Sea urchin shell lights the way for optical material

Someday, optical communications and high-speed computing might owe their success to a little ocean creature: the sea urchin. Materials scientists have fabricated a photonic crystal using a piece of the organism’s shell as a template.

For years, researchers have been searching for ways to make photonic crystals with just the right optical properties. These three-dimensional structures, consisting of arrays of microscopic pores arranged in a lattice, reject some wavelengths of light while letting others pass through. This enables the crystals to manipulate light with exquisite precision (SN: 10/4/03, p. 218: Hot Crystal).

Being a highly organized network of microscopic channels, the magnesium calcite shell of the sea urchin has a configuration similar to that of a photonic crystal. Edwin Thomas of the Massachusetts Institute of Technology and his colleagues sought to use a sea urchin skeleton as a mold for making that type of crystal, but the size and spacing of the pores were too large to produce the desired optical properties. So, the team devised a technique for shrinking the network.

The researchers filled the skeleton’s pores with a polymer and dissolved the magnesium calcite. An inverted replica of the urchin structure remained. Next, the researchers heated the polymer, which caused the structure to shrink by 50 percent. Finally, they filled the pores of the shrunken network with the optical material tellurium and etched away the polymer, leaving behind a photonic crystal. They describe the crystal-fabrication technique in the July Advanced Materials.

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