Those drifting moon jellyfish at the aquarium may not seem like they have much purpose in life, but  one group of researchers has been looking to make a jelly-inspired underwater robot that could go on search- and-rescue missions and survey for the military. 

 

Now the team, funded by the U.S. Office of Naval Research, has created a silicon Robojelly that uses hydrogen and oxygen for fuel as it swims, so its only "exhaust" is heat and water. They published their findings March 20 in the journal Smart Materials and Structures.

 

Robojelly's muscles are made of a shape-memory alloy, a metal invented by NASA that "remembers" its original shape. Shape-memory alloys have been used to make orthodontic braces that keep their shape and glasses frames that return to their original shape after getting bent if they're warmed. In this case, the Robojelly muscles contract when heated, propelling the robot through water, just like a living jellyfish.

 

The heat needed for the robotic jellyfish comes from a clever chemical reaction at the surface of its metal muscles. The muscles are covered with nanofibers of carbon dusted with platinum. To get the Robojelly started, the researchers inject its top with hydrogen and oxygen fuel. When the fuel comes in contact with the platinum, they create a hot combustion reaction, plus water as a waste product. When the muscles cool, they relax and the Robojelly's bell-shaped body fills with water, ready for the next contraction. 

 

Besides being a non-polluting energy source, hydrogen and oxygen fuel is more energy-dense than batteries, so the robot could carry more power with it, the researchers, including engineers from Virginia Tech and the University of Texas at Dallas, wrote in their paper. In fact, one day, RoboJelly might not even need to carry fuel with it at all, as it's made to swim in water and water is made of molecules of hydrogen and oxygen. At the moment, however, it cannot use the hydrogen and oxygen in water molecules and still depends on a fuel injection. 

 

Jellyfish may look lackadaisical, but, as the team wrote in a 2009 paper introducing their original idea for a jellyfish robot, the animals are actually efficient swimmers, have few natural predators, work well in many sizes and are shaped just right to carry loads, making them ideal for underwater robots. 

 

Watch Robojelly pulsing its way up a testing tank:

 

 

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