Heart disease – the leading cause of death in the United States – is so deadly in part because the heart, unlike other organs, cannot repair itself after injury. This is why tissue engineering, including the wholesale manufacturing of an entire human heart for transplantation, is so important to the future of cardiac medicine.
To build a human heart from scratch, researchers must replicate the unique structures that make up the heart. This includes the recreation of helical geometries, which create a twisting motion when the heart beats. This twisting motion has long been theorized to be essential for pumping blood at high volumes, but proving this has been difficult, in part because creating hearts with different geometries and alignments has been difficult.
Now the bioengineers of Harvard John A. Paulson School of Engineering and Applied Science (SEAS) developed the first biohybrid model of human ventricles with beating heart cells aligned in a helix, and showed that muscle alignment actually dramatically increases the amount of blood the ventricle can pump with each contraction.
This breakthrough was made possible by a new additive textile manufacturing method, 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 GroupFRJS fibers drive cellular alignment, allowing the formation of controlled tissue-engineered structures.
The research is published in Science.
“This work is a major breakthrough for organ biofabrication and brings us closer to our ultimate goal of constructing a human heart for transplantation,” said Parker, Tarr Family Professor of Bioengineering and Applied Physics at SEAS and lead author. of the item.
This work has its roots in a centuries-old mystery. In 1669, the English physician Richard Lower – a man who counted John Locke among his colleagues and King Charles II among his patients – first noted the spiral arrangement of heart muscles in his seminal work. Rope Tractatus.
Over the next three centuries, doctors and scientists built a more complete understanding of the structure of the heart, but the purpose of these spiral muscles remained extremely difficult to study.
In 1969, Edward Sallin, former head of the department of biomathematics at the University of Alabama Birmingham School of Medicine, argued that the helical alignment of the heart is essential for achieving large ejection fractions – the percentage of the amount of blood the ventricle pumps with each contraction.
“Our goal was to build a model where we could test Sallin’s hypothesis and investigate the relative importance of the helical structure of the heart,” said John Zimmerman, 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 heart cells.
The first stage of FRJS works like a cotton candy machine – a liquid polymer solution is charged into a reservoir and forced out through a tiny opening by centrifugal force as the device spins. When the solution leaves the reservoir, the solvent evaporates and the polymers solidify to form fibers. Then, a focused airflow controls the orientation of the fiber as it is deposited on a collector. The team found that by tilting and rotating the collector, the flow fibers aligned and twisted around the collector as it rotated, mimicking the helical structure of heart muscles.
The alignment of the fibers can be adjusted by changing the angle of the collector.
“The human heart actually has multiple layers of muscles aligned in a helix with different angles of alignment,” said Huibin Chang, postdoctoral fellow at SEAS and co-first author of the paper. “With FRJS, we can recreate these complex structures very precisely, forming single or even four chamber ventricle structures.”
Unlike 3D printing, which slows down as features get smaller, FRJS can quickly spin fibers at the scale of one micron – about fifty times smaller than a single human hair. This is important when it comes to building a heart from scratch. Take collagen, for example, a protein in the extracellular matrix of the heart, which is also one micron in diameter. It would take over 100 years to 3D print every piece of collagen in the human heart at this resolution. FRJS can do it in a single day.
After rotation, the ventricles were seeded with rat cardiomyocytes or human stem cell-derived cardiomyocyte cells. Within about a week, several thin layers of flapping tissue covered the scaffold, the cells following the alignment of the fibers below.
The beating ventricles mimicked the same twisting or spinning motion present in the human heart.
The researchers compared ventricle strain, electrical signaling velocity, and ejection fraction between ventricles made of helically aligned fibers and those made of circumferentially aligned fibers. They found that on all fronts, helically aligned tissue outperformed circumferentially aligned tissue.
“Since 2003, our group has worked to understand the structure-function relationships of the heart and how disease pathologically compromises these relationships,” Parker said. “In this case, we came back to address a never-before-tested observation of the helical structure of the heart. Fortunately, Professor Sallin published a theoretical prediction more than half a century ago and we were able to construct a new manufacturing platform that allowed us to test his hypothesis and answer this age-old question.
The team also demonstrated that the process can be scaled up to the size of an actual human heart and even larger, to the size of a minke whale heart (they didn’t seed the larger models with cells because it would take billions of cardiomyocyte cells).
Besides biofabrication, the team is also exploring other applications for their FRJS platform, such as food packaging.
The Harvard Technology Development Office has protected the intellectual property relating to this project and is exploring commercialization possibilities.
This work was co-authored by Qihan Liu, Keel Yong Lee, Qianru Jin, Michael M. Peters, Michael Rosnach, Suji Choi, Sean L. Kim, Herdeline Ann M. Ardoña, Luke A. MacQueen, Christophe O. Chantre, Sarah E. Motta and Elizabeth M. Cordoves.
It was supported in part by the Harvard Materials Research Science and Engineering Center (DMR-1420570, DMR-2011754), the National Institutes of Health with the Center for Nanoscale Systems (S10OD023519), and the National Center for Advancing Translational Sciences (UH3TR000522, 1-UG3-HL-141798-01).
The title of the article
Recreate the helical structure-function relationship of the heart with focused rotary jet spinning
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