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Our objectives are to eliminate bacteria common in processing/packaging facilities by applying a super-repellent antimicrobial coating on various surfaces (including equipment, interior wall, ceiling, drain, storage tank, etc.) in the facility. The nanostructured coating can effectively repel most of the bacteria, and kill the rest that manage to adhere to the surfaces in the facility to ensure food safety.<P> Our goals are two-fold: (1) to synthesize and characterize super-repellent antimicrobial polymeric coatings; (2) to examine the antimicrobial properties and establish structure/property relationships for these coatings. In our targeted super-repellent antimicrobial coatings, the antimicrobial moieties (quaternary ammonium groups) will be covalently bonded to the polymer matrix, preventing them from leaching out into food. <P>The outputs of this project include: (A) Activities: (1) Preparation and characterization of smooth antimicrobial coatings; (2) Preparation and characterization of nanostructured, super-repellent antimicrobial coatings; (3) Preparation and characterization of mechanically robust, super-repellent antimicrobial coatings; (4) Antimicrobial tests, with the aim at understanding the mechanism of antimicrobial actions (killing and/or repelling of bacteria); (5) Mentoring a graduate student. (B) Events: Reporting project findings, when appropriate, in relevant conferences and symposia. (C) Products: Potential patent applications; Peer-reviewed journal publications.
Non-Technical Summary: Unsafe food and food poisoning due to insufficient protection from pathogenic bacteria results in human suffering from illness and tremendous financial repercussions. Numerous outbreaks in the U.S. were due to contaminated food processing facility. Therefore, it is of extreme importance to prevent the accumulation of pathogenic bacteria inside food processing facilities. Our objective is to develop super-repellent antimicrobial nanostructured coatings for food processing facilities (both food contact and non-contact surfaces) to eliminate a major external source of bacterial infection for food. The super-repellent antimicrobial coatings, which are topographically structured to mimic the lotus leaf surface (i.e., dual-scale structure), will combine two mechanisms of eliminating bacteria into one system: repelling (due to super-repellency against both water and oil) and killing (due to covalently bonded quaternary ammonium groups at the coating surface). The innovative antimicrobial coatings can be applied to food processing facilities and peripheral surfaces (drains, floors, storage tanks, apparel, etc.), and have the potential to greatly reduce bacterial attachment and biofilm formation, thus reducing foodborne pathogens. Moreover, the technology to be developed may also find applications in healthcare settings, personal hygiene industry, biomedical industry, and other high-touch, high risk environments, making significant contributions to a better and safer society. <P> Approach: Our planned research will be divided into the following main tasks: (1) Smooth antimicrobial coatings. We will prepare smooth antimicrobial polymer coatings by using a surface segregation strategy to examine whether covalently bonded antimicrobial species still have antimicrobial properties. Via this approach, the antimicrobial moieties such as quaternary ammonium compounds (QAC), will be segregated at the coating surface (it is unnecessary to have antimicrobial groups in the bulk of a coating) and, in the meantime, chemically bonded to the cross-linked polymer network. The key in our approach is that the QAC groups will be connected to a fluorinated or silicone (PDMS) chain (low surface-energy species), which provides the driving force for the QAC-containing moiety to segregate at the coating surface. (2) Super-repellent antimicrobial nanostructured coatings. To eliminate bacteria in a more effective way, i.e. combining repelling bacteria with killing bacteria, we aim at preparing super-repellent antimicrobial nanostructured coatings with a raspberry-like surface topography. The raspberry-like nanosized structure is expected to reduce significantly the anchoring area for microbes, making it very difficult for them to attach. In addition, the presence of perfluorinated QAC groups will make sure that those tenacious bacteria, which manage to adhere to the surface, are killed upon contact with the super-repellent surface. Therefore, the super-repellent antimicrobial coatings will allow both contact-killing and maximum repelling of bacteria. (3) Antimicrobial tests. Initial events in microbial adhesion will likely play a role in the final biofilm structure. Our goal is to stop the biofilm process before it can take anchor with our super-repellent coatings. For tenacious bacteria, which overcome the super-repellent barrier, we further aim to demonstrate bactericidal properties against two common foodborne sources of infection, E. coli and Salmonella. Exposure of coated surfaces to these bacterial solutions will allow us to determine the minimum inhibitory content (MIC) of the antimicrobial on the surface. The following samples will be primarily used for antimicrobial tests: smooth antimicrobial coatings (biocidal assessment); super-repellent coatings with no QAC, compared to smooth fluorinated coatings (biostatic assessment: inhibit ability to attach); and super-repellent antimicrobial coatings (biocidal assessment: kill tenacious bacteria). To verify whether the antimicrobial action is due to the combination of a bactericidal effect and a repellent effect, live/dead cell analysis using flow cytometry will be performed after bringing the test strains in contact with the active coating. We will run antimicrobial leaching tests to confirm that the covalently attached antimicrobial groups remain bound to the nanostructured coatings. We will also examine the durability of these coatings.