Description: This project proposes to improve the long-term performance of silver-based surface coatings used for biofouling control on various surfaces. The innovation includes the generation of nanoscale silver particles (Ag NPs) on the surface, which provides high surface area for biocidal action, and their subsequent passivation by the formation of a silver sulfide (Ag2S) shell for a slower silver release. The Phase I proposal for this work was submitted to respond to specific needs of NASA described in the subtopic T6.06 as “NASA is seeking methods to maintain concentrations of biocidal silver (0.05 – 0.4 mg/L) in potable water including surface treatments that may limit silver loss.” In Phase I of this project we focused on demonstrating the antimicrobial and anti-biofouling performance applied to stainless steel surfaces, and can be applied applied in-situ using a flow-by technique with low toxicity reagents (Class II or lower). In Phase II of this project, we demonstrated coating of structures with complex geometries with Ag/Ag2S NPs at various compositions using the flow-by method developed in Phase I. An automated system was built to apply the coating. To expand the application of Ag/Ag2S NPs on other space applications, coating of the NPs was done on Inconel and Titanium. To develop this technology into a commercial product for space and non-space related applications, in Phase II-E of this project, we will evaluate the stability of the Ag/Ag2S NPs coating on the metal surfaces against mechanical stresses especially during the shuttle launch by random vibration test. The optimization of coating metal surfaces (stainless steel and Inconel) with Ag and Ag/Ag2S NPs using thermal and cold spray will be done. Finally, biofilm formation resistance of the coated stainless steel with Ag and Ag/Ag2S NPs will be investigated in an environment simulated based on the condensing heat exchangers in water process assembly (WPA) in ISS.

Benefits: WPA units: The CoreSil coating on various structures such as bellows, pipes, tanks, and others can eliminate biofouling and meet NASA astronaut safety requirements. In-situ sulfidized AgNPs (CoreSil) coating for microbial control in future space exploration, Gateway mission, lunar, and Mars: The CoreSil coating can overcome the challenge with the slow-release property to address Ag NPs fast dissolution at preventing biofilm formation. Heat exchanger unit: The CoreSil coating can prevent biofilm formation in potentially heat exchanger system.

Water treatment systems with metal parts: Coating tanks, pipes, elbows, and corrugated plates in water treatment systems. Reverse osmosis (RO) membranes: Biofouling on RO membrane can be preventable using CoreSil Technology coating Antimicrobial textile: Microbial growth on clothes reduces the lifetime of the clothes; preventable using CoreSil