Hydrogen-powered robotic jellyfish takes shape

Researchers at Virginia Tech and the University of Texas at Dallas have created Robojelly, a hydrogen-powered robotic jellyfish that could be used in underwater search-and-rescue operations.

Robojelly has been built from carbon nanotubes and materials that change shape or size as a result of a stimulus, which gives it the ability to mimic the natural movements of a jellyfish in water. Furthermore, it is powered by chemical reactions taking place on its surface.

‘To our knowledge, this is the first successful powering of an underwater robot using external hydrogen as a fuel source,’ said lead author of the study Yonas Tadesse, a professor at the University of Texas at Dallas.

The creators of Robojelly presented their results in the 21 March issue of IOP Publishing’s journal Smart Materials and Structures.

According to a statement, the jellyfish is an ideal invertebrate to base the vehicle on due to its simple swimming action: it has two prominent mechanisms known as ‘rowing’ and ‘jetting’.

A jellyfish’s movement is attributed to circular muscles located on the inside of the bell — the main part of the body shaped like the top of an umbrella. As the muscles contract, the bell closes in on itself and ejects water to propel the jellyfish forward. After contracting, the bell relaxes and regains its original shape.

This was replicated in the vehicle using commercially available shape memory alloys (SMA) — smart materials that ‘remember’ their original shape — wrapped in carbon nanotubes and coated with a platinum black powder.

The robot is powered by heat-producing chemical reactions between the oxygen and hydrogen in water and the platinum on its surface. The heat given off by these reactions is transferred to the artificial muscles of the robot, causing them to transform into different shapes.

This means Robojelly can regenerate fuel from its natural surroundings and does not require an external power source or the constant replacement of batteries.

The hydrogen-powered Robojelly has been functioning while being clamped down in a water tank. The researchers said that the robot still needs development to achieve full functionality and efficiency.

Tadesse said: ‘The current design allows the jellyfish to flex its eight bell segments, each operated by a fuel-powered SMA module. This should be sufficient for the jellyfish to lift itself up if all the bell segments are actuated.

‘We are now researching new ways to deliver the fuel into each segment so that each one can be controlled individually. This should allow the robot to be controlled and moved in different directions.’