WASHINGTON, March 30 (Xinhua) -- Fertilized chicken eggs manage to resist fracture from the outside, but are weak enough to break from the inside during chick hatching. How could that happen?
A study led by McGill University scientists revealed that it's all in the eggshell's nanostructure.
The findings, reported on Friday in the journal Science Advances, could have important implications for food safety in the agro-industry.
Bird's eggshell is a thin, protective biomineralized chamber for embryonic growth that contains all the nutrients required for the growth of a baby chick. The shell, not too strong, but also not too weak, keeps resistant to fracture until it's time for hatching.
Marc McKee's team in McGill's Faculty of Dentistry, together with Richard Chromik's group in Engineering and other colleagues, used new sample-preparation techniques to expose the interior of the eggshells to study their molecular nanostructure and mechanical properties.
Eggshells are made of both inorganic calcium-containing mineral and abundant organic proteins.
Dimitra Athanasiadou, the paper's first author, found that a factor determining shell strength is the presence of nanostructured mineral associated with osteopontin, an eggshell protein also found in composite biological materials such as bone.
Eggs are sufficiently hard when laid and during brooding to protect them from breaking. As the chick grows inside the eggshell, it needs calcium to form its bones.
During egg incubation, the inner portion of the shell dissolves to provide this mineral ion supply, while at the same time weakening the shell enough to be broken by the hatching chick.
Using atomic force microscopy, and electron and X-ray imaging methods, they found that this dual-function relationship is possible thanks to minute changes in the shell's nanostructure that occurs during egg incubation.
According to McKee, a better understanding of the role of proteins in the calcification events that drive eggshell hardening and strength through biomineralization could have important implications for food safety.
"About 10-20 percent of chicken eggs break or crack, which increases the risk of Salmonella poisoning," said 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."