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Nanostructures and a binding protein create a shell strong enough to protect a chick but soft enough for it to hatch.
An eggshell is tough enough to protect a growing chicken, but softens as hatching time approaches so that the chick can pierce the shell. To investigate how shells strike that balance, Marc McKee at McGill University in Montreal, Canada, and his colleagues studied osteopontin, a protein that binds calcium carbonate in the shell.