A seahorse's skeleton, as well as the bony plates, shown though a micro CT-scan of the animal (CREDIT:�McKittrick Research Group)

Seahorse's armour aids robotic arm design

Engineers have turned to the seahorse’s tail for inspiration in making robust robotic arms.

The tail of a seahorse is exceptionally flexible and can be compressed to about half its size before permanent damage occurs due to its structure of armoured plates that slide past each other, engineers at the University of California, San Diego, have found.

Researchers are hoping lessons learned from the animals can be used to create a flexible robotic arm equipped with muscles made out of polymer, which could be used in medical devices, underwater exploration and unmanned bomb detection and detonation.

"The study of natural materials can lead to the creation of new and unique materials and structures inspired by nature that are stronger, tougher, lighter and more flexible," says McKittrick, a professor of materials science at the Jacobs School of Engineering at UC San Diego, who led the study alongside fellow professor Marc Meyers.

McKittrick and Meyers had sought inspiration by examining the armour of many other animals, including armadillo, alligators and the scales of various fish, but this time they were specifically looking for an animal that was flexible enough to develop a design for a robotic arm.

"The tail is the seahorse's lifeline," says Michael Porter, a Ph.D. student in materials science at the Jacobs School. "But no one has looked at the seahorse's tail and bones as a source of armour."

The tail’s primary purpose is to allow the animal to anchor itself to corals or seaweed and hide from predators.

But as most of the seahorse's predators, including sea turtles, crabs and birds, capture the animals by crushing them the engineers wanted to see if the plates in the tail act as an armour.

Researchers took segments from seahorses' tails and compressed them from different angles, finding that the tail could be compressed by nearly 50 per cent of its original width before permanent damage occurred.

This is because the connective tissue between the tail's bony plates and the tail muscles bore most of the load from the displacement and even when the tail was compressed by as much as 60 per cent, the seahorse's spinal column was protected from permanent damage.

The seahorse's tail is typically made up of 36 square-like segments, each composed of four L-shaped corner plates that progressively decrease in size along the length of the tail, which are free to glide or pivot.

Gliding joints allow the bony plates to glide past one another while pivoting joints are similar to a ball-and-socket joint, with three degrees of rotational freedom.

The plates are connected to the vertebrae by thick collagen layers of connective tissue and the joints between plates and vertebrae are extremely flexible with nearly six degrees of freedom.

"Everything in biology comes down to structures," Porter says.

The next step for the group, who detail their findings in the March 2013 issue of the journal Acta Biomaterialia, is to use 3D printing to create artificial bony plates, which would then be equipped with polymers that would act as muscles.

The final goal is to build a robotic arm that would be a unique hybrid between hard and soft robotic devices, which would be both flexible and robust and could be used for medical devices, underwater exploration and unmanned bomb detection and detonation.

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