Scientists from Harvard and Caltech announce the creation of a bioengineered, swimming jellyfish made from rat cells.

You begin with an eight-armed silicon membrane. You harvest rat heart-muscle cells and organize them in a disctinct jellyfish-like pattern on your membrane. Lastly, you set your creature free in a vat of fluid, and schock it with electricity. You watch as your "jellyfish" swims away.

Scientists from Harvard and Caltech did just that, and they are calling their rat-celled, bioengineered jellyfish a "medusoid." They hope that by studying its pumping motions, they will be able to extrapolate a better understanding of another pump -- the human heart. Their paper appeared in an advance online version today in Nature Biotechnology.

As Ed Yong reports:

"Morphologically, we've built a jellyfish. Functionally, we've built a jellyfish. Genetically, this thing is a rat," says Kit Parker, a biophysicist at Harvard University in Cambridge, Massachusetts, who led the work.

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In 2007, Parker was searching for new ways of studying muscular pumps when he visited the New England Aquarium in Boston, Massachusetts. "I saw the jellyfish display and it hit me like a thunderbolt," he says. "I thought: I know I can build that." To do so, he recruited John Dabiri, a bioengineer who studies biological propulsion at the California Institute of Technology (Caltech) in Pasadena. "I grabbed him and said, 'John, I think I can build a jellyfish.' He didn't know who I was, but I was pretty excited and waving my arms, and I think he was afraid to say no."

Janna Nawroth, a graduate student at Caltech who performed most of the experiments, began by mapping every cell in the bodies of juvenile moon jellies (Aurelia aurita) to understand how they swim. A moon jelly's bell consists of a single layer of muscle, with fibres that are tightly aligned around a central ring and along eight spokes.

To make the bell beat downwards, electrical signals spread through the muscle in a smooth wave, "like when you drop a pebble in water", says Parker. "It's exactly like what you see in the heart. My bet is that to get a muscular pump, the electrical activity has got to spread as a wavefront."

Down the road, the team plans to build a medusoid that uses human heart cells, Yong reports. "You've got a heart drug?" Parker told Yong. "You let me put it on my jellyfish, and I'll tell you if it can improve the pumping."