A double helix
Scientists know that the tusk constantly twists within the left-handed course and that it’s composed of dentine lined by a skinny layer of cementum encasing a central pulp chamber. The dentine and cementum, in flip, are made up of microscopic collagen fibrils mineralized with nanoparticles of hydroxyapatite. The macroscale spiral form emerges one way or the other from how these fibrils arrange themselves. That construction additionally determines the tusk’s materials properties. One query is whether or not the helical construction can be current on the micro- and nanoscale.
However no one had mapped the inside construction in three dimensions on the atomic, nano, and macroscales. So the authors of this newest paper studied two male narwhal tusk and cranium specimens by combining a number of imaging strategies: X-ray computed tomography, scanning X-ray diffraction, scanning small-angle X-ray scattering and tensor tomography, and bifringence microscopy. That required reserving time on three giant synchrotrons in Sweden, Switzerland, and France. In addition they carried out normal morphological measurements and performed mechanical three-point bending assessments.
The outcomes confirmed that the collagen fibrils and hydroxyapatite nanoparticles orient themselves alongside the tusk’s longitudinal axis, so there’s a constantly excessive diploma of anisotropy in any respect scales. However there are tiny systemic deviations at small angles in that orientation, which in flip create the twisted construction. Whereas the cementum layer types the identified left-handed helix, the dentine types a right-handed helix.
That double-helix construction is the key to the tusk’s outstanding stiffness and energy, with the versatile fibers and stiff mineral matrix enabling the tusk to face up to robust forces, like bending and twisting with out cracking. It additionally permits the narwhal tusk to develop straight, in contrast to, say, an elephant’s curved tusk. The crew additionally famous a finer underlying microstructure within the cementum of collagen fiber bundles radially extending outward, which they plan to review additional utilizing micro- and nano-beam experiments.
“Since whales can reside for as much as 80 years, their enamel kind a form of historic file of fixing environmental circumstances all through the animal’s lifetime,” said co-author Henrik Birkedal of Aarhus College in Denmark. “And since the North Atlantic is at present present process very fast adjustments, it’s apparent to research whether or not we will hint these adjustments within the laborious tissue of the narwhal tusk. That’s what we are actually engaged on.”
DOI: Nature Communications, 2026. 10.1038/s41467-026-75689-z (About DOIs).
