By Matthew Stock
A robotic salamander that can replicate the amphibian's movement to an unprecedented degree of accuracy has been built by robotic engineers in Switzerland. Called Pleurobot, it can reproduce the many postures and positions of a real salamander, and can even swim underwater. Researchers hope it will give neuroscientists an important new tool for further understanding the way the nervous system co-ordinates movement in vertebrates.
Pleurobot was developed at the Biorobotics Laboratory at the Swiss Federal Institute of Technology in Lausanne (EPFL), who have previously built other bio-inspired robots. Professor Auke Ijspeert led the development and explained why the salamander is such an important creature for scientists to study.
"It's a key animal from an evolutionary point of view," he said. "It's older than crocodiles and dinosaurs; it's an amphibian. So if you look at the modern salamander, its morphology and body shape is very close to the fossils of the first terrestrial vertebrates. So by studying the modern salamander we have a time window to the ancestors of all terrestrial vertebrates, including humans."
Ijspeert added that Pleurobot has proved an effective model for testing evolutionary hypotheses, such as how the changes in the spinal cord made it possible for the creature's ancestors to evolve from aquatic to terrestrial locomotion.
To build the Pleurobot they used advanced cineradiography to accurately map the biological design of real salamanders; recording three-dimensional X-rays of the creatures walking on ground, under water, and swimming. By tracking up to 64 points on the animal's skeleton, they were able to work out which joints were active and passive at any given time in order to reproduce its movements in 3D computer models. This was then recreated in robotic form, with the robotic joints responding the same way that the joints and muscles of a real salamander do.
The engineers call Pleurobot one of the most accurate robotic animals ever. According to Ijspeert, "we could really record all these bone motions; extract that information on a computer to have all the data of the bone motion. And then make probably the robot that's the closet to an animal ever, I would say. It's really kind of unique to be able to replay as closely the walking data and the swimming data and other types of behavior."
Pleurobot's design, which has 27 degrees of freedom, also lets scientists test more advanced mathematical models of the locomotor nervous system toward richer motor skills. Ijspeert said their main goal was gaining a better understanding of the complex workings of the human spinal cord. "By decoding this primitive animal what we hope is to also contribute to the understanding of how mammals, including humans, walk. And therefore understanding input and output relationships of the spinal cord," he said.
The researchers hope it will give neuroscientists an accurate model to test theories, including identifying how control signals are received by the spinal cord. This, they hope, could help with the development of therapies to stimulate the spinal cord of paraplegic patients.
"This type of research is very important to be the guidance research to see how you could stimulate the spinal cord, re-induce locomotion in possibly paraplegic patients in the long run. So this fundamental understanding of spinal cord functioning is very important from a medical point of view."
Pleurobot's unique design, including its low center of mass and segmented legs, means it could also have applications as a search and rescue robot because of its ability to navigate rough terrain without losing balance. Ijspeert's team are now working on a smaller model based on the Pleurobot that could fit into small spaces and relay information to search and rescue teams. Like its big brother, Ijspeert says the miniature model will also be able to operate on both land and in water.
"We're now making an amphibious robot that will have the same swimming and walking properties, but will be a bit more sturdy," said Ijspeert. "Here clearly there's a big interest of having a robot that can crawl, go through small spaces, can swim a bit. And if you have a collapsed building; you think there are survivors, you will not send a dog because maybe the building is too dangerous. It may be very interesting to have an amphibious robot that you remote control; see if there are survivors and decide then if it's worth sending a team or not."
Pleurobot was recently presented at the 5th Annual Bay Area Science Festival in San Francisco.