How do sharks and rays maintain a seamless, protective skeletal covering as they grow? This question has intrigued scientists for years, particularly Professor Mason Dean, a marine biologist at City University of Hong Kong (CityUHK).
Professor Dean, an expert in vertebrate skeletal development, has long been fascinated by how nature efficiently manages complex surfaces during growth. The challenge of keeping a protective layer intact while the underlying structure expands is not just a biological puzzle but also a topic of interest for mathematicians, architects, and engineers exploring 3D printing and material science.
The Unique Skeletal Armor of Sharks and Rays
Unlike most fish, sharks and rays possess skeletons made entirely of cartilage—a flexible yet sturdy material similar to human knee cartilage. However, what sets them apart is their distinctive armored layer composed of thousands of tiny, interlocking tiles called “tesserae.” These minuscule skeletal components create a tough yet flexible structure that evolves as the animal grows.
So how does this remarkable system adapt to accommodate the increasing size of the animal? Do existing tesserae enlarge, or are new ones added? Professor Dean and his research team in Germany sought to unravel this mystery in their latest study, published in Advanced Science.
Advanced Imaging Unlocks the Secret of Growth
To analyze how tesserae adapt over time, the researchers utilized high-resolution micro-CT scans to map their distribution across different life stages of stingrays. Their findings revealed a fascinating biological phenomenon:
- As stingrays grow, their skeletons expand without altering their overall shape—this process is known as isometric growth.
- Instead of forming new tesserae, the existing ones grow larger, ensuring the skeletal armor remains intact.
The Mathematical Perfection of Tesserae Growth
One of the most intriguing aspects of this research is how tesserae maintain a near-perfect geometric pattern. The dominant shape remains hexagonal, with a balanced mix of pentagons and heptagons—similar to the pattern seen on a soccer ball but with greater complexity.
However, a critical question arises: how does nature regulate this precise arrangement? The intuitive assumption would be that all tesserae grow at the same rate, but simulations proved that this approach would lead to gaps in the armor, causing structural breakdown.
Instead, the researchers discovered a remarkable natural adaptation: larger tesserae grow at a faster rate. This proportional growth ensures that gaps emerging during expansion are automatically filled, eliminating the need for additional tiles while maintaining a continuous protective layer.
How Stingray Skeletons ‘Sense’ Growth Needs
The study suggests that specialized cells between the tesserae may play a crucial role in this process. These cells appear to detect strain differences in the growing skeleton, signaling the appropriate rate of expansion for each tessera. This self-regulating system ensures seamless armor growth from birth to adulthood.
Nature’s Blueprint for Innovation
Stingrays have been using this geometric armor solution for hundreds of millions of years, offering valuable insights into nature’s ability to overcome structural challenges. Professor Dean believes that understanding these biological principles can revolutionize materials science, inspiring innovations in biomimetic design, adaptive architecture, and advanced manufacturing techniques.
By mimicking nature’s elegant solutions, researchers and engineers can develop more efficient, flexible, and durable materials for real-world applications.
Reference:
Binru Yang et al, Growth of a Tessellation: Geometric Rules for the Development of Stingray Skeletal Patterns, Advanced Science (2024). DOI: 10.1002/advs.202407641