Media playback is unsupported on your device Media caption The artificial jellyfish replica is made from silicone polymer and rat heart cells

Scientists in the US have created a free swimming artificial jellyfish.

The team members built the replica using silicone as a base on which to grow heart muscle cells that were harvested from rats.

They used an electric current to shock the Medusoid into swimming with synchronised contractions that mimic those of real jellyfish.

The advance, by researchers at Caltech and Harvard University, is reported in the journal Nature Biotechnology .

The finding serves as a proof of concept for reverse engineering a variety of muscular organs and simple life forms.

Because jellyfish use a muscle to pump their way through the water, the way they function - on a very basic level - is similar to that of a human heart.

"I started looking at marine organisms that pump to survive," said Kevin Kit Parker, a professor of bioengineering and applied physics at Harvard.

"Then I saw a jellyfish at the New England Aquarium, and I immediately noted both similarities and differences between how the jellyfish pumps and the human heart.

"The similarities help reveal what you need to do to design a bio-inspired pump."

Mechanical movement

The work also points to a broader definition of "synthetic life" in an emerging field of science that has until now focused on replicating life's building blocks, say the researchers.

Prof Parker said he wanted to challenge the traditional view of synthetic biology which is "focused on genetic manipulations of cells". Instead of building just a cell, he sought to "build a beast".

The two groups at Caltech and Harvard worked for years to understand the key factors that contribute to jellyfish propulsion, including the arrangement of their muscles, how their bodies contract and recoil, and how fluid dynamics helps or hinders their movements.

Image caption The swimming behaviour of the Medusoid closely mimics that of the real thing

Once these functions were well understood, the researchers began to reverse engineer them.

They used silicone to fashion a jellyfish-shaped body with eight arm-like appendages.

Next, they printed a pattern made of protein onto the "body" that resembled the muscle architecture of the real animal.

They grew the heart muscle cells on top, with the protein pattern serving as a road map for the growth and organisation of the rat tissue. This allowed them to turn the cells into a coherent swimming muscle.

When the researchers set the Medusoid free in a container of electrically conducting fluid, they shocked the Medusoid into swimming with synchronised contractions. The muscle cells even started to contract a bit on their own before the electrical current was applied.

"I was surprised that with relatively few components - a silicone base and cells that we arranged - we were able to reproduce some pretty complex swimming and feeding behaviours that you see in biological jellyfish," said John Dabiri, professor of aeronautics and bioengineering at Caltech.

"I'm pleasantly surprised at how close we are getting to matching the natural biological performance, but also that we're seeing ways in which we can probably improve on that natural performance. The process of evolution missed a lot of good solutions."

Lead author Janna Nawroth from the California Institute of Technology (Caltech) in Pasadena commented that the field of tissue engineering was "still a very qualitative art".

She said researchers tried to copy a tissue or organ "based on what they think is important or what they see as the major components without necessarily understanding if those components are relevant to the desired function or without analysing first how different materials could be used".

The team aims to carry out further work on the artificial jellyfish. They want to make adjustments that will allow it to turn and move in a particular direction.

They also plan to incorporate a simple "brain" so it can respond to its environment and replicate more advanced behaviours like moving towards a light source and seeking energy or food.