Bio-based nonionic antimicrobial polymers with isatin or indole functionality

Infections by pathogenic microorganisms remain one of the most serious concerns in several areas, particularly in hygienic applications. Antimicrobials have been used to combat these infections. Using small molecular antimicrobials as additives or coatings is an industrially adopted strategy. However, small antimicrobial agents always suffer from many drawbacks, such as leaching potential, toxicity to the environment, antimicrobial resistance. The development of antimicrobial polymers provides a promising strategy to overcome these issues. Compared to small molecular antimicrobials, antimicrobial polymers have advantages like enhanced antimicrobial efficiency, reduced toxicity, longer lifetime and lower risk to develop antimicrobial resistance.

Most research has been focused on cationic antimicrobial polymers which can disrupt bacterial membranes by electrostatic interactions. The major issues with cationic antimicrobial polymers are their undesirable high-water solubility, toxicity, fouiling potential and poor miscibility with nonionic polymer matrices. To solve these problems, continued exploration of new nonionic antimicrobial polymers is highly valuable and that is where this thesis has been focusing on.

In this work, we have designed and synthesized different nonionic antimicrobial polymers with isatin or indole functionality, including hyperbranched and linear structures. The antimicrobial properties against various bacteria of these polymers were evaluated. In general, these bio-based polymers exhibited significant antimicrobial activity, higher than their corresponding small model compounds. We also found that ether unit may have a synergistic effect to interact with certain bacterial membranes. It was also observed that the N-H moiety of indole in the polymer’s structure facilitate the hydrogen bonding with the C=O moiety of polyesters, which improved their miscibility. Finally, we evaluated the hemolytic activity and cytotoxicity of the obtained polymers. As a result, they showed negligible cytotoxic effect to red blood cells and MG-63 osteoblast-like cells, which indicates their potential in biomedical applications.