Engineering a Piece of the Human Heart 

A group of people poses in a courtyard
The Gree Research Group brings together expertise in multiple disciplines in a team effort to engineer the most primitive stage of the human heart.

On a summer afternoon in 2017, eight scientists from the UW Medicine Institute for Stem Cell and Regenerative Medicine (ISCRM) gathered around a backyard grill. Under a blue sky, the conversation turned to the future of medicine. What could this team do together, they wondered, that would advance the field and transform health on a global scale?

Over hamburgers, hot dogs, and veggies, a galvanizing idea formed. Why not use their combined expertise in cardiology and engineering to do the impossible and grow the most primitive component of a human heart?

That primitive component is known as a heart tube. In the third week of gestation, stem cells in the mesoderm layer of the embryo organize themselves into a pair of tube-shaped structures that resemble blood vessels in both shape and function. These endothelial tubes grow and fold, then fuse, eventually becoming the vital organ that will pump blood rich with nutrients and oxygen to all parts of the body, one contraction at a time.

Engineering a heart tube in a lab would be a monumental feat of cooperation and complexity, requiring answers to at least three profound questions about human development. How do heart cells specialize and proliferate, eventually becoming a complete organ? What do scientists need to know and do in order to control this process? And can they use these insights to grow biological structures that look and function just like they would if they had developed naturally?

Magnified image a heart tube with purple staining
Magnified image of an engineered heart tube, the earliest stage of human heart development.

Answering these questions would have massive real-world implications. An engineered heart tube would be a game-changing learning environment, allowing scientists to study the nature of human development – and measure the efficacy of potential therapies for heart disease, the world’s leading cause of death – in ways not possible in actual patients. It would also be both a proof-of-concept and the first pages of a manual for someday growing an entire heart from stem cells.

The decision to take on this challenge – almost cosmic in scope – was made on the spot. The prospect of forging the future of heart research, and pioneering new treatments for heart disease was a call to action the scientists couldn’t refuse.

Jen Davis, PhD, an Assistant Professor of Bioengineering and Pathology was one of the researchers at the backyard gathering. “That day was like a think tank of amazing ideas. Nobody felt like there were any barriers. We wanted to shoot for the moon. Everybody was all in. And we’ve been firing on all cylinders since then.”

Generous Funding for an Ambitious Project

The ISCRM team had the ambition, the expertise, and the facilities. If they could find the funding for their project, they would have everything they needed to begin. That happened sooner than any of them expected. Gree Real Estate, looking for visionary biomedical research efforts to support, agreed to seed the heart tube initiative with an initial investment of $100,000. Internal matches would bring the total infusion to $300,000 – a war chest that allowed the seven ISCRM faculty members to form the multi-disciplinary brain trust that would become known simply as The Gree Group.

Securing private funding for the “high-risk, high-reward” project was critical because it allowed the Gree Group to pursue a bold line of inquiry without amassing all of the preliminary data often required by federal agencies like the NIH. Pooling assets also enabled the Gree Group to recruit four trainees  – a.k.a., the Gree Scholars –  to work full-time on the intricate, interconnected first steps that are laying the foundation for long-term success.

“Financial support from Gree Real Estate is enabling us to pursue an ambitious goal,” says Dr. Chuck Murry, Director of the Institute for Stem Cell and Regenerative Medicine. “Our vision is to transform the treatment of heart disease by learning to regenerate heart tissue using pluripotent stem cells. This research is only possible because of the generous investment from Gree Real Estate.”

Biology and Engineering Join Forces

Image of a heart with red staining
Funding from Gree Real Estate is enabling experts in biology and engineering to study how the human heart develops – and how to grow heart tubes from stem cells.

Officially, the project began in November 2017 under the leadership of Nate Sniadecki, PhD, an Associate Professor of Mechanical Engineering and Bioengineering.  The members of the Gree Group – eight faculty, two postdocs, and two graduate students – are as eager to collaborate as they are to push the boundaries of medicine. While they meet once a month, the team does the vast majority of its research in three subgroups, each assigned to answer one of the central questions that underpin the challenge of engineering a heart tube. The subgroups are built around three particular specialties in the diverse of field of bioengineering: cell engineering, tissue fabrication, and biomaterials.

