Heart muscle helps cyborg jellyfish come alive

Even before a jolt of electricity was applied to animate its body, the cyborg twitched with signs of life. No, this isn't a scene from Frankenstein but a lab at Harvard University where the world's first artificial jellyfish has been created. With a single pulse of electricity, it even swims like the real thing.

Called a medusoid, after the umbrella-shaped class of jellyfish it mimics, the silicone cyborg uses heart muscle cells from a rat to recreate the pumping motion of the moon jellyfish, Aurelia aurita. When video of the medusoid is shown alongside that of the real thing, the similarity is startling.

"It's a bit eerie," says Kit Parker of Harvard, who created the jellyfish with colleagues at the California Institute of Technology in Pasadena. "But the strangest science is often the most awe-inspiring. The first time we got it to work and swim across a dish by itself was a big moment for us."

The work has a serious aim. Parker's team hope to help the search for novel drugs to treat heart problems by studying how differently shaped structures in the heart make heart muscle work in different ways. "Current drug discovery does not take into account [heart] structure, yet heart disease causes structural changes that lead to dysfunction," he says.

Parker was inspired by the similarity between the pumping heart muscle tissue he had seen in the lab and the jellyfish propulsion he saw while visiting the New England Aquarium in Boston. "I then knew I could build a jellyfish," he says. It was tougher than he thought, however, and took four years to perfect.

Medusoid mould

To build the medusoid, the team made a mould based on a 3D computer model of a juvenile jellyfish just 6 millimetres across. They then coated the mould with heart muscle cells from a rat, lining them up in such a way that the alignment of the fibre networks in the muscle matched that of the fibres in the jellyfish. Next they coated it in a thin layer of a liquid silicone polymer.

Once the coating had set, the medusoid could be peeled off the mould with its rat muscle network intact. All this occurred in a solution of magnesium and glucose-rich water, which kept the rat cells fed.

Sometimes the medusoid was already moving in an uncoordinated way when peeled off the mould. But applying a short 1 Hertz alternating current to the solution set it going in a realistic way ? without the need for any extra power ? for up to an hour. Each contraction of the heart muscle makes the artificial jellyfish's body suddenly bend, propelling it forward. The rubber body then slowly regains its initial shape, before contracting again.

"We found both the spatial arrangement of the rat heart cells and the electrical stimulation frequency affect propulsion," says Parker. The team now plans to mimic other marine organisms with "elegant muscular structures".

The medusoids are "ingenious", says Che Connon, who is developing tissue-engineered artificial corneas at the University of Reading in the UK. Biotech labs could use the cyborgs as filters, he says, with possible larger scale uses. "I could easily imagine medusoids used in large numbers to clean up oil spills in a similar manner to the way a jellyfish filters out its food," he adds.

The medusoid technology could also be used as implants in the human body powered by the nutrients in body fluids. One example might be as a pacemaker to replace the metal, battery-powered devices of today.

Journal reference: Nature Biotechnology, DOI: 10.1038/nbt.2269

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