According to multiple studies (see here, here, and here), a whole range of microorganisms, from bacteria (some dangerous) to fungi, have been found prospering on ISS.
The photo to the right shows a typical example of fungi growing on one of ISS’s older surfaces.
A European Space Agency (ESA) project is attempting to developing new coatings that will not only protect surfaces but act to clean them as well.
“With astronauts’ immune systems suppressed by microgravity, the microbial populations of future long-duration space missions will need to be controlled rigorously,” explains ESA material engineer Malgorzata Holynska. “So ESA’s Materials’ Physics and Chemistry Section is collaborating with Istituto Italiano di Tecnologia, IIT, to study antimicrobial materials that could be added to internal cabin surfaces.”
The IIT team has begun work on titanium oxide, also known as ‘titania’, used for example in self-cleaning glass down here on Earth, as well as in hygienic surfaces. When titanium oxide is exposed to ultraviolet light, it breaks down water vapour in the air into ‘free oxygen radicals’, which eat away whatever is on the surface, including bacterial membranes. “Bacteria gets inactivated by the oxidative stress generated by these radicals,” says Mirko Prato of IIT. “This is an advantage because all the microorganisms are affected without exception, so there is no chance that we increase bacterial resistance in the same way as some antibacterial materials.”
The application however is not as simple as painting the surface. Right now they wish to keep this coating as thin as possible (“50 to 100 nanometres, millionths of a millimetre”) so that it could even be applied to clothing, which requires using complex techniques similar to those used to make semi-conductors.
Though hand cleaning would likely be much simpler and cheaper, there are issues. First, it isn’t as easy to scrub a surface by hand in weightlessness. Second, in a closed environment like ISS cleaning materials pose a greater hazard to both the occupants and the equipment. Better if the surfaces of equipment and clothing are designed to stay clean, on their own.
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