Scientists in the United States have discovered how a squid is capable of operating its knife-sharp beak without harming its soft, gelatinous body.

The team of engineers, biologists and marine scientists at the University of California, Santa Barbara, report that a gradual change in stiffness is the answer.

The beak of the Humboldt squid is sharp and hard at the tip and soft "like Jell-O" at the base.
(Science)

Squids use their sharp beaks, one of the hardest materials found in nature, to slice through the spinal cords of their prey, fish, and defend themselves against sperm whales, their main predator other than humans.

The beaks attach to the soft tissue inside the squid's mouth and as such has made researchers question why the squids don't get cut every time they attack a fish.

"Here you have a 'cutting tool' that's extremely hard and stiff at its tip and is attached to a material — the muscular buccal mass [the soft tissue of the squid's mouth] — that has the consistency of Jell-O," said study co-author Frank Zok, a professor at the university's Department of Materials, in a release.

"You can imagine the problems you'd encounter if you attached a knife blade to a block of Jell-O and tried to use that blade for cutting. The blade would cut through the Jell-O at least as much as the targeted object."

To solve the mystery, the research team painstaking studied the chemical composition of the sharp beak of the Humboldt squid. They found that the components in the beak — polysaccaride chitin, water and protein enriched in the compound Dopa and amino acid histidine — slightly change in quantities between the tip and the base. Dopa is concentrated at the tip, and gradually decreases as it moves toward the beak, the researchers found.

When mixed with water, the beak becomes increasingly soft and bendable as it moves toward the mouth. However, when the base dries out, it becomes as stiff as the tip.

"Nature takes care of the problem by changing the beak composition progressively, rather than abruptly, so that its tip can pierce prey without harming the squid in the process," Zok said. "It's a truly fascinating design!"

Could "revolutionize" ways to attach materials 

The findings can find practical application in the field of engineering, the researchers said. Most structures are made by joining very different materials, such as ceramics, metals and plastics, but to do so requires using attachments such as nails or adhesives.

Zok said this type of joining poses limitations, but if scientists could reproduce the kind of gradations found in squid beaks "it would open new possibilities" for joining materials.

"For example, if you graded an adhesive to make its properties match one material on one side and the other material on the other side, you could potentially form a much more robust bond," he said. "This could really revolutionize the way engineers think about attaching materials together."

The findings are published in the March 28th edition of the journal Science.