A new generation of underwater bots that draw from the movements of sharks, sea turtles and fish could lead to lifelike prosthetics, tough amphibious explorers and super-stealth surveillance vessels.
The recent boom in robotic fish development has been spurred in part by military strategies, environmental conservation and the oil industry. As a result, collaborations are creating a promising new generation of aquatic and tough terrain robots.
"There are some really interesting puzzles about the way that fish swim, and you can test those puzzles by trying to build robots," said John Long, a professor of biology and cognitive science at Vassar College leading work on artificial vertebral columns inspired by marine animals.
The latest issue of the Marine Technology Society's scholarly publication MTS Journal features several bio-inspired robotics, including ones developed by Long and colleagues from the University of Washington, the University of California, the University of Bergen, and the biomaterial company MiMedx Group.
Long, along with a small group of researchers, are studying biology and evolution with the aid of robots that can swim through water and slither up walls or mountains. Long's robots, for instance, test theories on the development of stiffer backbones. These bots, the researchers hope, will catch on as technological advances that mimic animals. Robot builders still use computer simulations to complement their work, but swimming robots have advantages over computer simulations since it's extremely difficult to simulate the interaction between a flexible solid — like a tail — and a liquid.
The team focused on the backbone because that is what enables the powerful undulations in cartilaginous fishes such as skates, stingrays, and sharks. Sharks were predators 300 million years ago and they're predators now, Long said. "Whatever they do works for them."
There are numerous challenges to creating a functional biomimetic vertebral column, including being able to combine viscosity with an elastic spring-like component that passively controls the dynamic motion of a system. Long compared it to bending a stack of pennies without having them all spill out.
"We're using water as a structural material when we're working with these hydrated systems," he said.
The scientists created two classes of vertebral columns. One was made by roping porous plaster parts infused with adhesive together with horse hairs, and the other was milled from thermoplastic that was set in a ring of hydrogels. They were able to propel autonomous aquatic robots shaped like an electric ray, called Tadro4, with an artificial vertebral column.
Having an understanding of the biomechanics opens up new possibilities, Long said. Mimicking negatively buoyant electric rays could make for stealthier, low-energy underwater surveillance. Their findings also open the door to fabricating artificial fibers from the molecule up and even building new prosthetic devices.
Naomi Kato is a professor in Osaka University's Graduate School of Engineering who sees a need for a robot that can conduct dangerous environmental shoreline monitoring work usually undertaken by humans on foot and in boats. He notes that the safety risks are high due to breaking waves and rip currents.
"This is a different idea for a robot," he said.
Kato and his colleagues looked to the sea turtle for inspiration, creating an amphibious robot prototype with four flipper-like mechanical arms that can both paddle and shuffle through sand.
Although the current prototype struggled to walk on land due to its weight, Kato said he plans to work on a lighter-weight one. The tsunami in Japan changed the environments along coastal areas, so an amphibious bot could be helpful in measuring the new conditions, he added.
Aquatic robots need an effective means to maneuver, but there aren't many technologies available to make artificial fins that can move with a high level of dexterity. They're usually too bulky. So Professor Kwang Kim and associate professor Kam Leang in the University of Nevada, Reno’s Department of Mechanical Engineering worked on improving propulsion.
They developed a novel electrode pattern to bend a special material called ionic polymer-metal composite, or IPMC. The material makes for an ideal fin since it can flex and work in water. Activating specific regions on the artificial fin makes it twist for better propulsion.
"Imagine trying to build a tiny robotic fish that's probably no bigger than your cell phone," said Leang. "This material we work with and the way the electrodes are patterned, you can get all that motion in a very compact and lightweight package."
Kim and Leang were able to propel and maneuver small robotic fish with the new fins. Since the material can be manipulated in aqueous solutions, Leang says the technology could eventually be used in artificial organs and to make heart valves.
Sharon Swartz is a professor of ecology and evolutionary biology at Brown University who collaborates with engineers to develop robotics inspired by bats. She said that bio-inspired robotics picked up the pace in the past two years, and that a joint meeting between Air Force and Navy researchers in April also helped.
"They've gone far beyond the surface appearance to digging into the real biology," she said. Instead of just mimicking the outer shape, scientists are looking at animals' chemical and electro-physiological functionality.
"We're coming into an era where we'll be able to harvest the fantastic designs that evolution has created over millions of years," Swartz said. "This is just the very beginning."