Churchgoers took to the streets for the Walk of Witness in Perth yesterday, starting and finishing at St John’s Kirk. Picture: Phil Hannah.

RESEARCH: Study reveals how outer shells can be strong but weak enough for chicks to break

Scientists believe they have cracked the conundrum of how chicken eggs are strong enough to resist being fractured from the outside, but weak enough to be broken from the inside when the chick hatches.

A Canadian study found that eggshells develop to be strong, but also not too weak because of changes in their nanostructure which occur during the egg’s incubation.

Researchers believe that a better understanding of events that drive eggshell hardening and strength could have important implications for food safety.

The team from McGill University in Montreal used new techniques to expose the interior of the eggshells to study their molecular nanostructure and mechanical properties. They said birds have benefited from millions of years of evolution to make the perfect eggshell – a thin, protective biomineralised chamber for embryonic growth that contains all the nutrients required for the growth of a baby chick.

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, the team found that this dual-function relationship is possible thanks to minute changes in the shell’s nanostructure which occurs during egg incubation.

Professor Marc McKee said: “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.

“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.”