Organs-on-a-chip hurtle toward the final frontier

Microfluidic devices lined with human cells are headed to the International Space Station in early May, part of an effort to understand why astronauts get sick more easily in orbit.

Dan Huh and Andrei Georgescu in the lab
Graduate student Andrei Georgescu and Assistant Professor Dan Huh in Huh’s lab. Adapting the organ-on-a-chip technology for a trip to the International Space Station presented Huh’s team with a number of engineering challenges. (Photo: Kevin Monko)

Throughout the 60-year history of the U.S. space program—from the Mercury capsules of the 1960s to today’s International Space Station—astronauts have been getting sick. Researchers know being in orbit seems to suppress their immune systems, creating a more fertile ground for infections to grow. But nobody really understands why.

Early on the morning of May 4, a SpaceX Falcon 9 rocket will launch a cargo mission to the ISS from Cape Canaveral Air Force Station. Along with fresh water, food, and other necessities for the crew, the craft will be carrying two experiments designed by Penn scientists that could help shed light on why bugs have bedeviled space travelers.

For more than a decade, Dan Huh, a professor in the School of Engineering and Applied Science, has been developing super-small devices that use living cells to stand in for larger organs. These organs-on-a-chip hold great promise for all kinds of research, from diagnosing disease to curing them. They’re also a way to test things, including drugs and cosmetics, in a way that mimics real life without relying on animal subjects.

We are thrilled with this rare opportunity to probe one of the potential major health issues in space using our organ-on-a-chip technology. Dan Huh

Last year, Huh and G. Scott Worthen, a professor of pediatrics at the Perelman School of Medicine and a neonatologist at Children’s Hospital of Philadelphia, got a $2 million grant to make the chips, then launch them into orbit, this year and again in 2021. The grant, from the National Center for Advancing Translational Sciences at the National Institutes of Health (NIH), NASA, and the Center for the Advancement of Science in Space, is part of a larger program to understand the physical and biological effects of space travel on humans.

“We are thrilled with this rare opportunity to probe one of the potential major health issues in space using our organ-on-a-chip technology,” Huh says. “It has been quite a journey to get to this point and we are all eager to see the successful launch of our devices.”

Orbiting infections

Solving the puzzle of illness in orbit is an important part of NASA’s long-term plan to send people well beyond the Moon, particularly to Mars. There are a number of concerns, including bone and muscle loss from extended periods of microgravity, DNA damage from radiation exposure, and even common motion sickness.  

Complete data on infections aren’t available, but NASA has reported that 15 of the 29 Apollo astronauts had bacterial or viral infections. Between 1989 and 1999, more than 26 space shuttle astronauts had infections.

Microscopy photo of Infected airway
This image from a scanning electron microscope shows the Pseudomonas aeruginosa bacteria in an airway. Part of the in-orbit experiment involves seeing how these bacteria react in lung tissue in microgravity.

For a short trip, an infection might not be a big deal. For ISS astronauts who have stayed in orbit for as long as a year or those assigned to future long-distance missions, understanding what’s happening is much more important.

The project’s Earth-bound impact will be significant, too. New insights gleaned from this study will deepen our understanding into the complex inner workings of immunity in the human body. This may also help scientists and drug companies develop more effective medical countermeasures for infectious and inflammatory diseases.

In general, organ chip devices can offer drug companies a way to test new treatments on human cells without risking harm to an actual person, saving money and improving accuracy in the process. They’re also an alternative to animal testing, which won Huh the Lush Prize last year. And they hold promise for the move toward personalized medicine. Huh’s lab also received a $1 million grant from the Cancer Research Institute to support work creating chips that mimic the interface of cancer and immune cells.

Ultimately, scientists want to start linking these organs-on-a-chip together, to be able to see how a drug, chemical, or other substance acts all over the human body. For the time being, the breakthroughs in the Huh lab are individual: Huh and his partners have developed models of the eye, lung, placenta, pancreas, cervix, and fat, opening the door to new studies on conditions ranging from preterm birth to diabetes.

“Research in my lab over the last six years or so has been driven towards the goal of advancing our ability to emulate the structural and functional complexity of human tissues and organs. As a result, there has been a lot of progress in developing novel devices and in vitro platforms for microfluidic cell culture and tissue engineering,” Huh says. “We are now trying to exploit these advanced systems to model and interrogate biological processes underlying complex human diseases. In collaboration with pharmaceutical companies, we are also beginning to use our organ-chip models for screening the efficacy and safety of therapeutic compounds.”

Illustration of Huh's lung-on-a-chip in space
This illustration of the lung-on-a-chip shows the lung cells, complete with cilia, on the upper layer and the capillary cells, to move blood, on the lower layer.

Launch pressure

Huh and his team have created two separate experiments for this first launch. The first essentially mimics an infection inside a human airway, to see what happens to the bacteria, and the surrounding cells, in orbit.

