Controlling Silver Release from Antimicrobial Surface Coatings for Biofouling Control

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 appliedin-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: 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 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