Sharp Beaks Stick to Soft Squid
Could you carve a roast dinner using a knife that had no handle? Well this is almost what a squid has to do every time it uses its beak. Scientists at the University of California at Santa Barbara have discovered how a squid's sharp, hard beak attaches to its soft, squidgy body, leading the way for new materials which can perform more than one task.
Squid beaks are very strong; in fact it's one of the hardest and stiffest wholly organic materials known. But it's never been fully understood how this stiff, hard material can attach to the soft material that makes up most of the squid's body. In order to bite down on prey, the beak will exert huge forces on to the soft skin, and - like carving a roast using a knife with no handle - should do almost as much damage to the squid as it does to its prey.
Writing in Science, Ali Miserez and colleagues spotted a clue in the colour of the beak - it fades from black at the tip to almost transparent near where it attaches to the body. They took slices through the beak of the Humboldt Squid, Dosidicus gigas to look at how things change as you go along this colour gradient. By using different chemicals to remove either the proteins or pigments, they noticed a distinct gradient in the amount of water, chitin (which is a bit like the protein Keratin - which makes up horns and fingernails) and proteins which include a substance called Dopa - as you go along the beak.
So the very tip, the sharpest, stiffest bit of the beak, called the rostrum, there is far more dopa-containing protein - and these are able to form cross bonds to make the rostrum much tougher. As you move away from the tip, the amount of protein decreases, but the amount of both chitin and water greatly increases.
This is a great example of nature joining together two mis-matched materials, so we can learn from nature's example and use these techniques to attach biologically active components to materials. So we can develop better anti-fowling coatings for boats, but also new and better ways to test how biological systems will react to chemicals. In fact, knowing how dopa polymerizes has already helped to develop mussel-inspired glue, and should allow us to attach multi-functional coatings on to almost any surface.