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Ghost Hearts

Author: Ruoxi Lin

Editors: Flynn Ma and Ken Saito

Artist: Carys Chan

It’s a well-known fact that the heart is one of the most vital organs in our body for survival, which makes the diseases that compromise it all the more deserving of medical attention and research. Cardiologists and biomedical engineers work tirelessly on new heart treatments and technologies that can combat the effects of common diseases such as arrhythmias (irregular heart beating) and coronary artery disease (damage to the heart’s arteries). Trusty devices called pacemakers help generate electrical pulses to help adjust the heart’s rhythm. At the same time, angioplasty, a procedure that inserts a balloon in the arteries, helps restore blood flow to the heart. In recent years, when medical breakthroughs have been at their peak, the seemingly impossible idea of a successful, totally artificial heart transplant may become a reality for patients around the world.

The term “ghost hearts” has been used to describe Doris Taylor and her team’s recent project. Created in the Texas Heart Institute labs, these artificial hearts are animal hearts that have undergone decellularization– the process of removing cells of living tissue to produce an extracellular matrix (ECM) scaffold– before being injected with hundreds of millions of stem cells. Stem cells are self-renewable cells with the unique ability to replicate and divide into differentiated cells that recreate specific functional tissue. Taylor’s experiment used a pig heart scaffold, which researchers mostly use due to its resemblance to a human heart and its partial formation of clinically approved heart valves. The injected stem cells could transform into induced pluripotent stem cell-derived cells (iPSCs). Pluripotent refers to the viable nature of stem cells to form virtually any body part. In this case, cells split apart into ventricular cells in the ventricle and atrial cells in the atrium.

A successful, practical artificial heart must be able to contract, receive electrical signals, and deliver blood to the rest of the body. Because of this, one of the primary goals of the team was to generate enough stem cells that could produce billions of cardiomyocytes (heart muscle cells) and endothelial cells– cells that make up the endothelium, a single cell layer of tissue that lines not only our heart but also heart vessels. These two types of cells are the most prevalent, with endothelial cells accounting for over 60% and cardiomyocytes accounting for 30 % - 40 % of the heart’s cells. Another target they reached was replicating a heartbeat, which was achieved through electrical stimulation and monitoring. Typically, the heart would have specialized cells– pacemaker cells– that would send electrical impulses throughout the heart to control and maintain a cycle of rhythmic blood pumping. And if that wasn’t a lot to manage already, there is the underlying risk of accidentally contaminating the heart, which would lead to infection and eventual death.

To achieve all of this, Taylor and her team used honeycomb-like fiber– one with multiple microscopic holes that the stem cells could attach themselves to for nourishment, boosting the cell count. They also created a sterile container for the heart and used a BAB, or a BioAssemblyBot, to inject the cells in suitable locations. The heart would be hooked up to a bioreactor, a device used to help produce an environment ideal for cells to go and undergo biochemical reactions. This would enable the heart to grow in the perfect environment with the right temperature and pH and with the right amount of nutrients. Artificial lungs were also used to provide oxygen for the cells. With years of research and experimentation, under the right conditions, this high-risk, high-reward ghost heart could function and thrive for sixty days, limited only by the budget of running such an operation.

This study poses multiple questions and implications for future heart transplants and heart disease treatments. Because stem cells can be found in the brain, blood, and bone marrow, it opens the possibility of future tailor-made heart transplants that don’t risk getting rejected by the rest of the body. This would bring an end to organ shortages and save millions of dollars that would have been invested in anti-rejection drugs and therapy. However, due to the project's cost, finalizing research on it and bringing it to clinical use will still have to take a considerable amount of time. Despite this, Taylor is not discouraged– opting to focus on funding her study and hoping that her lab-created method can one day be used to create artificial hearts that can change the lives of those with heart disease.



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