(436b) Evaluation of Bacteria Resistant Thin Films for Long Duration Space Applications

Bacteria has been isolated from multiple surfaces in the International Space Station (ISS) because of the naturally occurring human microbiome. Therefore, methods to mitigate bacteria transmission and colonization will enhance the success of long duration space travel. The NASA Student Payload Opportunity with Citizen Science (SPOCS) program provided the opportunity for teams of students to design, build, and fly a payload to the International Space Station (ISS). Further, the SPOCS program required the integration of citizen science into the project, to inspire the next generation of NASA researchers and scientists. A team from the University of Idaho participated in the SPOCS program by designing and building an experimental system to evaluate the performance of a bacteria resistant thin film hydrogel whose composition was selected by citizen scientists. The thin film was applied to aluminum substrates as an analogue to the handles located throughout the ISS, and Staphylococcus epidermidis was selected as representative bacteria strain that can be passed from person to person via high contact surfaces.

In the first stage of this research, a test kit was designed and distributed to 200 local third through fifth grade students. The kit contained two randomly selected polymer hydrogel chemistries, an unlabeled positive control hydrogel, growth media, and sampling and evaluation supplies. Each participating citizen scientist was tasked with swabbing a high contact surface in their home, followed by transferring the swab and its bacteria to each of the hydrogels in their kit. Bacteria growth was encouraged with nutrient-rich media and additional swabs were added weekly over the course of four weeks. Throughout the experiment, the citizen scientists monitored the overall surface coverage of bacteria for each of their samples, and after four weeks the students ranked their samples from most bacteria to least bacteria. These results were used to down select which polymer coatings would be evaluated in the ISS microgravity experiment, with the two best performing hydrogels being an equimolar distribution of [2-(aryloyloxy)ethyl] trimethylammonium chloride (TMA) and 2-carboxyethyl acrylate (CAA) monomers, and an equimolar distribution of TMA and 3-sulfopropyl methacrylate (SA) monomers.

In parallel, a 1.5U Nanoracks NanoLab experimental platform was designed for testing the impact of microgravity on bacteria adhesion to these polymeric coatings. This included consideration of safety and operational constraints on the ISS, evaluation of potential pressure build-up, design of the bacteria introduction device, layout of the substrates within the experimental space, and operation of the electrical components. The most notable design constraints were the inclusion of Biosafety Level 1 bacteria, the inclusion of liquid nutrient broth which required secondary containment, and the operational constraints applied for this payload.

The payload was launched to the ISS in December 2021 and the payload was returned to Earth in January 2022. Following return, the samples were evaluated for their overall surface coverage of bacteria, using both photography and confocal microscopy. Further, the influence of location within the payload was evaluated for the two thin film hydrogel coatings and the uncoated control substrates. Lastly, the results obtained from the microgravity experiment were compared to an analogue system that was run under the influence of gravity on Earth, in order to identify the role that microgravity plays on the performance of these bacteria resistant thin film coatings.