Sporting horse-like faces, snake-like tails and fish-like gills, seahorses are a hodgepodge of features that seem borrowed from other animals. But the bony plates that give seahorse tails their square shape are an anomaly in nature — and that's precisely what caught the attention of researchers interested in improving robots.
Since that square tail structure is so unusual in nature, scientists were curious about the advantages it might have over the more cylindrical shape seen in the tails of most other animals. They performed tests to compare the two, and the results, which they reported in the journal Science, show that this shape affords flexibility without compromising strength.
"We found that this square architecture provides adequate dexterity and a tough resistance to predators, but also that it tends to snap naturally back into place once it's been twisted and deformed," said study co-author Ross Hatton of the College of Engineering at Oregon State University in a statement. "This could be very useful for robotics applications that need to be strong, but also energy efficient and able to bend and twist in tight spaces."
Among those applications are search-and-rescue missions and even laparoscopic surgery — which entails using a robotic device to probe around inside a patient's body so surgeries can be performed using smaller incisions. Modeling laparoscopes after a seahorse tail could improve the ability to maneuver around organs and bones while maintaining the strength necessary to perform surgical tasks.
Using a combination of 3D-printed models and computer models such as the one shown above, the researchers compared the seahorse's square-shaped tail with more standard cylindrical tails. When a cylindrical tail gets crushed, it's pretty much game over. But when a seahorse's squarish tail gets crushed, they found, those square bony plates can act as a shock absorber.
The plates slide past each under when put under pressure, which can help prevent the spine from fracturing. And even more remarkably, they can snap back into their original position without using much additional energy.
This ability is useful for a seahorse because it uses the tail to anchor its body to coral or seaweed while snatching whatever food floats by. The arrangement of bony plates needs to be strong enough to allow the seahorse to hang on despite the current – and to help protect it from getting eaten by predators – but flexible enough that the seahorse can move around to grab food.
"Human engineers tend to build things that are stiff so they can be controlled easily," said study co-author Ross Hatton, also of Oregon State University, in a statement. "But nature makes things just strong enough not to break, and then flexible enough to do a wide range of tasks. That's why we can learn a lot from animals that will inspire the next generations of robotics."