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Biocomposites: Metal makes ant teeth hard

Biomaterial : Ants bite too metallic teeth

Thanks to an unusual combination of materials, the jaws of some animals are far superior to our teeth. They are just as hard & nbsp; – but much more stable. by Lars Fischer A red wood ant is sitting on one hand and looking at the camera.© Henrik_L/Getty Images/iStock (detail)

Ants have to use 60 percent less force to bite things than animals with normal teeth. As a result, they effortlessly cut leaves or even break open the shells of other insects, even though their jaws are often finer than a human hair. Their trick is a cutting edge that, thanks to embedded metal atoms, can be much sharper than classic biocomposites, reports a working group headed by Robert M. & nbsp; Schofield from the University of Oregon. In contrast to tooth enamel, for example, it does not consist of crystals embedded in a basic mass of proteins, but of a homogeneous material whose proteins are & raquo; hardened & laquo; with metal atoms such as zinc or manganese. are. As the team in & raquo; Nature & laquo; writes, it is as hard as classic biocomposites like those in teeth or crab claws, but more precisely structured and also more break-resistant.

Schofield's team has been investigating biomaterials enriched with heavy elements for some time – a class of substances that is not only common in ants, but also in scorpions, spiders and some marine animals. For a long time it was a mystery how these composite materials are structured. The very high metal content, up to 18 percent in the teeth of marine worms, actually suggests that fine pieces of metal are also embedded in the protein of the jaw. But measurements show that the metal atoms are not connected to one another. Instead, with the help of atom probe tomography, the working group has now shown that the metal is homogeneously distributed even in the finest structures.

Due to their special chemical properties, these metal atoms function as & raquo; cross braces & laquo; which link proteins within and among each other and make the material harder. As a result, the material from which the ants 'teeth or the scorpions' stings are made is of a uniform structure. In classic composite materials, on the other hand, there are hard materials next to soft ones, and the two components absorb loads very differently. For example, the material of teeth can break at the boundary between the hard mineral and the more flexible protein, especially with very fine structures be much thinner & nbsp; – and therefore much sharper. The leaf cutter ant Atta cephalotes is only 50 nanometers thick. At the same time, the chemical crosslinking through the metal atoms has another effect. The metal forms coordinative bonds with the proteins – and these can be loosened and re-established. As a result, these metal-containing biomaterials are extremely abrasion-resistant, as Schofield's team found in mechanical tests. If cracks develop in the material, it can heal itself because the metal atoms simply re-establish loose bonds.

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