Polyethylenimine coated TiO₂ nanoparticles as antimicrobial agents

In recent years, antibiotic-resistant bacterial infections have become a growing concern. Various polymer-based antimicrobial strategies have emerged in order to provide a solution to this global clinical problem. Inspired by antimicrobial peptides (AMPs), a plethora of antimicrobial cationic polymers have been developed. These polymers mainly consist of two functional components, cationic groups and hydrophobic groups, both of which were shown to be essential for the polymers potent and selective activity against several strains of bacteria. Polyethylenimines (PEI) are a group of synthetic cationic polymers with a wide range of molecular weights. The polymers are produced as a linear or branched PEI (l-PEIs/b-PEIs), and like other cationic polymers exhibit significant and extensive antimicrobial activity against Gram positive and negative bacteria, yeast and fungi. In this study, titanium dioxide nanoparticles (TiO₂-NPs) which are known for their excellent biocompatibility, high chemical stability and low toxicity, were coated with l-PEI or b-PEI in different MW in order to create nanoparticles with antimicrobial activity. The hypothesis underlining this research is that the TiO₂-NPs coated with PEI provide the necessary cationic charge density and amphiphilic structures needed to induce membrane disruption or permeabilization, leading to antibacterial activity at lower concentrations than free polymer. Characterization results indicate a presence of PEI on titanium nanoparticles surface. TEM images of the nanoparticles confirms that they are 70-300nm in diameter, in agreement with DLS measurements showing that the particles are between 100 and 350 nm due to the hydrated polymer coating. Particles show more positive ζ-potential in accordance with more PEI incorporated as expected. The antimicrobial activity of TiO₂-PEI and PEI against E.coli were examined by following their effects on growth curves of the bacteria. Preliminary results showed TiO₂-PEI NPs with comparable concentration of PEI achieved higher growth inhibition of E.coli then free polymer solution.