3D imaging leads to discovery of how wet fibers attach to the shell mineral in avian eggshell attachment

How does biology intersect with geology in nature to securely attach wet, slippery organic fibers to a thin layer of rock? The results of a study led by principal investigator Marc McKee published in iScience discovered exactly how the wet fibers attach to the shell mineral, which is a difficult challenge in biology. The team discovered a mineral spiking "nailing" process that forms a robust interfacial mechanical attachment whereby soft organic fibers incorporate in bulk into the shell, and the shell in turn sends mineral nanospikes into the soft, slippery fibers to nail them securely in place so that they do not slip and slide within the shell. 

The research team was able to make this discovery through new advanced 3D imaging electron microscopes they now have at McGill. “Until now, no one had the ability to peer inside this interface in three dimensions to visualize the interlocking phenomenon between two dissimilar substances: hard biorock and a soft fibrous membrane. No one had even thought about how this interface might be secured” says McKee. The discovery of a nanospiking process accounts for an order-of-magnitude increase in surface area for attachment. It was previously thought that the two layers simply touched against one another with a little bit of fiber interdigitation into mineral. With 3D imaging the team was able to see the intricate details of just how they interface, showing the morphological attachment mechanism (nanoscale spiking/"nailing") to measure the exact attachment surface area.

Attachment key to chick development and food safety

The attachment of the fibres to the shell is important because in a fertilized incubated egg the bonding of two dissimilar materials, the membrane which is soft and fibrous and the shell which is hard and crystalline, is required for successful embryonic skeletal growth and chick hatching. If the attachment fails, the chick does not hatch. A robust attachment also has important implications for food safety as table eggs from birds, especially from chickens, are a major global food source. The attachment interface serves as a barrier to pathogens that if compromised may contaminate the egg.

“Many people will never think the same way again about the eggs they have eaten so many times for breakfast whole or else in a recipe, or otherwise. Now, every time they peel or crack an egg they will see and know how the membrane of that breakfast egg links to the shell” says McKee.

Read more in McGill's press release on the study: www.mcgill.ca/newsroom/channels/news/new-understanding-avian-eggshell-attachment-355398

About the study

Attaching organic fibres to mineral: The case of the avian eggshell by Daniel J. Buss, Natalie Reznikov, and Marc D. McKee published in iScience 

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