Huh’s BIOLines lab created the actual chips. Graduate students Andrei Georgescu and Jeongyun Seo work with Huh on the project, while Worthen and postdoc Dipasri Konar handle the lung immunology questions.

The lung chip is made of a polymer, and a permeable membrane is the platform for the human cells. For the lung-on-a-chip, one side of the membrane is coated with lung cells, to process the air, and capillary cells on the other, to provide the blood flow. The membrane is stretched and released to provide the bellows-like effect of real lungs.

Vascularization transition
Huh and his team have created real blood vessels that can interact with the human bone marrow cells, to let them track the movement of neutrophils in response to the bacterial infection.

The bone marrow chip contains whole human bone marrow cells, and blood vessels that have been created to mimic what’s in the body. Organic blood vessels, Georgescu says, have signature crimps that keep them together, sort of like the edges of a pie crust. Looking at the cultured vessels through a scanning electron microscope, he says, you can see those crimps.

“We’re making real vessels, not just what a vessel should look like,” he says.

The bone marrow test aims to observe how the marrow the source of the white blood cells the body sends out as the first line of defense against infection behaves in space. The team is looking for the speed of the activation and movement of neutrophils, the most abundant type of white blood cells, in response to the same bacteria, Pseudomonas aeruginosa, that is used to infect the airway cells.

The results will help researchers better understand what’s happening. Do the bacteria multiply faster in the airway? Do the neutrophils respond more slowly? Or is there something else going on?

Microscopy photo of blood vessel crimping
This view of the vessel lumen in an engineered blood vessel, captured with a scanning electron microscope, shows the signature crimps that you’d see in organic vessels. The crimps help keep the vessels sealed against leakage.

During the two weeks that the experiments are active, control experiments will be unfolding back on Earth. Then, once the ISS chips come back a month later, researchers can see what, if anything, happened differently to the two groups. Analyzing the results will take months.

“We want to see, for each of these tissues, do they respond differently to these bacteria? It could be at Zero-G there’s an effect on the lung cells, or on the bone marrow, or both,” Georgescu says. “We’re looking at the two separately, giving the bone marrow a cocktail of what it would see with an infection, and giving the airway a real bacterial infection, so we can see which responses behave differently in space.

“Then, we’ll connect the two together, so we can look at the process and see what’s happening.”

That second combined experiment will launch in 2021, and also feature a control on Earth.

Breaking new ground

Huh has been working on these projects for many years, since his postdoctoral work at Harvard’s Wyss Institute for Biologically Inspired Engineering, where organs-on-chips were first created. Since coming to Penn in 2013, he has continued to push the work forward, developing other organs and refining the lung-on-a-chip he and colleagues presented in 2010.

Animation of robotic hole punch
Among the inventions the team had to engineer: This robotic hole puncher, which makes holes with smoother edges as well as speeding the process of punching the polymer surface.

As new developments are made, the lab is also working on scaling up the production of the existing chips, to make them more viable for everyday use. For example, the polymer plates that are the backbone of the chips need lots of holes punched in them so that the microfluids containing the cells can be injected.

The automated hole punch developed in the lab has not just made the process faster, but more accurate, since the hole is cleaner and more uniform.

The ISS experiment created a number of additional engineering challenges, Georgescu says, that have kept the team busy even as the launch grows near. Huh and Worthen brought in two microgravity research companies, SpacePharma and Space Tango, to help address some of them.

“The space project has kind of forced us to develop solutions on the technical side that otherwise we wouldn’t have needed to do,” Georgescu says.

Animation of syringe pump injecting an organ on a chip
This special syringe pump was another innovation needed for the space mission. It will also allow the organs-on-a-chip to be built more quickly back on Earth.

One major obstacle was figuring out how to keep the experiments going, without human intervention, during the two active weeks in orbit. The team built special syringe pumps to help them keep the chips fed.

Another challenge was adapting the process of growing the chips to the timetable of the launch, docking with the ISS, and other mission logistics.

The chips must be pre-grown, and “seeded” with cells two weeks in advance to give the cells time to grow. The final versions are ready four days before the launch. But because launches are notorious for delays, the team has been working furiously.

“We have such a strict timeline,” Georgescu says. “We’ve been making replicas of these over and over in these weeks before the launch, just in case today’s chips are the ones to go up.”

Dan Huh is the Wilf Family Term Assistant Professor of Bioengineering in the School of Engineering and Applied Science at the University of Pennsylvania.

G. Scott Worthen is Physician-Scientist in Neonatology at Children's Hospital of Philadelphia and a Professor of Pediatrics at the Perelman School of Medicine.

This research was supported by National Institutes of Health grant 1UG3TR002198.

Images courtesy of BIOLines Laboratory.

Blood vessels
Engineered blood vessels are shown here in purple with cell nuclei, in blue dye.