Hairworms are found all over the world in seawater, they have inhabited the oceans for hundreds of millions of years. Nevertheless, some of their peculiarities have only been deciphered now: their jaws are made of a remarkably stable material, and the secret of this stability can now be explained by experiments at TU Wien in cooperation with Max Perutz Labs.
The metal atoms, which are incorporated into the protein structure of the material, play a decisive role. They make the material hard and flexible at the same time, very similar to ordinary metals. Further research on this class of materials aims to produce new materials that can be used industrially in a natural way.
Individual metal atoms
“The materials from which vertebrates are made are well studied,” explains Professor Christian Hellmich from the Institute for Structural and Materials Mechanics at TU Wien. “Bones, for example, are very hierarchical: there are organic and mineral parts, tiny structures are combined to form larger structures, which in turn form even larger structures.”
It’s different with furry worms. Their jaws are extremely strong and unbreakable, but they do not contain mineral granules like vertebrate bones do. Instead, they contain metals. Of course, this has nothing to do with pure metal objects such as gold teeth or artificial titanium hips: the hairworm uses metals such as magnesium or zinc as individual atoms which are incorporated into a protein structure.
“On its own, the fact that there are metal atoms in the jawbone of the hairworm does not explain its excellent material properties,” explains Christian Hellmich. The typical properties known to everyday metals – apart from their hardness and elasticity, especially their toughness – are ultimately only created by the interaction of many atoms. Sliding surfaces are created along which atoms move against each other. This can be studied with so-called nanoindentation tests: A force is exerted on the material in a precisely defined way, then the resulting deformations are studied. Surprisingly, it turned out that the material of the hairworm jaw behaves very similarly to metal.
An old and efficient material
“The construction principle that made the hairworm jaws so successful apparently originated around 500 million years ago,” says Florian Raible of Max Perutz Labs, a joint venture between the University of Vienna and the Vienna Medical University. “The metal ions are incorporated directly into the protein chains and then ensure that different protein chains are held together.” In this way, the hairworm can produce three-dimensional shapes from a particularly stable protein matrix.
At the same time, this structure also allows deformation: when an external force is exerted on the material, the protein chains can slide over each other. The material allows for elastoplastic deformations, rather than being brittle and brittle.
“It is precisely this combination of high strength and deformability that is normally characteristic of metals,” says Luis Zelaya-Lainez, lead author of the study, who used materials science techniques to examine the tiny jaws. “Here we are dealing with a completely different material, but it is interesting that the atoms of metal still provide strength and deformability in it, just like in a piece of metal.”
While industrially made metals can only be produced using a large amount of energy, the hairworm achieves a similar feat in a much more efficient manner. “Biology could serve as inspiration here, for completely new types of materials,” Hellmich hopes. “Maybe it’s even possible to produce high performance materials in an organic way – much more efficient and environmentally friendly than what we manage today.”
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