Researchers at the University of California, San Diego are designing a robotic arm that takes inspiration from the loose, flexible, yet very strong structure of the armored plates on a seahorse's tail. The robot arm will be constructed with polymer muscles that can flex and grasp objects of different shapes and sizes for underwater exploration, detecting and detonating bombs, and as a part of medical devices.
Led by materials science professors Joanna McKittrick and Marc Meyers of the university's Jacobs School of Engineering, the research team described their findings in an article in the journal Acta Biomaterialia (purchase or subscription only).
Seahorses use their prehensile tails to hide from predators by grasping and holding onto seaweed and coral. Although most of the seahorse's predators capture them by crushing them, the animal's prehensile tail can be compressed to about half of its original width before it is completely crushed and damaged beyond repair. The team discovered this by compressing segments from seahorses’ tails at different angles.
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Seahorses get their exceptional flexibility from the structure of their bony plates, which form their armor. Each of the tail's 36 almost-square, ring-like segments consist of four L-shaped plates, which slide past each other. Although most of the seahorse's predators capture them by crushing them, the animal's prehensile tail can be compressed to about half of its original width before it is completely crushed and damaged beyond repair. (Source: Jacobs School of Engineering, University of California, San Diego)
Each of the tail's 36 almost-square, ring-like segments consist of four L-shaped plates, connected by gliding joints that enable the plates to slide past each other. The pivoting joints, which act like mammals' ball-and-socket joints, connect the animal’s vertebrae to each other. The tail plates are attached to the vertebrae by thick layers of extremely flexible collagen.
The researchers conducted chemical tests to determine the highly deformable plate material's properties and structure. They discovered that the material's hardness varies, with plate ridges being 40 percent harder than their grooves, which absorb the energy from impacts. Plate material consists of 40 percent minerals, 33 percent water, and 27 percent organic compounds, primarily proteins.
In the video below, materials science graduate student Michael Porter demonstrates with a model how a seahorse's tail plates are constructed and how they work. Porter is a member of the team and lead author of the article.
"We studied the prehensile tail because of its gripping and grasping ability, and it's protected by the natural armor," he explains in the video. "What's unique about this [structure] is that the bony plates have these sliding mechanisms, where they are able to slide in and out of each other, as all the segments are connected." This structure, and its flexibility, protects the vertebrae from being compressed, as well as giving the tail its ability to twist and bend, and its prehensile ability.
Previously, McKittrick and Meyers had looked at the armor design of several other species, including the scales of different fish, and the armored plates of alligators and armadillos. For the robotic arm project, they were especially interested in finding an animal with armor that was flexible enough for the robot arm. "No one's really looked at the tail and the bones [of a seahorse] in particular as a source of armor," says Porter.
Other robots we've told you about are being built not only with inspiration from nature, but with characteristics that some would say make them androids: living tissue, such as engineered muscles, combined with mechanical and electronic components. For example, the pumping action of cultured rat heart muscle cells propel the silicone muscle structure of the Medusoid robotic jellyfish through water. The Cyberplasm robot goes even further by incorporating engineered cellular devices, electronics, and new methods of communicating between biological and electronic components. Its synthetic muscles, derived from mouse cells, mimic the snake-like movements of the sea lamprey.
Thanks, bob and Greg. When I read about this type of biomimicry in engineering designs, I often imagine engineers working in this area as spending time just looking at various critters and noticing how they're put together, how their subsystems and materials work, and then imagining what can be learned from those observations. From what I've been told, this is how some of these new materials and robot designs are inspired.
Nice article. I continue to be amazed at how living organisms in nature solve the same problem in so many different ways and with so many different techniques. Examples in nature continue to inspire us to think about solving problems using 'new', innovative methods.
Sometimes we get so busy we can't spend an hour or ten just watching mother nature do her stuff. Snorkeling serenely above a coral reef watching the great variety of animals often brings to mind questions and then presents answers. The sharks are there to keep you from becoming too complacent. It's good to read stories like this. Nice work!
I agree, isn't this one fun? I think the materials engineers tend to look not at a particular animal, per se, for inspiration but more at materials and systems of materials, observing them and wondering how they work. In this case, the lead investigators had already checked out fish, alligators and armadillos. The latter two certainly seem like obvious candidates for flexible armor.
It truly amazes me sometimes where researchers are finding inspiration for robots these days. I would never think of a seahorse, as it's a somewhat obscure creature to begin with, as inspiring robotic design. But it makes great sense as presented in your article and the video, Ann. Thanks for staying on top of all these creature-inspired designs. I wonder what they will think of next!
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