Author: Laurel Hamers / Source: Science News
A chicken eggshell has a tricky job: It must protect a developing chick, but then ultimately let the chick break free.
The secret to its success lies in its complex nanostructure — and how that structure changes as the egg incubates.Chicken eggshells are about 95 percent calcium carbonate by mass. But they also contain hundreds of different kinds of proteins that influence how that calcium carbonate crystalizes. The interaction between the mineral crystals and the proteins yields an eggshell that’s initially crack-resistant, while making nanoscale adjustments over time that ultimately let a chick peck its way out, researchers report online March 30 in Science Advances.
Researchers used a beam of ions to cut thin cross sections in chicken eggshells. They then analyzed the shells with electron microscopy and other high-resolution imaging techniques. The team found that proteins disrupt the crystallization of calcium carbonate, so that what seems at low resolution to be neatly aligned crystals is actually a more fragmented jumble. This misalignment can make materials more resilient: Instead of spreading unimpeded, a crack must zig and zag through scrambled crystals.
While a chicken eggshell is only about a third of a millimeter thick, its nanoscale structure isn’t consistent throughout. Nanostructures toward the outside of the shell (A) are smaller than those on the inside of the shell (B and C, moving farther inward), perhaps conferring increased…
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