Digital Tbucket Tank (DTT)

An important step was taken at Harvard to produce human hearts for transplant

The Heart is unable to regenerate after damage. Therefore, the efforts of tissue engineering specialists trying to develop techniques for the regeneration of the cardiac muscle to develop and in the future to create a whole heart from scratch is of great importance for cardiology and cardiac surgery. This is a difficult task, however, as unique structures must be modeled, most notably the spiral arrangement of the cells. It has long been suspected that this type of cell organization is necessary to pump sufficiently large volumes of blood.

Bioengineers from the Harvard John A. Paulson School of Engineering and Applied Sciences have succeeded in creating the first biohybrid model of a human heart chamber spirally arranged cardiac cells to create and thereby prove that the assumption was correct. This spiral arrangement of the cells significantly increases the amount of blood that is pumped with each heartbeat. This is an important step that brings us closer to the goal of building a transplantable heart from scratch," says Professor Kit Parker, one of the lead authors of the study. We can read the results on the pages of Science ...

 Image source: Pixabay; Which

The foundation for today's achievements of American scientists was laid 350 years ago by the Englishman Richard Lower. The doctor, whose patients included King Charles II, was the first to notice and describe in the Tractatus de Corde that the fibers of the heart muscle are arranged in a spiral. Over the centuries that followed, scientists learned more and more about it Heart, but studying the spiral arrangement of its cells was very difficult. In 1969, Edward Sallin of the University of Alabama School of Medicine hypothesized that it was the spiral arrangement of cells that made the heart work so efficiently. However, it was not easy to test this hypothesis since it is very difficult to compare hearts with different Geometries and fiber arrays to build.
Our goal was to build a model that would allow us to test Sallin's hypothesis and study the meaning of the spiral fiber structure," explains John Zimmerman of SEAS.

Researchers developed a method called Focused Rotary Jet Spinning (FRJS). The device works similar to a cotton candy machine. The liquid biopolymer in the tank exits through a small opening and is centrifugal forces, which act on the rotating tank, are pushed outwards. After leaving the tank, the solvent evaporates from the biopolymer and the material hardens into fibers. A precisely controlled airflow, in turn, brings the Preparation of Fibers into the right shape. By manipulating this ray, it is possible to give the fibers the correct structure that mimics that of cardiac muscle fibers. With FRJS, we can precisely replicate complex structures by creating one- and even four-chamber structures, adds Hubin Chang.

After the appropriate structures had been woven in this way, the researchers brought out rat heart muscle cells or cardiomyocytes obtained human stem cells on such a scaffold. A week later, the scaffold was covered with multiple layers of contractive and diastolic cardiac cells arranged in the same way as the biopolymer fibers.
The researchers created two cardiac cell architectures. One with fibers arranged in a spiral, the other with fibers arranged in a circle. Then they compared them deformation of the chamber, the speed of transmission of electrical signals, and the amount of blood expelled during contraction. The chamber with radially arranged fibers was found to be superior to the chamber with circular arrangement in all aspects tested.

In addition, the scientists showed that their method can be scaled up not only to the size of a human heart, but even to the size of a minke whale heart. They didn't do any testing on larger models because that's using billions of cardiomyocytes would have required.