New Delhi: Several microorganisms reside in space, and can pose a serious threat to the health of astronauts who live and work in Earth orbit. Now, a project led by the European Space Agency (ESA) is developing microbe-killing coatings suitable for use within spacecraft cabins to help combat such invisible stowaways.
A microbial survey of the International Space Station (ISS) was conducted, which revealed that the orbital outpost has dozens of different bacteria and fungi species, including harmful pathogens such as Staphylococcus aureus, that is known to cause skin and respiratory infections as well as food poisoning.
The microbes can not only make the astronauts sick, but also the spacecraft. Bacteria and fungi produce 'biofilms' similar to the plaque on one's teeth. These biofilms can in turn tarnish and eat away metal and glass as well plastic and rubber, the ESA said on its website.
The ISS's predecessor, the Mir space station, faced this problem in its latter days, when microbial colonies were observed to grow on parts of spacesuits, cable insulation, and even the seals of windows.
Why Should Microbial Populations On ISS Be Controlled?
In an ESA statement, Malgorzata Holynska, a material engineer working with the space agency, said that with astronauts' immune systems suppressed by microgravity, the microbial populations of future long-duration space missions will need to be controlled rigorously. 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, he further said.
Why Is Titanium Oxide Used To Make Self-Cleaning Surfaces?
According to the ESA, the IIT team has begun work on titanium oxide, also known as 'titania', used in self-cleaning glass down here on Earth, as well as in hygienic surfaces. When exposed to Ultraviolet light, titanium oxide breaks down water vapour in the air into 'free oxygen radicals'. These eat away whatever is on the surface, including bacterial membranes.
The oxidative stress generated by these radicals inactivated the bacteria, according to Mirko Prato of IIT. He also said that this is an advantage because all the microorganisms are affected without exception, because of which there is no chance bacterial resistance is increased in the same way as some antibacterial materials.
The team chose titanium oxide after studying previous research on antimicrobial coatings for hospitals. The researchers are tweaking the recipe to make the compound in order to increase its sensitivity to the visible portion of the light spectrum.
Why Is Silver Not Preferred To Make Antimicrobial Coatings For Spacecraft?
Malgorzata said antimicrobial coatings on Earth often make use of silver, but the researchers want to do without silver in space. The issue is that in the confined environment of a spacecraft, prolonged exposure to silver could have negative health effects for astronauts, he added.
Malgorzata also said the silver may cause a heavy metal buildup in the water on the space station, and the soluble silver can cause skin and eye irritation.
How Is Titanium Oxide A Good Alternative To Silver?
Fabio Di Fonzo of IIT explained that one of the attractions of titanium oxide as an alternative is its apparent long-term stability. He added that the researchers will be performing artificial ageing of coatings to see how they evolve over time. Part of the project will be to see what are the photo-degradation products going back into the cabin atmosphere once the bacteria are oxidised, because the scientists do not want the end products to be more toxic than the microbes themselves.
The scientists created a successful titanium oxide coating of a variety of candidate surfaces such as glass, silicon wafer, aluminium foil, and even clean-room grade paper tissue. There are several methods which can help put the coatings in place. These include 'physical vapour deposition' and 'atomic layer deposition'. The processes involve the gradual laying down of thin films by exposure to gaseous chemicals, which are techniques more traditionally employed for fabricating semiconductor devices.
Mirko said the researchers aim to keep the antimicrobial layer as thin as possible, so as to not alter the mechanical properties of underlying materials too much, not to stop fabrics from bending and so on. The scientists are targeting thicknesses of 50 to 100 nanometres, millionths of a millimetre.