Two projects aiming to engineer muscle fibres and liver tissue on board the International Space Station (ISS) could help develop innovative biomedical treatments, and perhaps one day see full human organs grown in space.
Researchers have studied the effects of microgravity on different types of cells for decades, but this would be the first attempts to cultivate large volumes of human tissue in space.
The first study will look at muscle grown in a bioreactor鈥攁 nutrient-rich chamber鈥攊n order to assess new drugs for muscle loss, a natural ageing process that starts to occur in physically inactive people in their 30s and can worsen over time.
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鈥淭he degree of muscle loss can be so significant that it creates a risk of frailty and can lead to poor health outcomes,鈥� says Ngan Huang of Stanford University in California.
While diet and exercise can alleviate some of these effects, doctors have long sought drugs to complement such practices.
Microgravity muscle loss
People who spend extended periods in microgravity also experience muscle loss, which is why astronauts must exercise rigorously while in space. Huang and her colleagues wanted to know if spaceflight could mimic muscle wasting on much shorter timescales.
Next year, the team intends to launch their experiment to the ISS and assess whether microgravity mimics an accelerated version of muscle loss. If so, they hope to test different drug treatments in space that might show promise for the disease.
The work might not only be beneficial to humans on Earth, but astronauts who suffer from muscle loss on long expeditions as well.
The second experiment will attempt to grow a three-dimensional structure made from functional liver tissue. Biomedical engineers have produced thin bits of tissue such as cartilage or skin in the past, but a complex organ like the liver has proven challenging.
Part of the problem is that organs inside the body develop in a soft and buoyant environment, whereas artificial scaffolding for tissue engineering tend to be made of hard plastic and cells settle to the bottom of a container under the influence of gravity.
Spinning organs
Liver tissue grown in a rotating bioreactor, mimicking the effects of microgravity, have already shown some promise. These cells are able to metabolise more drugs than those engineered in static containers.
But as cell clusters grow, rotating bioreactors need to spin faster in order to keep them suspended and eventually the cylinder begins turning so quickly that the tissue is pinned against the walls.
Microgravity might more easily mimic the natural environment where organs develop. In the next few years, surgeon scientist Tammy Chang of the University of California, San Francisco, and her colleagues hope to send different stem cells that can give rise to the various tissues and blood vessels of the liver to the ISS. A microscope will film the cells as they grow inside a bioreactor and the resulting tissue will be brought back to Earth.
Chang says the eventual goal is to transplant some of the tissue into a rat and see if it functions properly, potentially opening up a new way to produce livers for patients on organ donor lists.
鈥淚magine if we show that we can generate life-saving tissues in orbit, and there鈥檚 no other way to do that,鈥� she says, adding that it might spur rocket technology to access low-Earth orbit more cheaply.
Testing tissue growth in reduced gravity could reveal some unknowns, says bioengineer Jordan Miller of Rice University in Houston, Texas, who is not involved in either project.
鈥淚f we can validate that microgravity has a positive effect, maybe some of the biochemical pathways activated in a microgravity setting could be identified and those could be directly stimulated here on the ground,鈥� he says.
