Persistently Antimicrobial Polyurethanes for Improved Pressure Garment Bladders

NASA is seeking improvements to current spacesuit pressure garment bladders in several key areas, including increased microbial resistance, imparting self-healing capabilities, and decreasing the friction between the bladder and surrounding materials. To create these improvements, TRI Austin proposes further development of new polyurethane materials that were demonstrated in Phase I to have antimicrobial properties, with greater than 99.9% reduction in both gram-positive and gram-negative bacteria, while maintaining excellent thermomechanical properties. This polyurethane will be used as a drop-in replacement for the current polyurethane coating material used in legacy space suit pressure garment bladders. This new polyurethane was created incorporating novel antimicrobial additives which make polyurethanes, as well as other polymers, persistently antimicrobial. These new polyurethanes are expected to decrease or even eliminate the need for biocide use in next-gen space suit applications, without causing significant changes to the current production or processing methods. In addition, minimizing friction with surrounding materials will be investigated as these polyurethanes are refined. TRI Austin will work with the current producer of pressure garment bladders to ensure the new polyurethane is a drop-in replacement for the legacy material. The new formulation will be iteratively refined and scaled until a polyurethane is created which satisfies or exceeds all of NASAs desired requirements. These materials will then be used to create a spacesuit arm assembly and tested at the component level. Current polyurethanes used in EVA spacesuit pressure bladders suffer from a few key drawbacks including a lack of antimicrobial character, the inability to self-heal small punctures, and significant friction with surrounding materials. TRI Austin proposes improving the antimicrobial properties of current EVA spacesuits through further development of new polyurethane materials that were demonstrated in Phase I to exhibit greater than 99.9% reduction in both gram-positive and gram-negative bacteria, while maintaining excellent thermomechanical properties. These polyurethanes impart persistent antimicrobial character via additives that are bound to the polymer and, in contrast to typical silver-based antimicrobial additives, will not leach out or decrease in effectiveness over time. These materials are expected to mitigate the need for biocide use in next-gen spacesuits. Additionally, since the legacy material is also a polyurethane, no significant changes to the current production methods are predicted. Formulations and methods relevant to friction reduction will also be investigated. During Phase II, TRI Austin will further optimize the antimicrobial polyurethane developed in Phase I. The formulation will be iterated to enhance the thermomechanical properties, decrease the gas permeability, decrease the friction and wear properties, and improve other key criteria, as defined by NASA, while maintaining the antimicrobial characteristics. This optimized material will be scaled to volumes appropriate for the formation of yards of laminated composite fabric, and the composite fabric produced. This fabric will be tested for compliance to NASA requirements. The fabric will also be tested for its antimicrobial properties with a full battery of microbial testing. Simultaneously to the scale up and production of the fabric, testing will be performed in an ongoing manner to confirm that no processing methods adversely affect any of the properties of the material, including the antimicrobial properties. Other necessary testing, such as flammability, density, and tribology will be performed, as agreed. Deliverables to NASA will include scheduled technical progress reports and a final report that will document the research and development activities and results obtained during Phase II. Material samples of the final polyurethane and any resulting composites shall also be provided to NASA. Finally, an arm assembly will be produced and provided to NASA for further testing.
Benefits: Potential NASA applications include new materials for pressure garment bladders for integration into the Exploration Extravehicular Mobility Unit (xEMU) and used in a variety of space-based missions including on the International Space Station (ISS), and in future missions to both the Moon and Mars. Additionally, this material could be used in other applications that require both flexibility and antimicrobial properties, such as water reservoirs, water cooling tubing, and drink pouches. Applications could include use as persistent antimicrobial coatings and films such as those used for food manufacturing, medical devices, marine diving, water containment, sewage treatment, CBRN protective suits, and creation of antimicrobial surfaces, at the industrial and consumer level. The new material may also be used by the U.S. DoD in flight suits and coatings for water containment systems.