Future bio-inspired pacemaker may require no batteries to pump

A team led by researchers at the California Institute of Technology (Caltech) and Harvard University have turned a solid element—silicon—and muscle cells into a freely swimming “jellyfish.” Their tissue-engineered jellyfish has been dubbed as Medusoid. “A big goal of our study was to advance tissue engineering,” said Janna Nawroth, a doctoral student in biology at Caltech and lead author of the study. “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 analysing first how different materials could be used,” she noted. Because a particular function—swimming, say—doesn`t necessarily emerge just from copying every single element of a swimming organism into a design, “our idea,” she pointed out, “was that we would make jellyfish functions—swimming and creating feeding currents—as our target and then build a structure based on that information.” Jellyfish are believed to be the oldest multi-organ animals in the world, possibly existing on Earth for the past 500 million years. Because they use a muscle to pump their way through the water, their function—on a very basic level—is similar to that of a human heart, which makes the animal a good biological system to analyze for use in tissue engineering.“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,” said Kevin Kit Parker, Tarr Family Professor of Bioengineering and Applied Physics at Harvard and a coauthor of the study. Parker contacted John Dabiri, professor of aeronautics and bioengineering at Caltech—and Nawroth`s advisor—and a partnership was born. Together, the two groups 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-dynamic effects help or hinder their movements. Once these functions were well understood, the researchers began to design the artificial jellyfish. The team at Harvard—with the help of Nawroth, who spent time on both campuses during the length of the project—fashioned the silicone polymer that makes up the body of the Medusoid into a thin membrane that resembles a small jellyfish, with eight arm-like appendages. Next, they printed a pattern made of protein onto the membrane that resembled the muscle architecture in the real animal. 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. When the researchers set their creation free in an electrically conducting container of fluid and oscillated the voltage from zero volts to five, they shocked the Medusoid into swimming with synchronized contractions that mimic those of real jellyfish. In fact, the muscle cells started to contract a bit on their own even 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 Dabiri, with fluid-dynamics measurements that match up to those of the real animal. This advance in bio-inspired engineering, the team noted, demonstrates that it is inadequate to simply mimic nature: the focus must be on function. Their design strategy, they say, will be broadly applicable to the reverse engineering of muscular organs in humans. In addition, Dabiri and colleagues pointed out that, their new process of harvesting heart-muscle cells from one organism and reorganizing them in an artificial system will be useful in building an engineered system using biological materials. The team``s next goal is to design a completely self-contained system that is able to sense and actuate on its own using internal signals, as human hearts do. Nawroth and Dabiri would also like for the Medusoid to be able to go out and gather food on its own. Then, researchers could think about systems that could live in the human body for years at a time without having to worry about batteries because the system would be able to fend for itself. For example, these systems could be the basis for a pacemaker made with biological elements. Their method for building the tissue-engineered jellyfish has been outlined in a Nature Biotechnology paper that appeared as an advance online publication. ANI