Last updated April 12, 2018 at 2:15 pm
The nanostructure and mechanical properties of eggs makes them one tough shell to crack.
Eggshells in Prof McKee’s lab. Credit: Laurie Devine, McGill University
How good are you at cracking eggs? Do you use two hands or have you mastered the one-handed crack? The task of cracking the shell is even more remarkable for hatching chicks when they break out from the inside.
Researchers have put their brains together, and put all their eggs in one basket so to speak. The study was an interdisciplinary collaboration between Marc McKee’s research team in McGill’s Faculty of Dentistry and Richard Chromik’s group in Engineering.
They wanted to study the molecular nanostructure and mechanical properties of eggshells. Their findings could have important implications for food safety.
Egg-cellent composition
Everything about eggshells from the shape to the composition has been perfected over millions of years. It’s a thin, protective biomineralised chamber for embryonic growth with all the essential nutrients for the growth of a baby chick.
Using new techniques, they cracked it. Shell strength is determined by the presence of nanostructured mineral associated with osteopontin, an eggshell protein also found in bone.
“Eggshells are notoriously difficult to study by traditional means, because they easily break when we try to make a thin slice for imaging by electron microscopy,” says McKee, who is also a professor in the Department of Anatomy and Cell Biology.
“Thanks to a new focused-ion beam sectioning system recently obtained by McGill’s Facility for Electron Microscopy Research, we were able to accurately and thinly cut the sample and image the interior of the shell.”
Chicken and egg biology
Fertilised chicken eggs are hard when laid and during brooding so that they don’t break. As the chick inside the eggshell grows, it needs calcium to form its bones. During incubation, the inner portion of the shell dissolves to provide calcium, which also weakens the shell, making it easier for a hatching chick to peck its way out.
Using atomic force microscopy, and electron and X-ray imaging methods, the researchers found that this dual-purpose functionality was due to changes in the shell’s nanostructure during egg incubation.
They also re-created a nanostructure similar to what they found in the shell by adding osteopontin to mineral crystals grown in their lab. These nanostructures could go on to influence nanomaterials in material science.
Credit: Carla Schaffer/ AAAS
Unscrambling food safety concerns
The role of proteins in the calcification events that drive eggshell hardening and strength through biomineralisation could have important implications for food safety.
“About 10-20% of chicken eggs break or crack, which increases the risk of Salmonella poisoning,” says McKee. “Understanding how mineral nanostructure contributes to shell strength will allow for selection of genetic traits in laying hens to produce consistently stronger eggs for enhanced food safety.”
The research is published in Science Advances.