The diversity of skills and perspectives is a critical part of the mission. Gree Group member Cole DeForest, PhD, an Assistant Professor in Chemical Engineering and Bioengineering, explains the importance of the multidisciplinary approach. “When you’re trying to tackle problems of this scale, it’s impossible for one group to have all the expertise and know-how to be able to pull it off, so it’s essential – and really fun –  to be able to come together with our different knowledge sets.”

Nate Sniadecki also sees value in the blend of engineering and biology at the core of the project. “For me as a mechanical engineer, it’s fantastic to understand the developmental biology of the heart. From a basic science standpoint, it’s been useful to pick up the foundational knowledge. If you want to build something, you have to know how it works first. And, as engineers, we may ask questions that biologists don’t ask.”

Spying on Cells

The premise of the subgroup led by Sniadecki and Davis is deceptively simple: before scientists can grow a heart tube in a lab, they need to understand exactly how a heart tube grows in an embryo. Davis explains. “Nate and I are interested in the natural mechanisms that would make a heart tube during development. We’re doing whatever we can to learn how a cell would make a tube or even a whole heart in the embryo.”

Multicolored mosaic of magnified cells
To track how each heart cell contributes to the heart tubes, ISCRM researchers engineered human stem cells with genes that code for a variety of different colored fluorescent proteins so that each cell has a unique visual barcode.

To do that, Davis and Sniadecki needed a tool to observe in real time what cells do when they arrange themselves into a heart tube. And, because there are actually different types of cells involved, the cellular surveillance system had to allow them to understand which kinds of cells are doing which jobs – and what signals are giving these cells their marching orders. The task of designing this cellular spy cam belongs to Danny El-Nachef PhD, a postdoc recruited by the Gree Group for his microscopy skills.

Working out of ISCRM’s South Lake Union labs, El-Nachef genetically engineered human stem cells and installed genes that code for a variety of different colored fluorescent proteins. These proteins, which naturally exist in jellyfish, coral, and sea anemones, are the secret ingredients in so-called rainbow cells – essentially, cells with visual barcodes that allow the research team to track each stem cell under a microscope as they convert to heart cells. The goals are to study the properties of the cells that are most likely to be receptive to chemical signals in an engineered environment and to learn how to generate the diverse subtypes of heart cells needed to create a heart tube.

“We’re at a cool spot,” says El-Nachef, reflecting on the ability to deconstruct, and reconstruct, human biology. “If we can identify the factors that tell cells to become specific types of heart cells, we know we can make bioengineered tools that can mimic a heart tube.”

Signaling Cells to Loop and Fold

5 by 5 grid of squares with green and blue staining
Hydrogels embedded with cardiac growth cues. Gree Group researchers are using similar tools to track and manipulate how cardiac cells loop and fold as they become heart tubes.

While the cell engineering team is busy watching and tracking cell behavior, another subgroup, led by DeForest and Kelly Stevens PhD, an Assistant Professor in Bioengineering and Pathology, is focused on the signals that cause those behaviors. “Our challenge,” says DeForest, “is creating a synthetic hydrogel environment in which we can understand what signaling pathways are going to make the cells loop and fold – to become a heart tube.”

Essentially, the biomaterials subgroup is asking basic questions about the natural machinery that drives the development of the heart tube. The cells in the embryo have the genetic instructions to play their roles. For the Gree Group, the unknown is the extent to which the natural biological processes need to be jump started by putting them in the right shape and inducing them with the right signals.

According to DeForest, Ivan Batalov, PhD, a postdoctoral student and Gree Scholar, has played an instrumental role in this effort.  “Ivan has been pioneering techniques to create and modify hydrogels that can drive patterned cell growth similar to what occurs during heart tube looping.”  Meanwhile, in her own lab, Stevens is honing even more precise techniques to control how the cells arrange themselves and function.

DeForest is excited about the results. “The patterning is working incredibly well,” he says, referring to experiments underway in the hydrogel environments. “The cells are responding beautifully. The next challenge is to integrate the rainbow cells [engineered by El-Nachef] to visualize what’s happening and change the geometry of the material to mimic the actual shape of a heart tube.”

Studying Dimensions and Dynamics

Magnified image of a heart chamber with red and purple staining
Engineered vascularized cardiac chamber containing stem cell-derived cardiomyocytes, stromal cells, and endothelial cells

Shape is the business of the tissue fabrication subgroup, which is led by Deok-Ho Kim PhD and Ying Zheng PhD, both Associate Professors of Bioengineering and ISCRM faculty members. Two graduate students, Nisa Williams and Christian Mandrycky, are also members of this subgroup.

