July 5, 2007 | David F. Coppedge

Mother-of-Pearl Inspires Materials Science

It’s not only beautiful, it’s strong.  EurekAlert described how scientists are intrigued by mother-of-pearl, also called nacre, because of its strength: you can drive a truck over it and it will not break.  It is 3,000 times more resistant to fracture than the aragonite from which the oyster makes it.  95% of it self-assembles in the shell, while the organism directs the rest with protein.  The result is “ one of the most efficient mechanisms you can think of”  The oyster uses the protein as mortar for the crystals that are guided into place.
    The article summarizes why this is interesting:

“If you understand how it forms, you could think of reproducing it, producing a synthetic material that’s inspired by nature – a so-called ‘biomimetic’ material,” [Pupa] Gilbert [U of Wisconsin-Madison] explains.  “If we learn how to harness the mechanism of formation, then we could, for example, produce cars that absorb all the energy at the impact point but do not fracture.
    “But from my point of view, it’s most interesting because of the fundamental mechanisms of how it forms – these natural self-assembly mechanisms we are only just beginning to understand.”

Depending on the crystal orientation, portions of the nacre can appear white, dark or gray.  “The overall effect resembles a camouflage pattern, each roughly columnar cluster a slightly different shade.”  The same material coats bits of sand or matter in the shell to produce the pearls that humans prize so highly.
    Research into mother-of-pearl formation could lead down additional paths, the article says: “With further experiments, the researchers hope to test and refine their model as well as examine other biominerals, such as human teeth and the nacre of other species such as pearl oysters, mussels, or nautiluses, to improve their understanding of biomineral formation and assembly.”
    For earlier entries on nacre, see 07/08/2005 and 07/26/2004.

When a shepherd guides sheep into formation, is that self-assembly?  When a drum major keeps a band marching in tight columns, is that self-assembly?  How about when a ribosome directs amino acids into a protein?  Self-assembly is a misnomer when there is an informed process directing elements into position.  Let’s give credit where credit is due.
    The article made no mention of how evolution could produce one of the most efficient mechanisms one could think of.  Maybe it didn’t.  That’s a starting point for a pearl of wisdom.

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