Joshua Gershlak, PhD
What if doctors could one day print living tissue the way we print documents—on demand, precisely shaped and tailored to each patient?
Once the stuff of science fiction, the emerging field of 3D bioprinting has advanced rapidly, with researchers at Mass General Brigham (MGB) now using the technology to create living heart tissues that could transform how we understand disease, test new therapies and repair the human heart.
For the past few years, postdoctoral researcher Joshua Gershlak, PhD, and his colleagues have been working on this ambitious goal.
“My background is in biomedical engineering, in particular tissue engineering,” says Gershlak, who recently transitioned out of his research role at MGB but is continuing his work at the Harvard School for Engineering. “Throughout my postdoc, I've been working on two main projects that are largely focused on the heart and engineering tissue in different ways for it.”
Creating a Heart from "Living Ink"
While the first project—an organoid heart-in-a-dish—helped the team answer some questions about heart function and cardiac disease, there were limitations to what this model could replicate in the lab.
Thus, they started to wonder if they could use 3D bioprinting technology to create an entire living four-chamber heart.
Bioprinting is a way of using “living ink” to build human tissue, layer by layer. Think of it like a regular 3D printer, but instead of printing plastic or metal, it prints living cells, often mixed with supportive materials that help the cells survive and grow.
The goal is to create real biological tissue, such as skin, blood vessels or small pieces of organs.
This is a mini-heart that started as a tube and then underwent the same mechanical motion that the heart goes through in utero to form a multi-chambered organ.
Pushing the Limits of 3D Printing
This bioprinting project, known as SABER, sought to push 3D tissue engineering into new, living areas of cardiac medicine.
In simple terms, the bioprinting process begins with scientists collecting living cells, often from a patient or donated tissue. These cells are then mixed into a gel-like substance called bioink.
Using a specialized printer, the bioink is deposited layer by layer according to a digital design—much like carefully icing a layered cake.
After printing, the cells are maintained in conditions that allow them to grow, connect, and function like real tissue.
Just like in many 3D printing processes, Gershlak and colleagues decided to use a suspension method of printing, where the living cells they print are placed into a gel-like supportive substance that allows the design to form in three dimensions.
“If you're looking at it from an engineer's perspective like I am, [the heart is] an organ that is mechanically active, it's robust, it's moving, it's 60 beats per minute."
— Joshua Gershlak, PhD
However, this is not as easy as just hitting print. One of the main challenges of using 3D bioprinting is keeping the tissue alive during the printing process.
What makes SABER unique is that it allows researchers to print new cells and then pause the process to provide nutrients and support to the existing cells, thus extending the lifespan of the bioprinted cells to allow for building larger, more complex models.
“If we wanted to print a whole human heart right now, it would take about four to five days of continuous printing (without stopping to provide support to the existing cells). However, this is too long to keep tissue alive, especially for the heart, which is highly metabolically active,” says Gershlak.
“The idea of SABER is instead of that four-to five-day period, we extend it to 20 days or so, but we are able to flow nutrients into the tissue in between printing, so we would end up with a living tissue or organ.”
Challenges and Hurdles to Overcome
A portion of the heart that was bioprinted over the course of four consecutive days, where a small piece of the heart was printed each day prior to being incubated overnight.
While the promise of this work is substantial, Gershlak is quick to note that translating bioprinted heart tissue into patient care will take time.
“There are a lot of engineering control issues in this process,” he explains. “When you are bioprinting over multiple days, there are lots of ways for infections to occur, and there are a lot of issues with perfectly lining up the tissues.”
Despite these challenges, Gershlak remains motivated by both the complexity of the heart and the potential impact of the work.
For him, the heart represents an ideal and endlessly fascinating engineering problem.
“If you're looking at it from an engineer's perspective like I am, it’s an organ that is mechanically active, it's robust, it's moving, it's 60 beats per minute. And then it's causing fluid flow that is all completely timed and precisely controlled by electrical activity.”
“So, the convergence of all these things makes it a lot of fun to dream about and try to play with. There’s a [clinical] need for it too, so my interest kind of grew from the intersection of all of that.”
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