The meaning of the word biomimicry is being devalued and inflated, to the point that any technology or design with the vaguest resemblance to something in the natural world tends to have the word unthinkingly applied to it. PR people in the automotive and architectural fields are now particularly fond of the word. So it's refreshing to be able to report on some research that has taken a detailed look at a natural phenomenon, the armor of a seahorse, and thought about how it might be applied in the field of robotics. The researchers think a similar structure of sliding plates could be used to improve robot arms used for underwater exploration and bomb disposal.

Though the seahorse isn't the only armored creature on Earth, it is perhaps the most flexible. Its monkey-like prehensile tail allows it to hook onto corals and seaweed. But the researchers wondered whether the armor provides protection from crushing, which is the favored mode of attack used by its natural predators, which include crabs and turtles. By compressing sections of seahorse tails, the researchers found that these could be compressed down to just over half the original width without permanent damage occurring. The tail needed to be compressed by over 60 percent before the spinal column was permanently damaged, with connective tissues and tail muscles absorbing most of the compression. (The seahorses used were already dead.)

The tail of a seahorse comprises 36 segments which get smaller and smaller towards the end of the tail. Each segment is a square-like shape made up of four L-shaped plates, which can both pivot and glide over one another. They are connected to the spinal column by connective tissue. It's this structure that accounts for the great flexibility of the tail.

The structure of a seahorse tail (Image: Joanna McKittrick research group/Jacobs School of Engineering at UC San Diego)

The researchers are using 3D printing to replicate the structure of the plates, which would be attached to polymers to simulate muscles. The intent is to build a robotic arm that synthesizes hard and soft materials (unlike many other robotics projects, which the researchers say tend to favor either one or the other). By creating an arm similar to the tail of a seahorse, researchers think the arm would be able to grasp objects of varying size, rather like a robotic tentacle. How might such an arm be used? Medical devices, exploring the oceans and bomb disposal are all potential uses, the researchers say.

Armor isn't the only interesting thing about seahorses, a genus of fish (Hippocampus) containing 54 known species. They're something of a faunal curiosity shop. "Seahorses are unique in that they have a head like a horse, a long tubular snout like an anteater, a prehensile tail like a monkey, a brood pouch like a kangaroo, camouflage skin like a flounder, and eyes that move independently like a chameleon," said Michael Porter of the Jacobs School of Engineering at UC San Diego where the research took place. "We studied the prehensile tail because [of] its gripping and grasping ability, and it's protected by the natural armor." For their research, the team looked at the common seahorse, Hippocampus kuda.

The team's research appeared in the journal Acta Biomaterialia. You can see a video showing a prototype of the simulated sliding plates in the video below.

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