Controlling Silver Release from Antimicrobial Surface Coatings for Biofouling Control

Silver nanoparticles (Ag NPs) are used for the functionalization of surfaces in order to achieveantimicrobial properties and control biofilm growth. The antimicrobial activity of Ag NPs is attributed to therelease 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 bepassivated with less soluble forms of silver, such as Ag 2 S, AgBr, or AgI, to slow down silver release andextend 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 silverrelease and high antimicrobial performance. The improved anti-biofouling performance is attributed to thehigher retention of silver on the surface over time. A green chemistry approach was developed tofunctionalize surfaces in situ using a flow through system with reagents of Toxicity Class II or lower. Thepassivated silver coatings were shown to be compatible with the current use of aqueous AgF for watertreatment and storage in the International Space Station.Phase II of this project will evaluate how to coat surfaces comprised of different materials or havingcomplex morphologies with the passivated silver coating developed in Phase I. Long term anti-biofoulingperformance will be assessed in a dormancy scenario of up to a year. Release of chemicals and particlesduring the dormancy period will be assessed to identify any risk to the water quality from long termexposure 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. This project proposes to improve the long-term performance of silver-based surface coatings used for biofouling control on various surfaces. The core-shell (CS) structure extends the lifetime of antimicrobial coatings and increases its overall performance for biofouling control over time. The coatings can be applied in situ in systems prone to biofouling, such as Water Processor waste tanks, without the need of disassembly. It is therefore an ideal approach for space conditions, where simple chemistry and processes are preferred. The novelty of the approach lies in the careful control of the silver passivation stage, which result in an CS structure that retain good antimicrobial performance despite their reduced solubility. To develop this discovery into a viable process for antimicrobial surface coatings, the limits of sulfidation where antimicrobial performance is preserved needs to be identified, and the scaled-up reaction conditions that can lead to such coatings in a system without requiring its shutdown or disassembly need to be established. Objective 1: Form homogeneous nanosilver coatings on surfaces of complex geometries using an in-situ surface functionalization approach Milestone for objective 1: Identify the optimal conditions for the formation of a homogeneous coating of passivated nanosilver in a stainless steel below. Objective 2: Identify the coating efficiency on different types of surfaces present in the WPA. Milestone for objective 2: Identify the type of surfaces that will be the most amenable to passivated nanosilver coatings. Objective 3: Evaluate the long-term biofouling resistance of a bellow tank system in function of the silver content of the surface. Milestone for objective 3: Demonstrate the formation of a stable coating having the properties identified in objectives 1 and 2 on stainless steel. Objective 4: Characterize the change in water quality over time in water tanks coated with passivated silver. Milestone for objective 4: Identify the conditions that will ensure minimal risk by passivated nanosilver coatings by ensuring that water quality standards are met. Objective 5: Phase III product and business planning Milestone for objective 5: Develop products and production scheme Objective 6: Reporting
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