The avian eggshell is a multilayered structure, which is comprised of 95% calcium carbonate in the form of calcite and approximately 3.5% organic matrix consisting of proteins, glycoproteins and proteoglycans.  The eggshell plays a critical role in protecting the egg contents from physical insult and bacterial penetration and as such its strength and simplicity have become iconic in bioengineering and biotechnology. The success of the structure relies on the interplay of crystalline material and biomolecules at a number of structural levels and it is believed that factors such as nutrition, housing and environmental stresses can affect the physiology of the oviduct and thus the quality of the eggshell.

The exact role of the eggshell specific proteins in shell formation is unclear, although they are thought to influence nucleation, control crystal growth and shape, and play a role in the mechanical properties of the eggshell. Recent advances have focused on determining the relationship between the proteins and shell microstructure, and the overall effects on the structure / function relationship of the resulting eggshell. Insight into these factors is essential if an improvement in eggshell quality is to be effected.

This article describes how modern biotechnology has improved our understanding of the key processes in the generation of the calcitic shell.