February 11, 2014
Ants Depend On A Tiny Neck Joint To Do Heavy Lifting: Study
[ Watch the Video: Neck Joint The Key To An Ant's Strength ]
April Flowers for redOrbit.com - Your Universe Online
The findings show that the neck joint of a common American field ant can withstand pressures up to 5,000 times the ant's weight.
“Ants are impressive mechanical systems—astounding, really,” said Carlos Castro, assistant professor of mechanical and aerospace engineering at The Ohio State University. “Before we started, we made a somewhat conservative estimate that they might withstand 1,000 times their weight, and it turned out to be much more.”
The engineering team is studying whether similar joints could help robots in the future to mimic the ant's weight-lifting ability on Earth and in space.
Ants have been observed in the field for a long time, with researchers guessing that the insects could hoist more than one hundred times their weight, judging by the payload of leaves or prey they carried.
Castro's team decided to take a different approach by taking the ants apart.
“As you would in any engineering system, if you want to understand how something works, you take it apart,” he said. “That may sound kind of cruel in this case, but we did anesthetize them first."
The team reverse engineered the Allegheny mound ant as if it were a device, by testing its moving parts and the materials it is made of. The Allegheny mound ant -- a common ant not particularly known for its lifting ability -- was chosen because it is common in the Eastern US and could easily be obtained from the university insectary.
First, the scientists imaged the ants using electron microscopy and x-rayed them with micro-computed tomography (micro-CT) machines. The ants were then placed in a refrigerator to anesthetize them and glued face-down to a specially designed centrifuge. This measured the force necessary to deform the neck and eventually rupture the head from the body.
The centrifuge works on the same principle as a carnival ride called "the rotor," which uses centrifugal force to pin people to the walls as the floor drops away. In the experiment, the ants' heads were glued down, so the centrifugal force pulled outward until their necks ruptured.
As the centrifuge spun up to hundreds of rotations per second, more outward force was exerted on the ants' bodies. The neck joint began to stretch and the body lengthened at forces corresponding to 350 times the ants' body weight, but the necks didn't rupture until the centrifuge reached forces 3,400 – 5,000 times their average body weight.
The soft tissue structure of the neck and its connection to the hard exoskeleton of the head and body was revealed by micro-ct scans. The team used electron microscopy to discover that each part of the head-neck-chest joint was covered in a different texture, with structures that looked like bumps or hairs extending from different locations.
“Other insects have similar micro-scale structures, and we think that they might play some kind of mechanical role,” Castro said. “They might regulate the way that the soft tissue and hard exoskeleton come together, to minimize stress and optimize mechanical function. They might create friction, or brace one moving part against the other.”
The interface between the soft material of the neck and the hard material of the head is another key feature of the body's design. Such transitions normally create large stress concentrations. The ants' bodies, however, have a graded and gradual transition between materials, which gives an enhanced performance. This is a design feature that could prove useful in man-made designs.
“Now that we understand the limits of what this particular ant can withstand and how it behaves mechanically when it’s carrying a load, we want to understand how it moves. How does it hold its head? What changes when the ant carries loads in different directions?”
The team hopes that their research could one day lead to micro-sized robots that will combine hard and soft sections, much like the ants' body does. Much of the current work in robotics involves assembling small, autonomous devices that can work together.
If researchers try to create large robots based on the same design, Castro explained, a difficult problem will emerge.
The incredible strength of an ant is based on the fact that their bodies are so light inside their hard exoskeletons, so their muscles don't have to provide much support. This leaves the tiny ant free to apply all their strength to lifting other objects.
Humans, in contrast, can carry comparatively heavy loads due to our body weight. Supporting that weight, our muscles don't have much strength left over to lift other objects.
An ant, on a human-sized scale, are overcome by basic physics. As their overall volume increases (dimensions cubed), their weight also increases. However, the strength of their muscles only increases with surface area (dimensions squared). So, should a human-sized ant actually exist outside your favorite grade B horror movie, it would be unsuccessful in carrying extreme loads at a human-scale.
In microgravity, however, a large robot based on the ants' body design might be able to carry and tow cargo. It might be possible, someday, that we use giant robot ants in space.
The researchers will continue their study with the ants’ muscles, perhaps using magnetic resonance imaging and computer simulations to answer the questions of how to scale up similar structures.
This study was begun by Blaine Lilly, associate professor of mechanical and aerospace engineering, and his former student Vienny Nguyen. Based on this project, Nguyen earned her Master's degree and is now working as a robotics engineer at NASA's Johnson Space Center. Castro and Lilly have also begun a collaboration with Noriko Katsube, also a professor of mechanical and aerospace engineering, and an expert in mechanical modeling of biomaterials, and graduate student Hiromi Tsuda.