SBIR-STTR Award

Silver is used as a biocide for disinfection in the water treatment and supply system of spacecraft. However, its short lifetime result in high operating costs and risk of biofilm development. The innovation of this NASA STTR project relies on the development of novel surface coating chemistries able to extend the lifetime of nanosilver-based antimicrobial coatings, used in water treatment systems of spacecraft, without affecting their anti-biofouling performance. The overarching hypothesis is that silver nanoparticles can be passivated by partial sulfidation, forming Ag/Ag2S core-shell structures with low silver leaching rate but excellent long-term biocidal properties. This project will the optimal physicochemical properties that balance dissolution rate and biocidal activity in nanosilver. Then, we will develop the in situ nucleation and passivation conditions able to generate the desired particle properties on stainless steel and surfaces relevant for spacer water treatment systems. Dissolution rate, biocidal properties, and biofilm development kinetic will be followed over time to demonstrate the long-term performance of the partially sulfidized nanosilver coatings. The results of this project will lead to the development of a passivated surface coating generator technology to be used in spacecraft systems for sustained biofouling control. Potential NASA Applications (Limit 1500 characters, approximately 150 words) U.S. space exploration missions have long considered returning to the Moon and exploration of Mars that challenge life support systems. A potable water treatment process is needed to prevent microbial growth in the water storage and distribution system for long duration missions. Silver ions have been proven by NASA to be effective for microbial control, however, there remain significant challenges on its fast dissolution rate for an effective solution at preventing biofilm formation. Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words) Water treatment and medical is the biggest end-use applications of antimicrobial coatings. Medical professionals and manufacturers are increasingly incorporating silver into a wide array of applications, including wound and burn care, consumer appliances, textiles and clothing, wood preservation, water purification, commercial food and beverage preparation, furniture, building materials and more.

Silver nanoparticles (Ag NPs) are used for the functionalization of surfaces in order to achieve antimicrobial properties and control biofilm growth. The antimicrobial activity of Ag NPs is attributed to the release of Ag + ion, which means that Ag NPs need to be soluble to achieve microbial inactivation. However, because of this constant silver release, Ag NPs rapidly dissolve away from the surface, depleting the biocidal activity and limiting the use of Ag NPs for long term biofouling control. In Phase I of this project, the team led by Cactus Materials Inc. demonstrated that Ag NPs can be passivated with less soluble forms of silver, such as Ag 2 S, AgBr, or AgI, to slow down silver release and extend the lifetime of Ag NPs-based antimicrobial coatings. When different passivation chemistries were compared, sulfidation of Ag NPs was found to have the best performance in terms of both slow silver release and high antimicrobial performance. The improved anti-biofouling performance is attributed to the higher retention of silver on the surface over time. A green chemistry approach was developed to functionalize surfaces in situ using a flow through system with reagents of Toxicity Class II or lower. The passivated silver coatings were shown to be compatible with the current use of aqueous AgF for water treatment and storage in the International Space Station. Phase II of this project will evaluate how to coat surfaces comprised of different materials or having complex morphologies with the passivated silver coating developed in Phase I. Long term anti-biofouling performance will be assessed in a dormancy scenario of up to a year. Release of chemicals and particles during the dormancy period will be assessed to identify any risk to the water quality from long term exposure to the passivated silver coatings. The results of this research will establish the capacity of the proposed innovation to control biofilm in a wide variety of structures for extended periods of time. Potential NASA Applications (Limit 1500 characters, approximately 150 words) U.S. space exploration missions have long considered returning to the Moon and exploration of Mars that challenge life support systems. A potable water treatment process is needed to prevent microbial growth in the long duration missions. Silver have been proven by NASA to be effective for microbial control, however, there remain significant challenges on its fast dissolution rate for an effective solution at preventing biofilm formation. In addition to, another application is in water processor assembly (WPA) here biofoulings are persistent Potential Non-NASA Applications (Limit 1500 characters, approximately 150 words) There are unmet needs in current pandemic environment to disinfect tough surfaces including vehicles, air transportation, mass transits and many others. This coating system is expected to antimicrobial at the surface and maintain antimicrobial activity despite wear and environmental exposure. Other applications are included water membranes, textile cloths, and medicals metallic coatings