A man-made fish powered by heart cells
(3 minute read)
If you were an architect designing a building, you would need to know everything about the materials used to build it. That way you know if it will carry the loads it needs to hold.
If you were an engineer designing a human organ made of living cells, you would want to know everything you could about the biological materials involved and how they perform their functions.
That’s why Prof. Kit Parker and his bioengineering group at Harvard created tiny fish that are powered by the contractions of human heart cells. Their results were published in Science February 2022. [i]
“We were practicing to build a heart by building a fish,” Prof. Parker says. “We used the same cells, we used the same biophysics, and we built a muscular pump.”
Left: Diagram of fish design with stiff man-made head and fins, flexible tail with heart muscle cells on both sides. The G-node acts as the pacemaker, similar to the sinoatrial node in a human heart.
Right: Photograph of a fabricated fish capable of swimming on its own for 108 days.
They made several half-inch-long fish out of stiff paper, buoyant plastic, and flexible gelatin. They grew heart muscle cells on both sides of the gelatin tail. When they put these fish in a solution containing the right amount of salt and nutrients, the muscle cells started to twitch.
Here’s the really cool part. When one side of the tail contracts, the other side is stretched. This stretch triggers an electrical signal that tells the second muscle to contract, so the bend in the fish’s body reverses. This is a feedback loop that keeps the tail flicking side to side without any help from the outside. This movement propels the fish forward in the water.
This fish is an example of a biohybrid, a man-made device that incorporates living cells in its design. Since muscle tissue can work efficiently on very small scales, biohybrids are an active area of research for tiny robots.[ii]
“That’s the fun thing about writing a paper like this,” Prof. Parker adds. Everybody sees something different here… I look at this as a muscular pump like the heart. The marine biomechanists looked at this as a model for marine locomotion. The robotics people see this as a robot.”
Parker and his colleagues are already putting the findings from this project to good use. In particular, a design feature called the G-node, which is a little outcropping of tissue. This acts as a focal point for the electrical signals that heart muscle cells send to each other, regulating the contractions like a pacemaker. (In human hearts, this is accomplished by a similar structure called the sinoatrial node.)
They are now able to take stem cells from children with cardiomyopathy (a disease of the heart muscle), and create organ models in petri dishes to test drugs that might work for that patient. Prof. Parker again: “Some of the lessons learned, especially the G-node, we’ve already started using that… to fight pediatric heart disease.”
“We’ll never build another fish again,” he says. “We’re ready to move on to the next big thing in terms of building a muscular pump.”
Image: Time lapse of a biohybrid fish swimming autonomously.
Video available at: https://www.youtube.com/watch?v=kmCJFvRa20o
[i] Lee, Park, et. al. An autonomously swimming biohybrid fish designed with human cardiac biophysics. SCIENCE, 10 Feb 2022. Vol 375, Issue 6581. pp. 639-647. DOI: 10.1126/science.abh0474
[ii] Ricotti, et. al. Biohybrid actuators for robotics: A review of devices actuated by living cells. SCIENCE ROBOTICS, 22 Nov 2017. Vol 2, Issue 12. DOI: 10.1126/scirobotics.aaq0495
