The narwhal is sometimes called the unicorn of the sea and is recognised by its mythical spiral “horn”, which is in fact a tooth that grows out from the jaw. The tooth has raised many questions, but researchers, including those from Chalmers University of Technology, have now been able to uncover one of its secrets. Using state-of-the-art X-ray techniques, they have for the first time managed to show exactly how the spiral tooth is structured, knowledge that could inspire new materials. The next step is to investigate whether the tooth can provide clues about how the climate has developed in the Arctic region where the narwhal lives.
In the Middle Ages, there was a belief that the narwhal’s tooth was a unicorn horn, in possession of magical powers. To achieve prestige and influence, the Danish king Frederick III had the kingdom’s coronation throne crafted from narwhal tusks. The throne remained in use until the mid-19th century and can today be seen at Rosenborg Castle in Copenhagen.
Using X-ray techniques to investigate the tooth
Today we know that the narwhal’s tooth does not have magical powers, but it has been something of a mystery until now. In a new study, published in the scientific journal Nature Communications, the narwhal’s tooth has been mapped using state-of-the-art X-ray techniques at three synchrotron facilities: the MAX IV Laboratory in Sweden, the Swiss Light Source at the Paul Scherrer Institute in Switzerland, and the European Synchrotron Radiation Facility in France. The study is part of the research project ”Narwhal tusks – a tale with a twist” and has been carried out by researchers from Aarhus University, the Paul Scherrer Institute, Chalmers University of Technology, and the Greenland Institute of Natural Resources.
Through a broad collaboration involving chemistry, physics, materials science and biology, the researchers mapped the tooth in three dimensions: at the atomic, nano and micro scales. The researchers combined different X-ray methods, including tensor tomography, a powerful type of 3D X-ray imaging.
A double spiral provides exceptional stability
The study shows that the tooth does not consist of one spiral, but two. Nature has constructed it like a twisted rope, where the outer layer forms a spiral that twists to the left, while the mineralised collagen structures inside the tooth follow a spiral in the opposite direction. This double spiral gives the tooth exceptional stability, enabling it to withstand significant stress.
“What surprised me the most was that we found that the mineralised collagen, the building blocks, already formed a spiral in a millimeter-sized sample piece even though the tusk is meters long,” says Marianne Liebi, Assistant Professor at EPFL, Group Leader at the Paul Scherrer Institute, and Affiliate Docent at Chalmers University of Technology.
“The project really became interdisciplinary. We really needed the collaboration of all project partners to understand the overall structure in the bigger picture. It could not have been possible without physicists, chemists, marine biologists, and material scientists," says Adrian Rodriguez Palomo, who was a PhD student at Chalmers University of Technology, Sweden, when he joined the project, and continued the study as a postdoctoral researcher at the Department of Chemistry at Aarhus University, Denmark.
Could inspire new materials and provide insights into climate change
The way in which nature has constructed the tooth’s advanced material with such extreme properties could, in the long term, inspire new, strong materials.
However, as the narwhal can live for up to 80 years, its tooth – like the growth rings of a tree – could also provide new insights into environmental and climate conditions in the Arctic; a region where the climate is changing rapidly. This is the next step for the researchers to investigate.
Mer om forskningen
The study The narwhal tusk assembles its macroscopic helix from building blocks with opposing twists was published in Nature Communications and is written by Adrian Rodriguez-Palomo (Aarhus University and Chalmers University of Technology), Henrik Birkedal (Aarhus University), Marianne Liebi (Chalmers University of Technology, Paul Scherrer Institute, EPFL), Eva Garde and Mads-Peter Heide Jørgensen (Greenland Institute of Natural Resources).
The study is part of the NordForsk-funded research project ”Narwhal tusks – a tale with a twist” and has also received funding from the Marie Skłodowska-Curie programme within EU Horizon 2020.
For more information, please contact:
Marianne Liebi, Assistant Professor at EPFL and Group Leader at the Center for Photon Science, Paul Scherrer Institute, and Affiliate Docent at the Department of Physics and Astronomy, Chalmers University of Technology, marianne.liebi@psi.ch, +41 79 795 86 93
Adrian Rodriguez Palomo, Interdisciplinary Nanoscience Centre (iNANO), and Department of Chemistry, Aarhus University, Denmark. Adrian Rodriguez Palomo received his PhD in 2022 from Chalmers University of Technology with the thesis Multimodal Imaging of Anisotropic Hierarchical Materials, adrian.rodriguez@esrf.fr, +33 476 88 26 24
The text is partly based on press releases about the study from Aarhus University and the Paul Scherrer Institute.