Feat of clay is a pearl

Nature always does things for a reason, and it's hardly ever just to look pretty.

Humans might use mother-of-pearl in jewellery, but to the oyster that made it, it's near-perfect armour - flexible, smooth, and extremely tough. Researchers from Oklahoma State University, although hundreds of miles from any oyster beds, have developed a material which mimics the properties of the mother-of-pearl, which is more properly known as nacre. They believe that it might find uses as a lightweight composite in aircraft and artificial bone.

Nacre's properties arise from its structure, which is similar to a nanoscale brick wall. Calcium carbonate 'bricks' are embedded in layers of pliable protein 'mortar'. The Oklahoma researchers, led by Nicholas Kotov, copied the structure using a negatively-charged clay, montmorillonite, as the bricks and a positively-charged polyelectrolyte, poly(diallyldimethylammonium) chloride, PDDA, as the mortar.

Kotov's team made the artificial nacre by dipping a glass slide in alternating baths of clay dispersed in water and a solution of the polymer. The resulting film, though thin, is very strong and flexible and has the characteristic iridescence of natural nacre. 'It is a very robust preparation and produces beautiful layers every time,' says Kotov.

The researchers are now refining the manufacturing technique, and working on the effect of adding chemicals to give the material resistance to ultraviolet light and corrosion.