We’re closer to the artificial heart

Cross-sectional view of the human heart Image source: matis75/

To build a human heart from scratch, researchers need to replicate the unique structures that make up the heart. This includes reconstructing the spiral geometry, which creates distorted movements when the heart beats. This twisted movement has long been thought to be essential for drawing blood in large quantities, but this has proven difficult, in part because creating hearts with different geometries and arrangements is challenging.

Now, bioengineers at Harvard’s John Paulson School of Engineering and Applied Sciences (SEAS) have developed the first human model of ventricular biology hybridization with a spiral arrangement of beating heart cells using a new additive textile manufacturing method, and show that muscle alignment does significantly increase the amount of blood that the ventricles can pump out each contraction. The findings were published in Science on July 7.

Study corresponding author Kevin Kit Parker, a Professor of Bioengineering and Applied Physics at SEAS’s Tarr Family, said this work is an important step forward in organ biomaking, bringing us closer to the ultimate goal of establishing a human heart for transplantation.

John Zimmerman, a SEAS postdoctoral researcher and co-first author of the paper, said the goal of the study was to build a model that would test whether the spiral alignment of the heart is critical to reaching a large ejection fraction (i.e., the percentage of blood pumped by the ventricles at each contraction) and to study the relative importance of the heart’s spiral structure.

The researchers used the FRJS system to control the alignment of the spun fibers, on which they could grow heart cells. The first step of the FRJS is like a marshmallow machine – a liquid polymer solution is loaded into the reservoir and pushed out of a small opening by centrifugal force as the device rotates. When the solution leaves the reservoir, the solvent evaporates and the polymer solidifies to form fibers. The focused airflow then controls the direction in which the fibers are deposited on the collector. The researchers found that by tilting and rotating the collector, the fibers in the stream align and twist as the collector rotates, mimicking the spiral structure of the myocardium, and changing the angle of the collector adjusts the alignment of the fibers.

Huibin Chang, a postdoctoral researcher at SEAS and co-first author of the paper, said that the human heart actually has multiple layers of spiral alignment muscles, and the arrangement angles are different. Using FRJS, these complex structures can be reconstructed in a very precise way, forming a single or even four chamber structures.

Unlike 3D printing, FRJS can quickly rotate fibers in a single micron scale, or about 50 times smaller than a single human hair. This is important when it comes to building a heart from scratch. Take collagen as an example, at this resolution, 3D printing every bit of collagen in the human heart takes more than 100 years, and FRJS can be done in a day.

After spinning, the researchers implanted rat cardiomyocytes or human stem cell-derived cardiomyocytes in the ventricles, respectively. In about a week, several thin layers of beating tissue are covered on the scaffold, and the cells are aligned along the underlying fibers. The beating ventricles mimic the same twisted movements in the human heart.

The researchers compared ventricle deformation, electrical signal velocity, and ejection fraction between ventricles made of spiral-aligned fibers and ventricles made of circumferentially aligned fibers. They found that in each respect, spiral-aligned tissue performed better than circumferentially aligned tissue.

The team also demonstrated that this process can be extended to the size of an actual human heart, or even as large as the size of a minke whale’s heart. In addition to biomanufacturing, the team explored other applications of the FRJS platform, such as food packaging. (Source: China Science Daily Xin Yu)

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