Cracking eggshell nanostructure
The findings, reported today in Science Advances, could have important implications for food safety in the agro-industry.
Birds have benefited from millions of years of evolution to make the perfect eggshell, a thin, protective biomineralized chamber for embryonic growth that contains all the nutrients required for the growth of a baby chick. The shell, being not too strong, but also not too weak (being 鈥渏ust right鈥� Goldilocks might say), is resistant to fracture until it鈥檚 time for hatching.
But what exactly gives bird eggshells these unique features?
To find out, Marc McKee鈥檚 research team in 海角社区鈥檚 Faculty of Dentistry, together with Richard Chromik鈥檚 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.
鈥淓ggshells 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,鈥� says McKee, who is also a professor in 海角社区鈥檚 Department of Anatomy and Cell Biology.
鈥淭hanks to a new focused-ion beam sectioning system recently obtained by 海角社区鈥檚 Facility for Electron Microscopy Research, we were able to accurately and thinly cut the sample and image the interior of the shell.鈥�
Eggshells are made of both inorganic and organic matter, this being calcium-containing mineral and abundant proteins. Graduate student Dimitra Athanasiadou, the study鈥檚 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.
A glimpse into egg biology
The results also provide insight into the biology and development of chicken embryos in fertilized and incubated eggs. 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.聽 Using atomic force microscopy, and electron and X-ray imaging methods, Professor McKee鈥檚 team of collaborators found that this dual-function relationship is possible thanks to minute changes in the shell鈥檚 nanostructure that occurs during egg incubation.
In parallel experiments, the researchers were also able to re-create a nanostructure similar to that which they discovered in the shell by adding osteopontin to mineral crystals grown in the lab. Professor McKee believes that 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.
鈥淎bout 10-20% of chicken eggs break or crack, which increases the risk of Salmonella poisoning,鈥� says McKee. 鈥淯nderstanding 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.鈥�
This work was primarily supported by grants from the Natural Sciences and Engineering Research Council and the Canadian Institutes of Health Research.
鈥淣anostructure, Osteopontin and Mechanical Properties of Avian Calcitic Eggshell,鈥� by D. Athanasiadou et al., Science Advances
To contact the researcher directly: marc.mckee [at] mcgill.ca
