It sounds like something out of a Terminator movie. Chemical engineers at the University of Michigan have developed a plastic that instantly heals itself when it’s cracked by a bullet or other projectile.
“We were interested in using action to start a chemical reaction,” says Scott Zavada, a PhD candidate who worked on the project.
Zavada and his lab mates had been working on self-healing materials for medical uses—surgical adhesives that could be used instead of stitches, for instance. But when they heard that a team at NASA's Langley Research Center was working on similar technology to try to quickly heal holes in space suits and outer space habitats, they switched gears. The University of Michigan engineers joined forces with NASA to create a material that solidifies once it is exposed to the atmosphere. “Once we started working with NASA, we decided we might be able to use the action of oxygen leaking to drive that reaction,” Zavada says.
Their goal was to create a material that could heal itself almost instantaneously, because, in space, a rip in a space suit or breach of a space station wall can be deadly.
Zavada and his advisor, Tim Scott, came up with a solution. They sandwiched tributylborane, a chemical that quickly hardens when it’s exposed to oxygen, between two layers of plastic. When one or both of the plastic sheets was punctured, the tributylborane immediately started hardening, covering the hole.
To those who have been reminding the engineers that there’s no oxygen in space, Zavada says, “We’re relying on the oxygen that’s coming out through the hole that breaks the surface. Any place that there’s a human residing, there will be oxygen.”
Scott says there wasn’t any great breakthrough moment; the researchers brainstormed for a while, and the first thing they settled on ended up working well. To test the healing properties, the engineers did the most obvious thing they could think of. They took the material to the gun range and shot it up.
The challenge has been in making sure there’s no oxygen at all between the plastic sheets when they’re put together. “We have a very specific lab here for degassing, so it’s kind of hard to go to a different lab and recreate those conditions,” Zavada says. “But it’s very translatable as long as you can dissolve the oxygen.”
Self-healing materials aren’t new. There is actually a fairly wide range of polymers that can heal themselves, which can be used for thing ranging from cracked phone screens to holes in rain jackets. But the one that Zavada and Scott developed is by far the fastest. They say, depending on how big the puncture is and how quickly the oxygen dissolves, it heals in a matter of seconds. “Ours is most suitable for things that need to be healed very quickly,” Scott says, “not, for instance, a scratch in paint where the timeframe doesn’t matter.”
Next month, the team is taking the material to NASA’s Glenn Research Center in Cleveland to test it in a controlled environment that mimics space. All the tests they’ve done so far have been at atmospheric pressure, so they want to see how it holds up in zero gravity. The researchers hope to be done with testing by the end of the year. From there, they'll hand the plastic over to NASA to see how it can be incorporated into space suits and habitats.