Astronauts are growing the beginnings of new organs on board the International Space Station.

The experiment is an attempt to grow human tissue by sending adult human stem cells into space, and allowing them to grow in space.

Eventually, it is hoped, the stem cells will develop into bone, cartilage and other organs. If that is successful, the discoveries could be used to try and grow organs for transplant, the scientists involved say.

The experiment uses “weightlessness as a tool”, according to Cara Thiel, one of the two researchers from the University of Zurich who are conducting the research. The lack of gravity on board the International Space Station will be used to encourage the stem cells to grow into tissue in three dimensions, rather than the single-layer structures that form on Earth.

It is being conducted by the astronauts on board the International Space Station using a “mobile mini-laboratory” that was sent on a SpaceX rocket last week. The experiment will last for a month, during which scientists will watch to see how the stem cells grow.

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If it is successful, they hope to switch from a small laboratory to bigger production. From there, they could use the process to generate tissue for transplants by taking cells from patients, or generating organ-like material that could be used to test drugs, either ensuring that it works for a specific patients or reducing the number of animals used in experiments.

On Earth, tissue grows in “monolayer” cultures: generating flat, 2D tissue. But investigations both in space and Earth suggest that in microgravity, “cells exhibit spatially unrestricted growth and assemble into complex 3D aggregates”, said Oliver Ullrich, who is also leading the research.

Previous research has involved simulated ad real experiments, mostly using tumour cells, and placing real human stem cells into microgravity simulators. But for the next stage of the research “there is no alternative to the ISS”, he says, because 3D tissue formation of this kind requires several days or even weeks in microgravity.

After the month-long experiment, the scientists will get the samples back and expect to see successful formation of ”organoids” – smaller, more simple versions of organs – inside the test tubes. “The test tubes were launched with stem cells and are expected to return to Earth with organ-like tissue structures inside,” said Professor Ullrich.