Seahorses don’t exactly radiate toughness, but recent studies show that the bone structure of these delicate fish might be the key to unlocking a breakthrough in robotic armor. Iron Man á la seahorse?
First of all, yes, seahorses are in fact fish. Their genus name, “Hippocampus,” stems from the ancient Greek hippos meaning “horse,” and kampo meaning “sea monster.”
These tiny “sea monsters” (the largest reaching eight inches in length) face a multitude of challenges in open water, the most problematic being that they are poor swimmers. The fifty-four known species of seahorses must spend their days clinging to kelp, sea-grass, and coral so as not to be carried away by strong currents while feeding on crustaceans—something they must do constantly as their digestive tracts are extremely short.
What do the engineers at University of California San Diego (UCSD) Jacobs School of Engineering want with a teensy-tiny poor-swimming eating machine? The treasure is in the tail.
Seahorses use their prehensile (grasping) tails as anchors, holding them in place while they feed. The tails have to be strong enough to protect them, but flexible enough to wrap around rocks and move with the tide.
“The tail is the seahorse’s lifeline,” Michael Porter, a Ph.D. student in materials science said in an interview.
The typical tail is made up of thirty-six bony segments. Because most of their predators (including crabs, rays, turtles, and seabirds) capture seahorses by crushing them, the Jacobs team wanted to see if the bone segments act as protective armor.
In order to study the bones’ structure more clearly, the team used a chemical process to strip them of their minerals and proteins. Amazingly, seahorse tail-bones contain a lower-than-most percentage of hard minerals (15 percent lower than cow bone). When we think of shielding materials, we often assume the stronger the better. But just like foam or other porous materials, the tail bones actually absorb energy during impact.
“The connective tissue between the tail’s bony plates and the tail muscles bore most of the load from the displacement,” the team said.
Each segment of the tail is composed of four L-shaped corner plates which are connected by small joints that allow the bone plates to glide and pivot freely over one another without being damaged. The structure is reminiscent of the Hoberman Sphere toys we all know and love.
“[In our tests] the tail could be compressed by nearly 50 percent of its original width before permanent damage occurred…even when the tail was compressed by as much as 60 percent the seahorse’s spinal column was protected from permanent damage,” the team found.
If the team is successful in recreating this structure, imagine the applications of armored plating that could withstand that kind of pressure.
The Jacobs team plans to use 3D printers to create artificial bony plates lined with polymer muscles, which will help them to better understand how to apply these structures to their robotics.
“The final goal is to build a robotic arm that would be a unique hybrid between hard and soft robotic devices. A flexible, yet robust robotic gripper could be used for medical devices, underwater exploration and unmanned bomb detection and detonation,” they said.
Image by Jacobs School of Engineering.