To humans the mantis shrimp is known as the “thumb splitter,” due to its propensity to punch the digits out of unfortunate fishers. To its prey on the seafloor, the mantis shrimp is known as “death incarnate”—the crustacean cocks back its two hammer-like appendages under its face, releasing them with such force that they obliterate clam shells, one of the toughest materials in nature. the Mohammed Ali or Tyson Fury of the ocean. One blow and its a knockout. The mantis shrimp has even more fun with crabs, strategically blowing off their claws first so the prey can’t defend itself.
All that bashing puts serious stress on the hammers themselves. So to deal with the constant punching, evolution gave the material of these weapons a “Bouligand” shape. Instead of the layers of material neatly stacking one on top of another, the layers are twisted, almost like the helical structure of DNA. So when a mantis shrimp’s hammer smashes into a thumb or a clam or a crab’s face, any crack in its structure will propagate in a twist pattern, dissipating the energy throughout the material. As a result, the hammer doesn’t snap in half.
Engineers at the University of Southern California and the University of California, Irvine, have invented a clever kind of material based on the mantis shrimp’s clobber-sticks. (If you’re one for formal terminology, they’re called dactyls.) It’s a twist within a twist: They’ve been able to get minerals to grow within a 3D-printed shrimp-inspired Bouligand structure with the help of bacteria, of all things.
The researchers began by 3D-printing a simple lattice structure, basically a grid, out of a polymer. As you can see in the image above, the resulting scaffold had plenty of empty space within—think of it as being like the beams that support a building. They then dipped the whole structure in a bacterial solution and let it sit for 12 to 24 hours. The Sporosarcina pasteurii bacteria in the solution attached to the polymer lattice and started secreting an enzyme called urease.
When the researchers dipped the structure into a second bath of urea and calcium ions, the urease kicked off a chemical reaction that created calcium carbonate. This is the same material that gives a clam’s shell—as well as your own bones and teeth—their strength. It’s also a component of the mantis shrimp’s hammer. In the lab, as the researchers left the scaffolding in the solution, the calcium carbonate kept on accumulating, filling in the lattice entirely within 10 days, and giving the researchers a super-tough material made of a polymer skeleton and mineral innards. The researchers were able to 3Dprint lattices with a variety of interior shapes, from wave patterns to crosses.
Just as the mantis shrimp’s hammer absorbs the energy of its punches without snapping, so too might materials developed with this new method such as body armor, which needs to dissipate a bullet’s energy. Calcium carbonate is also fairly lightweight, so scientists might also be able to grow tougher panels for aircraft or even skins for robots.
In traditional manufacturing, defects can sneak in. Nature, on the other hand, has, over the course of millions of years, developed the wondrous Bouligand structure in the mantis shrimp’s hammer, and it’s a pattern that can be replicated with a simple lattice and a bacterial bath.
Another thing that makes this bacteria-built material special is its ability to regenerate. Like, what if instead of building roads, we grew them? If we have damage, you just introduce bacteria inside, and it can grow it back.
The researchers aren’t there quite yet—they got the bacteria to grow minerals in controlled conditions in the lab, and even then it was only in small quantities. Scaling up for constructing roads would bring additional engineering challenges. So perhaps one day the punching of the mantis shrimp could help fix infrastructure.
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