To make their micro pumps, the researchers dissolved the polymer in dichloromethane, a solvent, and filled glass capillary tubes with the solution.

One of the ink’s solvents, dichloromethane, evaporated quickly to fix a printed layer in place.

It found only two — chloromethane and dichloromethane — and the scientists concluded that the chlorine compounds were contaminants from fluids used to clean the spacecraft.