May 2, 2013
Designing Flexible Robots Based On Seahorse Tail Armor
WATCH VIDEO: [Seahorse Armor Offers Insight Into Robotic Design]
Alan McStravick for redOrbit.com - Your Universe Online
In November of last year, redOrbit reported on a study out of the Ohio State University (OSU) looking into the material characteristics of butterfly wings and rice leaves in the hopes of improving products that might facilitate the flow of fluids.
The seahorse, with a flexible tail comprised of bony, armored plates capable of sliding past one another, is able to compress its appendage to just over half of its original size before permanent damage occurs. This structure is inspiring researchers to create a similarly-styled structure for use in a robotic arm with more flexibility. The team believes this type of arm would find use in the medical field as well as the fields of underwater exploration and unmanned bomb detection and detonation.
A previous study by the team focused on the armor of several other animals. Among previous study subjects were armadillos, alligators and abelones, as well as the scales of various fish. However, they knew to look to the seahorse for the inspiration needed for the development of a robotic arm.
According to Michael Porter, a PhD student and colleague on the study, “The tail is the seahorse´s lifeline.” He says this in reference to their ability to utilize their tail as a means to anchor itself to corals or seaweed and to be able to hide from predators. He continues, “But no one has looked at the seahorse´s tail and bones as a source of armor.”
Animals that prey upon the seahorse, including sea turtles, crabs and birds, typically capture them by crushing them. The material science engineers were interested in learning if the plates in the tail acted as a form of armor. To do this, they took segments from seahorses´ tails and compressed them from different angles. In this undertaking, they learned the tail could be compressed by nearly 50 percent of its original width before any permanent damage would occur. The reasoning for this lies in the fact that the connective tissue between the tail´s bony plates and tail muscles absorbed the bulk of the pressure resulting from the displacement. Additionally, it was learned continuing the compression to as much as 60 percent still protected the seahorse´s spinal cord from permanent damage.
To understand the structure and property of a subject material, the team employed the use of a chemical technique that is able to strip either the protein or mineral components away. The treatment of the bony plates of the seahorse´s tail showed a relatively low percentage of mineral as a base component — around 40 percent. By comparison, the cow bone has a mineral percentage closer to 65 percent. Additionally, the seahorse plate contains 27 percent organic compounds, consisting primarily of proteins. The remaining 33 percent is water.
Different regions of the plate varied in their degrees of hardness. The ridge presented the hardest surface. This, it is assumed, is for impact protection. The plate´s grooves were, due to their more porous nature, significantly softer than the ridge. The researchers theorize this region is responsible for energy absorption from impacts.
The 36 square-like segments that make up a seahorse tail progressively decrease in size along the length of the tail. Each plate, composed of four L-shaped corner plates, have the ability to either glide or pivot. The pivoting joints are similar to our own ball-and-socket joints and allow for three degrees of rotational freedom. Each plate is connected to the vertebrae by thick collagen layers of connective tissue.
“Everything in biology comes down to structures,” Porter said in a statement.
The team sees the burgeoning technology of 3D printing as being the next avenue to creating artificial bony plates. These new plates would then be equipped with polymers that would act as muscles. Ultimately, this new structure would be used in the creation of a hybrid robotic arm, unique for the combination of both hard and soft robotic devices. The prospective fields for such a robotic arm, mentioned above, would benefit from the protected, flexible arm being able to grasp a variety of objects of different shapes and sizes.