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How do you make a human heart? Maybe in zero gravity.

Cardiac tissue printed in space could be a lifesaving breakthrough for transplant patients — if it can survive the return to Earth.

By Tony Rehagen

In a parking lot at Johnson Space Center in Houston, in the back of a rented Suburban, Gene Boland was about to get the answer he’d awaited for months. It was Jan. 9, and Boland and senior scientist Carlos Chang had flown down from Louisville to pick up three samples from an International Space Station experiment, conducted with a bio-printer they had helped design. Its product: synthetic human heart tissue, created in space.

At the Johnson Space Center’s cold stowage unit, the scientists had picked up three plastic boxes, each about the size of a gaming console. Called culturing cassettes, they each held one tissue sample. Boland and Chang carefully brought the cassettes to the SUV, whose interior was covered in surgical drapes. Inside, they donned protective surgical clothes and sleeves, held the first cassette in their latex-gloved hands, and opened it to see if their creations had survived the trip back into Earth’s atmosphere. They were about to see whether they and their company, Techshot, had changed medical science forever.

Since the advent of 3D printing, physicians and scientists have dreamed of fabricating human body parts for transplant. And, to an extent, they’ve succeeded. Today, people are walking around with 3D-printed prosthetics, including fully functional hands. In the last few years, researchers have also had breakthroughs using “inks” made from stem cells and naturally derived polymers. They’ve printed cartilage, bones, and even skin and smooth muscle, some of which is being tested in animals in preparation for human trials.

The ability to print a human heart would mean, for many patients, the difference between life and death. On any given day, 3,000 to 4,000 people are on the waiting list for a heart transplant. More than one in four of them die waiting.

But bio-printing an organ as complex as a heart is a trickier proposition. The human heart is comprised of several different kinds of cells — ventricular, atrial, various muscles. It must be connected with blood vessels to provide oxygen flow and enable the organ to pump and grow. Researchers have tried to reproduce cardiac tissue with 3D printers on Earth, printing it layer upon layer. But this cocktail of fluid biomaterials has proven too heavy to maintain structural integrity. Essentially, it melts into a puddle of goo.

That’s the problem Techshot hopes to solve. The company — which operates out of a squat two-story headquarters in Greenville, Indiana, near the border with Kentucky — specializes in developing technology for aerospace, defense, and medical industries by running experiments in microgravity, the near-zero gravity of space. They hope to print cardiac tissue in space that will withstand Earth’s gravity and provide lifesaving transplants for a long list of people in need.

Last summer, in Techshot’s Payload Operations Control Center, scientists worked at night, on the same schedule as the astronauts aboard the International Space Station, their clocks set to Greenwich Mean Time. Their work stations were cluttered with coffee, doughnuts, and White Castle hamburgers.

The team in Indiana talked to its partners in space, including astronaut-engineers Christina Koch and Jessica Meir, who conducted the first all-female spacewalk in October, as well as astronauts Nick Hague and Drew Morgan.

NASA astronaut Christina Koch, Expedition 60 flight engineer, works with the BioFabrication Facility. Photo by NASA

Techshot staffers talked the astronauts through the steps of operating the BioFabrication Facility — a machine known inside the company as the BFF. A 3D printer about as big as a mini-fridge, the BFF essentially squirts bio-inks made with adult stem cells and a proprietary cocktail of proteins and tissue-growth factors. The printer forms layers that can be measured in microns to reproduce human tissue in the microgravity of space.

The printed sample was a neonatal heart, the size of an adult pinky finger’s tip. For 29 seconds of freefall, the synthetic heart maintained its shape.

The idea is the brainchild of Boland, chief scientist at Techshot. Before joining the company in 2013, Boland had compiled a 20-year career in biomedical engineering. As head of regenerative medicine at the University of Louisville, he’d engineered prosthetic heart valves. He had tried 3D printing and seen how difficult it was to get cells to maintain their structure under their own weight.

But then, his laboratories were earthbound. His new employer’s experience with microgravity suggested an alternative solution. At Techshot, Boland saw dozens of experiments and tools that used the zero-G of space. One stood out: a piece of equipment that grew cardiac cells for injection into patients’ heart muscles following a heart attack. 

“The apple fell on my head when I started seeing how materials react in microgravity,” Boland says. “Because fluids behave differently in microgravity — no sedimentation, no flowing — things tend to stay where you put them.”

For decades, Techshot had developed tech for other companies, universities, and agencies like NASA. But Boland’s bosses decided Techshot should develop a zero-G 3D bioprinter on its own. If the company owned the printer, clients could hire it to create cartilage, bone, tissue, or just about anything. And with Boland and his team’s experience in cardiac bioengineering, Techshot had the necessary in-house expertise.

Techshot found an enthusiastic partner in an Orlando, Florida-based bioprinter manufacturer called nScrypt. But that was it. At first, no other outside investors, no academics, and not even the researchers at NASA were ready to buy in. They saw it as “crazy science fiction stuff,” Boland says.

