Now Frankenstein can have a pet jellyfish. A team of scientists has taken the heart cells of a rat, arranged them on a piece of rubbery silicone, added a jolt of electricity, and created a "Franken-jelly." Just like a real jellyfish, the artificial jelly swims around by pumping water in and out of its bell-shaped body. Researchers hope the advance can someday help engineers design better artificial hearts and other muscular organs.
Young moon jellyfish (Aurelia aurita), which are usually between 10 and 12 cm wide, swim rhythmically. First, they flex their muscles quickly and all at once, expelling water as they take on a dome shape. Then, slowly, their body relaxes and flattens, triggering another round of muscle contractions. Researchers knew which cells helped jellyfish move, and how they work together to push and pull water. What they wanted to find out was how best to recreate this behavior using materials available in the lab.
Bioengineers John Dabiri from the California Institute of Technology in Pasadena, California, and Kevin Kit Parker from the Wyss Institute for Biologically Inspired Engineering at Harvard University adopted a motto: Copy nature, but not too much. "Some engineers build things out of concrete, copper and steel—we build things out of cells," says Parker.
The duo and their colleagues stenciled out the ideal jellyfish shape on silicone, a material that would be sturdy but flexible, much like the jellyfish itself. They then coached rat muscle cells to grow in parallel bands on the silicone and encased the cells with a stretchy material called elastomer. To get their artificial jellyfish, or medusoid, swimming, the researchers submerged it in a salty solution and ran an electric current through the water, jump-starting the rat cells. The mimic propelled itself rapidly in the water, swimming as effectively as a real jellyfish, the researchers report online today in Nature Biotechnology.
The team went through a lot of trial and error to get everything right, Parker notes. The silicone layer used to mimic the jellyfish's body had to be strong but not so strong that the muscle cells could not stiffen it, and the fingerlike lobes of the body had to be adjusted to make sure water could flow in between them. In healthy hearts, valves open wide and close tightly. When they malfunction, there can be serious health repercussions. By studying how jellyfish manipulate liquids with their body, Parker says, scientists may be able to come up with more accurate ways to fix or even replace damaged heart valves.
Joseph Ayers, a neurophysiologist at Northeastern University in Boston who was not involved with the study, is impressed, particularly because the researchers were able to use the energy produced by muscle cells and not batteries to power the medusoids, making them practically independent. "This is very much a landmark paper," he says. "I think in the long run, its greatest impact is going to be in implantable medical devices."
*This item has been corrected on 24 July. A team of scientists has taken the heart cells of a rat, arranged them on a piece of rubbery silicone, not silicon, to mimic a jellyfish.