UC Davis

The frequent outbreaks of foodborne and waterborne diseases have become a serious public health issue, which is related to the presence of microbial biofilms on surfaces of materials. Current research activities aiming at reducing or eliminating the biofilm formation could be mainly divided into two major approaches: an active approach of “attacking”, by killing the microbes once they are attached to the material surface; and a passive approach of “defending”, creating resistance to microbial attachment or releasing the attached one. In this dissertation, a dual-functional structure was initially proposed: rechargeable biocidal moieties immobilized at the inner layer, and antifouling moieties serving as a protective layer located on the outside of the surface. With a such unique surface structure, once microorganisms approach the designed surfaces, (i) the antifouling moieties could reduce the non-specific adsorption of the microorganisms and make them difficult to adhere; (ii) any live bacteria attached on the surface could be immediately killed by the incorporated biocidal moieties; (iii) any resulting cell debris and other biofoulants could be easily washed off with mild hydrodynamic force applied; furthermore, (iv) the consumed biocidal activity could be regenerated by either chlorination or photoirradiation. Overall, I designed and successfully developed three types of rechargeable biocidal and antifouling functional materials, which exhibited great potentials in food packaging, water filtration, and medical application areas.Specifically, in this dissertation, chapter 1 briefly introduces processes and mechanisms of microbial biofilm formation, two major strategies responding to avoid and reduce the formation of biofilm, and typical chemicals with rechargeable biocidal or antifouling functions applied in recent years. In chapter 2, a new antibiofilm concept combining both rechargeable antimicrobial and antifouling functions was proposed. An N-halamine precursor, N,N-diallylmelamine (DAM), and a zwitterionic monomer, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), were covalently bonded onto poly(vinyl alcohol-co-ethylene) (PVA-co-PE) and generated a double-layer structure. The outside surface embedding with resisting and releasing functions and the inner layer with regenerable biocidal activities work constructively to limit the biofilm development. In chapter 3, a new synthesized zwitterionic polymer, sulfonated polyethyleneimine (PEI-S), was chemically bonded with an N-halamine grafted PVA-co-PE nanofibrous membrane. The obtained PEI-S@BNF nanofibrous membrane with the super-high specific surface area did effectively magnify the interfacial effect. Two engineering models were constructed to explain the resisting and releasing mechanisms via typical isothermal adsorption and release experiments. Additionally, the final product, PEI-S@BNF nanofibrous membrane, showed great potential to be applied as a water filtration material. In chapter 4, instead of N-halamine, a photo-induced biocide, benzophenonetetracarboxylic dianhydride (BPTCD) was incorporated onto the PVA-co-PE nanofibrous membranes, providing a photo-driven regenerable biocidal function. After combined with antifouling moieties, the obtained SBMA@EVOH also exhibited a desirable antibiofilm effect, which proved the universality of such proposed bifunctional antibiofilm strategy. In chapter 5, a N-halamine-based chlorine rechargeable antimicrobial composite fabric (HCF) was fabricated via an industrial scalable dip-coating method. An imide/amide halamine grafted cotton fabric (DMH-g-cotton) served as a reinforcement component and a reservoir of active chlorine. And an amine halamine polymer (PVA-co-PE-g-DAM) as a coating component could reduce the loss of active chlorine, realizing long-term killing performance. With such a unique combination, the designed HCF could be considered as a potential active food-contact material that could effectively reduce microbial cross-contamination, prolong the food lifetime, decrease food spoilage, and ensure food safety. The final chapter describes all achievements related to the proposed multifunctional double-layer surface structure, which could significantly reduce the biofouling effect via resisting, killing, and releasing pathways, and a practical demonstration of biocidal functional composite fabric applied as a food-contact material.