Still, Techshot moved forward, building a prototype 3D printer and flight unit for around $7 million. In 2016, they tested it on a parabolic-flight aircraft, a jet that achieves near-weightlessness for a brief period. (Used to train astronauts, it’s been nicknamed “the vomit comet” by weaker-stomached passengers.) During the flight, they created a printed sample, made with adult human stem cells and common bio-ink: a dual-ventricle, neonatal heart, the size of an adult pinky finger’s tip.

For those 29 seconds of freefall, the synthetic heart not only maintained its shape, but, in a development that shocked even Boland, the layers being printed were actually fusing together into a whole. “We were printing solids,” says Boland, “with no internal boundaries.” That breakthrough was enough to get NASA on board.

It took years to downsize the printer to a suitable size for a space-station payload and develop the thin “inks.” Comprised of nutrients, proteins, and decellularized adult human tissue, they form tissue thanks to processes that resemble embryo genesis and wound healing.

In July 2019, the BioFabrication Facility was launched to the space station from Cape Canaveral, Florida, aboard the un-crewed supply capsule SpaceX CRS-18.

Many in the medical and bioengineering community are watching closely. They have high hopes for this technology, but they understand the challenges ahead.

“The tech is there,” says Danilo Tagle, associate director for special initiatives for the National Institutes of Health, who studies the effects of microgravity on cell behavior. “The opportunity is here to almost spray into form a 3D organoid” — an organ-like structure — “without the constraint of gravity.”

But creating heart tissue in space is only the first step. The next challenge is getting complex biological material printed in microgravity to survive on the Earth’s surface. “How do you strengthen the connective tissue so, when you bring it back, it will maintain form?” says Tagle. “The cells and tissues are primarily sourced from Earth and can be brought up. Now you’re just trying to see how those constructs withstand the descent.”

That’s the problem staring down Boland and company right now. A test of the BioFabrication Facility aboard the space station last summer was a partial success. The astronaut printed all the components of cardiac tissue — nerve cells, vascular cells, and muscle. It all flowed together well in microgravity. But the initial calibration of the machine took weeks, leaving less than a week for the material to gestate before it returned to Earth in supply capsule CRS-18, which landed in the Pacific Ocean in August. Plus, the inks they used were as viscous and thin as possible, making them more susceptible to melting under Earth’s gravity. What came back was little more than a puddle.

“Our first attempt was really a swing for the fences to find out how thin can we can go, how fast can we go,” says Boland. “We probably got a little bit overzealous.”

For the second test on the space station, Boland and his team allotted more than a month for the slightly thicker materials to take form. That’s what returned to Earth on January 7 aboard SpaceX CRS-19, splashing down in the Pacific Ocean with the answer to Boland’s question.

In the Johnson Center parking lot, Boland and Chang lifted the lids off each of the three cassettes. Through the cassettes’ viewing windows, the scientists saw that the tissue samples had disintegrated somewhere between space and splashdown. Once again, their tissue had turned to goo — and, momentarily, so had Boland’s dreams.

But Boland and Techshot are far from deterred. Further evaluation of the samples back in Indiana indicated that the problem was not in the tissue’s construction, but in its subsequent nourishment. Boland believes that air bubbles, which also behave differently in zero-G, clogged one of the pumps feeding the printed tissue. He and his team already have a new pump, ready to ship back to the ISS. But the next SpaceX flight that can deliver it doesn’t launch until January 2021.

If a bioprinting experiment is ultimately successful, the next question will be how to scale up the efforts — from a sheet of cardiac muscle to a functioning, fist-sized human heart.

“Technology has a great way of leapfrogging quickly,” says Valluvan Jeevanandam, a cardiac surgeon, transplant specialist, and professor at University of Chicago Medicine. “But there are real hurdles that need to be crossed. How are you going to put in blood vessels? How will nerves react in sequence? How are you going to create a valve? How are you going to electro-charge it?”

Boland and Techshot aim to find out. Their current timeline calls for the first phase of testing prints to last two years. During that time, they’ll gradually increase the thickness of the printed tissues. In Phase 2, they’ll create patches of cardiac tissue that could be grafted onto a heart and evaluate them on Earth under microscopes, and perhaps in animals. That process could last through 2024. Only then will they attempt to manufacture a full-scale organ in space.

Researchers and scientists believe it might well be worth the wait. In addition to its impact here on Earth, this technology could open up other possibilities, says Tagle, including 3D-printed meats and vegetables. And Boland and many of his Techshot colleagues, who dream bigger than the Earth, hope that a BFF-like printer would be launched aboard the first deep-space transport. They hope it could produce nearly any biological material an interplanetary traveler might need — including tissue for transplants — on a journey to Mars or beyond.

“A career-long goal of mine, and now Techshot’s, is to address the global organ shortage,” says Boland. “But bioprinting could be the only means of organ or tissue replacement during exploration and, eventually, outposts. That’s of interest to NASA and everyone with dreams of living in the stars.”

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Tony Rehagen is a writer based in St. Louis.


Top photo of astronaut Jessica Meir by NASA.


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