The authors expect their technology will eventually lead to the harvesting of cells from one organism, rearranging them so they may be bioengineered for use in humans, such as making a heart pacemaker with no battery.
Janna Nawroth, a doctoral student in biology at Caltech and lead author of the study, said:
"A big goal of our study was to advance tissue engineering. In many ways, it is still a very qualitative art, with people trying to copy a tissue or organ just 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 analyzing first how different materials could be used."
Because a specific function, such as swimming for example, does not automatically emerge simply from copying all the elements of a swimming organism into a design, their idea was to make jellyfish functions - swimming in water and making feeding currents - as their target, and then create a structure based on that data.
Jellyfish are thought to have been around for the last 500 million years; they are probably the oldest multi-organ animals on Earth. Jellyfish are good animals to research when attempting to find ways of fixing heart problems, the authors wrote. On a very basic level, their function is similar to that of a human heart in that they use a muscle to pump their way through water.
Co-author, Kevin Kit Parker, Tarr Family Professor of Bioengineering and Applied Physics at Harvard, said:
"It occurred to me in 2007 that we might have failed to understand the fundamental laws of muscular pumps. I started looking at marine organisms that pump to survive. 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."
Parker got in touch with aeronautics and bioengineering expert John Dabiri from Caltech, and formed a partnership. The two groups liaised closely for several years, trying to get a better understanding of the intricacies of jellyfish propulsion, including how their muscles are arranged, how their bodies contract and then recoil, and the impact of fluid-dynamics on their movements. They then set out to design an artificial jellyfish.
Nawroth and team experimented with various different materials which could be used to make the jellyfish's body, and eventually opted for an elastic material that is very similar to the "jelly" of real jellyfish flesh.
The Harvard team, with Nawroth's help, fashioned the silicone polymer that forms the Medusoid body into a thin membrane that is similar to a small jellyfish, with eight feeler-like arms. They then printed a pattern made of a protein onto the membrane that was like the muscle structure of the real animal. The authors explained that "The protein pattern serves as a road map for growth and organization of dissociated rat tissue - individual heart muscle cells that retain the ability to contract - into a coherent swimming muscle."
The Medusoid was then placed in an electrically conducting container of fluid, and oscillated the voltage from zero to five volts, shocking the new creature into swimming with contractions just like a jellyfish. Even before applying the electrical current, the muscle cells had already started contracting a bit on their own.
Dabiri said the team was surprise that they could reproduce such complex swimming and feeding behaviors that so closely resembled biological jellyfish with relatively few components - a silicone base and rearranged rat cells. The fluid-dynamics measurements were virtually identical to those of natural jellyfish.
"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."
You have to concentrate on functionTheir breakthrough shows that you cannot just mimic nature, you have to concentrate on function. Their design strategy could be applied, in general, to the reverse engineering of muscular organs in the human body, the scientists explained.
"As engineers, we are very comfortable with building things out of steel, copper, concrete. I think of cells as another kind of building substrate, but we need rigorous quantitative design specs to move tissue engineering from arts and crafts to a reproducible type of engineering. The jellyfish provides a design algorithm for reverse engineering an organ's function and developing quantitative design and performance specifications. We can complete the full exercise of the engineer's design process: design, build, and test."
The scientists now plan to design a totally self-contained system that can sense and actuate on its own, using internal signals, just like the human heart does.
Dabiri and Nawroth say Medusoid should eventually be able to seek out and gather its own food independently. Scientists could then create systems that could exist in the human body for years without the need for batteries, because they would have the ability to fend for themselves. These systems could, for example, be the basis for a pacemaker made purely with biological elements.
"We're reimagining how much we can do in terms of synthetic biology. A lot of work these days is done to engineer molecules, but there is much less effort to engineer organisms. I think this is a good glimpse into the future of re-engineering entire organisms for the purposes of advancing biomedical technology. We may also be able to engineer applications where these biological systems give us the opportunity to do things more efficiently, with less energy usage."