The cell engineering and biomaterials subgroups are studying the manner in which cells form heart tubes and learning to use light signals to coax those cells to essentially organize on demand. The tissue fabrication team is adding a third dimension to the project, literally.

“Our project is creating scaffolds that allow heart cells to function in a three-dimensional space,” says Williams, miming the process in a series of seamless arm and hand motions. “We pattern-stamp ridges and grooves onto sheer sheets of plastic and grow the cells right there. Then we fold the sheets into 3D shapes and cast them with the hydrogels that the biomaterials group are designing. It’s like tissue origami.”

These 3D scaffolds can be constructed to model the intricacy of heart tissue at any stage of cardiac development, giving researchers a lab-within-a-lab to study how hearts grow, how cardiac diseases begin, and even how potential drugs might help patients. The 3D models can also be used to measure biological functions, like heart beat rate and the velocity of blood flow. In a clinic, these vital indicators might help cardiologist treat a patient. For the Gree Group, these metrics are part of learning to engineer a heart tube.

Mandrycky is particularly interested in the dynamics of blood flow through the heart tube. “The tube really resembles a vessel,” he says. “The forces of flow are important to us because they begin when the heart tube closes. Replicating that shape lets us explore what effect changes in shape have on the cells that make up the tube. What happens if we apply pressure? How does it change the biology of those cells? Does alignment control development or do external forces drive alignment?  We’re gathering knowledge n0w so that we know what do with the tubes when we learn how to build them.”

Exposure to New Ideas

In the effort to engineer a heart tube, perhaps no group of people are gathering knowledge in more ways than the four Gree Scholars. In their ISCRM labs, Williams, Mandrycky, El-Nachef, and Batalov, are developing cutting-edge tools to visualize, direct, and construct the most basic components of a human heart. Collectively, they are the lifeblood of the project.

Side by Side photos of Nisa Williams and Christian Mandrycky
Nisa Williams (L) and Christian Mandrycky, both PhD students in ISCRM labs, are playing specialized roles on the heart tube project as members of the Gree Group

At the same time, the Gree Scholars are enjoying almost unheard-of access to a wide-range of perspectives from the ISCRM faculty members. Typically, a trainee is mentored by one or two senior scientists who guide their research and is critiqued by a review board in a conversation that is one-way by nature. Not so for the Gree Scholars, who now meet monthly with senior faculty members from a wide-range of disciplinary perspectives.

“It’s unlike anything that is available to a graduate student in any other way,” says Mandrycky. We have access to this really constructive group of people who are all experts in their field and they’re helping us to build out where our projects go. The opportunity to present to this group and see them be excited about our research is really unique.”

Williams echoes the assessment. “We’re definitely getting richer, personal feedback from experts than we would without this project. And I think they’re learning from us, too. For everyone in the room, it’s all about stirring creativity and exposure to new ideas.”

The contributions of the Gree Scholars may soon be documented in several scientific journals. One paper is under review, two others are being prepared for submission. Each manuscript aims to bring more attention to topics that are central to the Gree Group research, including rainbow cells and the proliferation of stem cell-derived heart cells.

Transforming Human Health

The work of the Gree Group takes place in the walls of research labs spread across the University of Washington. Over days, weeks, and months, faculty and trainees spend countless hours asking questions, testing ideas, and learning from each other as they attempt to turn a far-reaching idea hatched on a summer afternoon into applications that could improve the lives of billions of people.

“We’re motivated by why,” says Danny El-Nachef. “Why does this work the way it does? And we’re here to push the boundaries of technology today. At the beginning, we said, ‘this is impossible, but let’s try.’”

Of course the real story – the real why – is outside the walls of the lab.

In 2015, more than 17.3 million deaths were attributable to heart failure, a number that is expected to rise to more than 23.6 million by the year 2030. In the United States alone, one in every four deaths that occurs is due to heart disease. Like the U.S., China has similarly experienced a steady rise in heart disease, and with no signs of the trend abating.

The prospect of engineering a heart tube – and the peripheral benefits of knowledge gained on the journey – is a reason to believe that nothing is impossible.