Self-Stratifying Antimicrobial Coatings

Abstract

Today, antimicrobial polymers/coatings are widely used in various areas, such as biomedical devices, pharmaceuticals, hospital buildings, textiles, food processing, and contact lenses, where sanitation is needed. Such wide application facilities have made antimicrobial materials very attractive for both academic and industrial researchers. Many methods have been developed to produce such materials with different properties. The aim of this PhD study was developing a novel method to prepare environmentally benign, surface active, long lasting antimicrobial surface coatings. This method was also targeted to be a simple one, so that it can be manufactured on an industrial scale and can be applied in our daily life. In Chapter 2 and 3, we developed low surface energy polyurethane films by tethering antimicrobial quaternary ammonium compounds to the polymer network covalently. These compounds were designed and synthesized to diffuse towards the film/air interface during the film curing. In this way, a higher antimicrobial moiety concentration on the film surface was targeted. This property was gained to the QACs by attaching either long hydrocarbon (QACs 1 and 2) or perfuorinated (QACs 3 and 4) hydrophobic tails. QAC enrichment at the film surface was confirmed by dynamic contact angle measurements and X-ray photoelectron spectroscopy techniques. Overall, all of the QAC-containing films showed strong antimicrobial activities against the tested bacterial species. Of all systems tested, number 3 was the most effective with a 5 log10 reduction of both bacterial species observed at all concentrations applied. With the long perfluoroalkyl tail, QAC 3 was found to be the most efficiently diffusing QAC towards the film surface. As a result, the number of QAC molecules per cm2 was much higher for system 3 than for the other systems. This suggests that the most hydrophobic nature of QAC 3 resulted in the highest antimicrobial effect. The shorter spaced QAC-containing system 2 was the least effective of all four systems. We obtained minimally desired 3 log10 reduction only with higher QAC concentrations for this system. Also, we found that system 1 was slightly more active against the much simpler Gram-positive S. aureus bacteria than the complex Gram-negative E. coli. In Chapter 4, we investigated a possible antimicrobial activity of some commercially available ionic liquids. These liquids were never used for this purpose before. The covalent incorporation of these liquids to our polyurethane network ended up with very successful antibacterial results. Hence, we successfully reported an ionic liquid based antimicrobial surface coating for the first time in the literature. Moreover, in environmental point of view, leaching of the active QAC compounds from the films to the exterior was investigated by monitoring bacterial inhibition zone around the film samples and the antimicrobial tests of the extraction solutions of the films. None of the prepared films showed any trace of leaching out confirming all the quaternary ammonium compounds were covalently bonded to the polyurethane backbone. Finally, we tried another method to prepare targeted antimicrobial coatings in Chapter 5. Instead of using self-diffusion ability of hydrophobic quaternary ammonium compounds, we utilized hydrophilic QAC structures to enrich at the film surface by forcing them to diffuse with an external attractive layer. However, we found this method impractical after facing numerous problems.