Squid-beak mystery: a knife without a handle

	Beak of the Humboldt squid Click here for more information.

Researchers have solved a biomaterials mystery: how does a squid use its sharp, knife-like beak to disable its prey without damaging the muscle in which the beak is embedded, researchers report in the March 27 issue of Science. It’s the same kind of design problem as a knife with no handle, which would be hard to use without cutting yourself. The beak of the Humboldt squid (Dosidicus gigas) is one of the hardest, wholly organic materials known, and a blow with the beak transmits significant forces to the soft tissues that hold it in place. According to Ali Miserez and colleagues, the squid beak can handle these forces because it is stiff and hard at its cutting end but gradually becomes softer and more flexible as it approaches the place where it attaches to the soft muscle tissue. The researchers painstakingly mapped out the specific chemical composition of each section of the beak, matching it to the beak's mechanical properties at each point. The amount of stiffness is controlled by changing ratios of chitin, water, and proteins enriched in the amino acid histidine and a compound called Dopa. In a related Perspective, Phillip Messersmith discusses Dopa's role in other biological structures, and why researchers are interested in using the compound in synthetic materials that mimic the properties of biomaterials.

ARTICLE #16: "The Transition from Stiff to Compliant Materials in Squid Beaks," by A. Miserez; T. Schneberk; C. Sun; F.W. Zok; J.H. Waite at University of California, Santa Barbara in Santa Barbara, CA.