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Artificial mother of pearl made by bacteria

Researchers from the University of Rochester in the US developed an inexpensive and environmentally friendly method for making artificial mother of pearl using bacteria.

Mother of pearl, also known as nacre, is an exceptionally tough, stiff, flexible, iridescent material produced by some molluscs, giving shine to the inside of shells and the outer layer of pearl.

Researcher have managed to recreate nacre before, but those methods typically involve expensive equipment, high temperatures, or toxic chemicals. The new method only involves calcium carbonate, bacteria, and urea (a component of urine).

The impressive mechanical properties of natural nacre come from the hierarchical layered structure. This allows energy to disperse evenly across the material. The Rochester team managed to replicate these layers using two strains of bacteria.

In order to make the artificial nacre, the researchers alternating thin layers of crystallised calcium carbonate and sticky polymer. They combine calcium carbonate with the bacteria Sporosarcina pasteurii and urea. This combination triggers the crystallisation of calcium carbonate. Then, the bacteria Bacillus licheniformis are added, and the material is put in an incubator to create the polymer layer.

Currently, it takes about a day to build up a layer of five millimetres thick.

One of the advantages of the nacre produced this way is that it is biocompatible, which makes it suitable for medical applications like artificial bones and implants. Additionally, the material is stiffer and tougher than most plastics, but also very lightweight, so it could be useful in transportation.

The nacre might even be used to build houses on the moon. The only ingredients necessary would be an astronaut and a small tube of bacteria. There is a large amount of calcium available in moon dust. The astronaut can provide urea, simply by going to the bathroom.

Photos: University of Rochester / J. Adam Fenster

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