhibiting unusual growth along [100]. They scatter x-rays like twinned calcite crystals. Whereas natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This remarkable feature is linked to a high protein content. With nano-thermogravimetric analysis, we measured the organic content of a single spicule to be 10 to 16%. In addition, the spicules exhibit waveguiding properties even when they are bent.

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