Scientists report that after exposure in space aboard the International Space Station, a new type of surface treatment dramatically reduced biofilm growth. Biofilms are mats of microbial or fungal growth that can clog hoses or filters in water treatment systems, or cause disease in humans.
In the experiment, the researchers examined a variety of surfaces treated in different ways and exposed them to bacteria called Pseudomonas aeruginosaIt is an opportunistic pathogen that can cause infection in humans, especially in hospitals. The surfaces were incubated for three days aboard the space station, starting in 2019. The results show that the textured surfaces impregnated with a lubricant were highly successful in preventing the growth of biofilms during their extended exposure in space. The results are described in a paper in the journal Microgravity natureby Samantha McBride Ph.D20 and Kripa Varanasi of the Massachusetts Institute of Technology, Pamela Flores and Luis Zea of the University of Colorado, and Jonathan Galakza of the NASA Ames Research Center.
The blockages in the hoses of the water recovery system aboard the International Space Station were sometimes so severe, the hoses had to be returned to Earth to be cleaned and replenished. Although it is not known whether biofilms directly contributed to astronauts’ illnesses, biofilms on Earth are associated with 65 percent of microbial infections and 80 percent of chronic infections, the researchers say.
One approach to preventing biofilms is to use surfaces coated with certain minerals or oxides that kill microbes, but this approach can fail when a layer of dead microbes builds up on the surface and allows biofilms to form over it. But that wasn’t the case with the liquid-filled surface that performed so well in ISS experiments: instead of killing microbes, it kept them from sticking to the surface in the first place.
The specific surface used was made of silicon that had been etched to produce a nano-pillar forest. This spiky surface is then infused with silicone oil, which is drawn into the tissue and held in place by capillary action, leaving a very smooth and slippery surface that greatly reduces adhesion of microbes and prevents them from forming a biofilm.
Identical experiments were performed on Earth as well as on the space station to determine the variations produced by the orbit’s microgravity environment. To the researchers’ surprise, the liquid-filled surface performed better in space than on Earth at preventing microbes from sticking together.
On past and present space stations, including the Soviet Union’s Mir, Salyut 6, and Salyut 7 stations, as well as the International Space Station, “they’ve seen these biofilms compromise a variety of instruments or equipment, including spacesuits, says Varanasi, a professor of mechanical engineering and founder of a company called LiquiGlide, which makes liquid-impregnated surfaces for containers to help contents slide out.
Previous on-the-ground tests have shown that these treated surfaces can significantly reduce biofilm adhesion. When the samples were retrieved from the space station and tested, “we found that these surfaces are very good at preventing the formation of biofilms on the space station as well,” says Varanasi. This is important because previous research has found that microgravity can have a significant impact on biofilm shapes, attachment behavior, and gene expression, according to McBride. Thus, strategies that work well on Earth for biofilm thinning may not necessarily be applicable in microgravity situations.
The team says that preventing biofilms will be especially important for future, long-duration missions, such as to the Moon or Mars, where the option to quickly return contaminated equipment or sick astronauts to Earth would not be available. If further testing confirms its long-term stability and successful biofilm prevention, coatings based on the fluid-treated surface concept could be applied to a variety of critical components known to be susceptible to biofilm contamination, such as water treatment hoses and filters, or to parts that are in contact Close contact with astronauts, such as gloves or food preparation surfaces.
In terrestrial samples, biofilm formation decreased by about 74%, while samples from the space station showed a decrease of about 86%, says Flores, who has done a lot of testing on exposed samples from the International Space Station. “The results we got were surprising,” she says, because previous tests by others had shown that biofilm formation was actually greater in space than on Earth. “We found the opposite in these samples,” she says.
And while the tests used a specific, well-studied type of Gram-negative bacteria, she says, the results should apply to any Gram-negative bacteria, and likely to apply to Gram-positive bacteria as well. They found that areas of the surface where no bacterial growth had occurred were covered with a thin layer of nucleic acids, which have a slight negative electric charge that may have helped prevent microbes from sticking together. Flores says that both Gram-positive and Gram-negative bacteria have a slight negative charge, which could kick them off this negatively charged surface.
Other types of anti-fouling surfaces, Varanasi says, “mostly have a biocidal property, which usually only works with the first layer of cells because after those cells die they can form deposits, and microbes can grow on top of them. So, that’s usually the problem.” very difficult.” But with a surface impregnated with liquid, where mostly only the liquid itself is exposed, there are very few imperfections or spots where bacteria can find a foothold, he says.
Although the test material has been on the space station for over a year, the actual tests were only conducted over three days because they require the active participation of astronauts whose schedules are always busy. But one of the team’s recommendations, based on these preliminary findings, is that long-term testing should be carried out in a future mission. In these first tests, the results after the third day looked the same as after the first and second days, says Flores. “We don’t know how long it will be able to maintain this performance, so we definitely recommend a longer incubation period and also, if possible, continuous analysis, not just endpoints.”
It was the first time the agency had conducted tests that involved joint participation by two of its science programs, biology and physical sciences, says Zea, who started the project with NASA. “I think it stresses the importance of interdisciplinarity because we need to be able to bring together these different disciplines to find solutions to real-world problems.”
Biofilms are also an important medical problem on Earth, particularly on medical devices or implants including catheters, where they can lead to significant disease problems. Varanasi says the same type of fluid-saturated surface may also have a role to play in helping to address these issues.
The project was supported by NASA and used facilities provided by many other companies and organizations.
(tags for translation)Kripa Varanasi