Flexible Armor: Mysterious Seahorse Astounds Scientists

Seahorse Armor Inspire Robotic DesignsPlayJacobs School of Engineering, UC San Diego
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The curious seahorse, a tiny fish that swims in a vertical position and looks a lot like a miniature horse, has astounded researchers by its ability to withstand crushing forces that would destroy nearly every other living creature.

And it just may help the researchers borrow from the world of biology to solve some really tough problems in the world of engineering.

The seahorse is the latest in a growing list of organisms in the relatively new field of biomimetics. If you are trying to solve an engineering problem, find something in nature that has already done it, then steal its secrets.

Engineers at the Jacobs School of Engineering at the University of California, San Diego, have been studying several animals to see how they protect themselves.

Their goal is to develop a device that can grab an object, even something deep under the sea, while withstanding the forces of nature and the threats from predators.

A monkey's tail would work, because a monkey can curl its tail around a branch and hang from a tree. In technical jingo, that tail is a "flexible prehensile" extension.

PHOTOS: Seahorse Armor Inspires Robotic Designs

The engineers looked at all sorts of critters, including a large fish that survives in the piranha-infested waters of Brazil's Amazon forest, and is protected by a layer of armor that is more than a match for the razor-sharp teeth of the piranha.

But you can't pick up something with the body of a fish, so they turned elsewhere.

"We started out looking at antlers, and horns, as defense, then we went on to the armadillo and turtle shells, as armor," materials science professor Joanna McKittrick of UCSD said in a telephone interview. But what they needed was a truly remarkable creature, and the seahorse stepped up to the plate.

"The seahorse was a natural," Mckittrick said. The research, led by McKittrick and fellow materials science professor Marc A. Meyers, was published in the journal Acta Biomaterialia, and it describes seahorses like this:

"They have a head like a horse, a long tubular snout like an anteater, eyes that move independently like a chameleon, a brood pouch like a kangaroo, camouflage skin like a flounder, and a flexible prehensile tail like that of a monkey."

That sounds like an animal designed by a committee that wasn't entirely sure what it wanted to do. But as the researchers subjected dead seahorses to forces powerful enough to compress their body to half their normal size, they found something extraordinary. That amount of compression, which would kill just about anything else, except a sponge, did no discernible damage to the seahorse.

McKittrick said that when she saw the fish's ability to withstand that, she was "bamboozled." That's an engineering term for stunned, or astonished, or really surprised.

The researchers found that the seahorse's vertebra, which runs the length of its body, is protected by a series of "bony plates" that slide past each other during compression.

But Michael Porter, a doctoral student who conducted most of the lab work and is lead author of the study, said in a telephone interview that the finding was surprising because bone would be expected to crack, and then shatter under such compression. That's because bones are made mostly from minerals and are brittle.

Minerals comprise 65 percent of a cow bone, for example, and that bone would shatter under severe compression.

But the seahorse's bony plates are only about 40 percent mineral. The rest is organic compounds and water, so the plates eventually deform at compression beyond 50 percent, but they don't break.

"We had expected the bony plates to break," Porter said. "But most of the load (from compression) was transferred to the tissue that connects the overlapping plates as they slide past each other."

So presumably, a live seahorse that is caught in the jaws of crab should be able to go on with its life if it is compressed no more than 50 percent. It will likely find a piece of coral and wrap its remarkable tail around it and hang around for another day.

And that's pretty much what the engineers would like to reproduce.

They want to build a "gripping device" that can operate in hostile environments, like the ocean, while protecting itself from predators with some kind of armor that can withstand incredible forces.

Such a device could be useful in applications ranging from unmanned bomb detonation to -- if they can make it small enough -- medical tools that could work inside the human body.

"We think we can assemble something that's based on the seahorse," McKittrick said. "At least that's what we're trying to do. We haven't done it yet."

Incidentally, the researchers didn't have to kill the seahorses for their experiments. The animals were on their way from Bali, Indonesia, to join the aquarium at nearby Scripps Institute of Oceanography when they "died, due to stress, during transport," the study notes.

Of course, scientists and engineers have tried to borrow from nature for centuries. The Wright brothers, in their quest to build a flying machine, studied pigeons. Fortunately, they were smart enough to figure out that flapping wings is probably not the way to go.

Today, however, researchers around the world are trying to mimic biological systems, and they have turned to some of nature's most ingenious designs.

Scientists at Helsinki University, Finland, unraveled the mystery of how a water spider can walk on water. They produced a material that is so buoyant that a boat made from one pound of the stuff could carry 1,000 pounds. That's about five kitchen refrigerators.

The spider's secret -- its superlight construction -- led to aerogels, made from plant cellulose and air, that are so light the researchers described them as "solid smoke."

Scientists at Britain's West Chester University turned to whales and dolphins to improve the design of turbines. That work was led by a guy with an appropriate name: Frank Fish. Honest.

Ohio State University scientists are caught up in cockroaches these days.

This "biological and engineering marvel," as they described it, can run fast, turn abruptly, and react to an obstruction in its path faster than a nerve impulse can travel. Ideal model for all terrain vehicles in space, and on earth.

Others are looking at caterpillars for soft robots, bats for better radar, squid for camouflaging, and on and on.

It appears that nature, indeed, is still the best engineer on the planet.