The Atlantic wolffish possesses teeth that are incredibly robust, capable of crushing prey with hard shells, and recent studies have discovered that these teeth contain an exceptionally rare material that aids in this function.
An international group spearheaded by scientists from Hebrew University in Jerusalem, Israel, has determined that the osteodentin within the teeth of the Atlantic wolffish is auxetic, contracting in all directions when pressed along its length.
This finding provides insight into how the teeth of the wolffish can endure repeated and extreme forces. It may also contribute to the creation of innovative, stronger, and more durable synthetic materials.
In contrast to most materials, which tend to expand laterally when compressed lengthwise, the researchers observed that when they exerted force along the axis of the tooth mirroring the wolffish’s natural biting strength, the osteodentin consistently contracted both laterally and longitudinally. This phenomenon is characteristic of materials exhibiting a negative Poisson’s ratio, signifying materials that widen when pulled and narrow when compressed, contrary to typical materials.
For each of the eight teeth studied, the researchers predominantly recorded Poisson’s ratio values for the osteodentin in the range of -1 to -2, a value range seldom encountered in manufactured materials. For instance, most steels are around 0.3, while rubber approximates 0.5.
The atypical auxetic characteristics of the osteodentin are believed to relate to the teeth’s microstructure. Canals measuring 10–20μm in diameter extend from the base to the tip of a wolffish tooth, curving outward as they ascend. When pressure is applied to the tooth, these canals collapse inward, reducing the osteodentin laterally and enhancing the tooth’s strength.
There are several natural instances of auxetic behavior, including the achilles tendon, cat skin, and zeolites. More than a decade ago, researchers in France engineered a material that expanded in volume whether it was stretched or compressed. Its structure consisted of a single wire twisted into a helix, entangled into a disordered mass, and then compacted into a cylinder. In 2016, US researchers also created a protein crystal sheet that thickened when stretched and contracted when compressed.