Thursday, June 2, 2016

A World from Dust (Plus): DIY Squid Beak

The squid beak is as sharp and tough as a knife, yet it contains no metal. How could such an amazing structure ever have evolved? The answer is it's surprisingly simple to make a material like squid beak in six words: "by oxidizing sugar and a neurotransmitter."

The recipe sounds like something from the witches' trio in Macbeth: thou makest beak of squid from strands of sugar and dopamine, once thou oxidizest it in thine cauldron. (Ok, so "dopamine" isn't a very Edwardian word, and don't even start about "oxidizest," let's just move on ...) That sentence is a fairly complete description of the protocol. Everything you need is shown on the left side of part b in this figure from the paper:

A few more details on the ingredients: The strings of sugar are strung-together variants on glucosamine, which you can buy in big jugs at Costco for your joints. I've even seen it advertised at the gas pumps, so it must be a big seller. The cross-linking agent is L-dopa, which is dopamine's cousin molecule. These molecules' cross-linking abilities are mentioned in A World from Dust Chapter 9 -- the same family of molecules that gives you a dopamine rush also defends algae with its cross-linking chemistry. And the important chemical activity is oxidation, which connects to the theme of oxygen and oxidation that runs through A World from Dust.

If you oxidize those two ingredients a little, you get a soft, white sheet. If you oxidize a lot, you get a stiff, brown ribbon, a lot like the Humboldt squid's sharp beak.

Evolution accessed the latent chemical power of sugars, dopamine, and oxidation (outside the cytoplasm, where oxidations are predicted to happen) to make a squid beak. In the lab, we can access that came power to make a stiff, sharp blade without an atom of metal in it. Sounds pretty alchemical to me.
For more, see the original research at Zhang et al., Journal of Materials Chemistry B, "Squid beak inspired water processable chitosan composites with tunable mechanical properties."

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