Sea urchins hold building material clues

2012-02-14 08:15

A sea urchin under high magnification shows the parallel calcite crystals structures. (picture provided)

Cape Town - Scientists have discovered that the chalk produced by sea urchins may hold clues to stronger buildings materials.

A team led by Dr Helmut Cölfen from the University of Konstanz in Germany discovered how the marine animals used lime to grow spines that are hard and flexible.

The animals have calcite crystals that are embedded, like bricks in a wall, into a mortar of amorphous lime mixed with small amounts of biological proteins.

When sea urchin spines are broken, they produce a rough surface, yet they are tough because they consist of lime (calcium carbonate). In geological deposits, lime usually forms calcite crystals that have very different properties to sea urchin spines as they break easily along their cleavage planes.

The team used an X-ray technique to reveal that sea urchin spines are actually built like walls of nanometre-sized bricks of calcite crystals which are aligned in parallel. The bricks are glued together with a mortar of non-crystalline lime.

Elastic

The arrangement creates an elastic type of material that absorbs shocks.

"It was a real challenge to separately characterise the crystalline and non-crystalline parts of the spines, because the individual structures are extremely small. We had to combine two very different techniques using thin X-ray beams, one optimised for nanocrystals and the other for amorphous structures," said Aurélien Gourrier of the European Synchrotron Radiation Facility (ESRF) in Grenoble.

The researchers determined that 92% of the spines consist of crystalline calcite and 8% of amorphous lime. The disordered lime is in turn made of 99.9% calcium carbonate into which a tiny 0.1% of proteins are mixed. At a disordered layer thickness of one or two nanometre around the calcite crystals, it ensures that the sting can only be broken with difficulty.

"It is fascinating that nature can turn fragile materials through structuring into high-performance composite materials, that manufacturing has not managed to produce so far," said Cölfen.

His group is collaborating with a two companies to dedicated to producing high-performance concrete, using the discovered technology.

The research was published in the Proceedings of the National Academy of Sciences.
 

- News24