Heart disease -- the leading cause of death in the U.S. -- is so deadly in part because the heart, unlike other organs, cannot repair itself after injury. That is why tissue engineering, ultimately including the wholesale fabrication of an entire human heart for transplant, is so important for the future of cardiac medicine.
To build a human heart from the ground up, researchers need to replicate the unique structures that make up the heart. This includes recreating helical geometries, which create a twisting motion as the heart beats. It's been long theorized that this twisting motion is critical for pumping blood at high volumes, but proving that has been difficult, in part because creating hearts with different geometries and alignments has been challenging.
Now, bioengineers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed the first biohybrid model of human ventricles with helically aligned beating cardiac cells, and have shown that muscle alignment does, in fact, dramatically increases how much blood the ventricle can pump with each contraction.
This advancement was made possible using a new method of additive textile manufacturing, Focused Rotary Jet Spinning (FRJS), which enabled the high-throughput fabrication of helically aligned fibers with diameters ranging from several micrometers to hundreds of nanometers. Developed at SEAS by Kit Parker's Disease Biophysics Group, FRJS fibers direct cell alignment, allowing for the formation of controlled tissue engineered structures.
The research is published in Science.
"This work is a major step forward for organ biofabrication and brings us closer to our ultimate goal of building a human heart for transplant," said Parker, the Tarr Family Professor of Bioengineering and Applied Physics at SEAS and senior author of the paper.
This work has its roots in a centuries old mystery. In 1669, English physician Richard Lower -- a man who counted John Locke among his colleagues and King Charles II among his patients -- first noted the spiral-like arrangement of heart muscles in his seminal work Tractatus de Corde.
Over the next three centuries, physicians and scientists have built a more comprehensive understanding of the heart's structure but the purpose of those spiraling muscles has remained frustratingly hard to study.
In 1969, Edward Sallin, former chair of the Department of Biomathematics at the University of Alabama Birmingham Medical School, argued that the heart's helical alignment is critical to achieving large ejection fractions -- the percentage of how much blood the ventricle pumps with each contraction.
"Our goal was to build a model where we could test Sallin's hypothesis and study the relative importance of the heart's helical structure," said John Zimmerman, a postdoctoral fellow at SEAS and co-first author of the paper.
To test Sallin's theory, the SEAS researchers used the FRJS system to control the alignment of spun fibers on which they could grow cardiac cells.
The first step of FRJS works like a cotton candy machine -- a liquid polymer solution is loaded into a reservoir and pushed out through a tiny opening by centrifugal force as the device spins. As the solution leaves the reservoir, the solvent evaporates, and the polymers solidify to form fibers. Then, a focused airstream controls the orientation of the fiber as they are deposited on a collector. The team found that by angling and rotating the collector, the fibers in the stream would align and twist around the collector as it spun, mimicking the helical structure of heart muscles.
The alignment of the fibers can be tuned by changing the angle of the collector.
"The human heart actually has multiple layers of helically aligned muscles with different angles of alignment," said Huibin Chang, a postdoctoral fellow at SEAS and co-first author of the paper. "With FRJS, we can recreate those complex structures in a really precise way, forming single and even four chambered ventricle structures."
Source: ScienceDaily
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