Stimuli-responsive antibacterial coatings
Abstract
The goal of this thesis is to develop potential solutions to prevent bacterial growth on surfaces, using stimuli-sensitive antibacterial coatings. First, pH-sensitive coatings were synthesized using phosphonium monomers with different substituents, along with two different types of crosslinkers: one ketal-based and the other acetal-based. These components were combined and subjected to UV curing. Analysis of coating properties revealed a mild hydrophilic character, along with high charge density and gel content. Degradation studies of these coatings, employing ketal or acetal-based crosslinkers, demonstrated that ketal-based coatings underwent faster degradation at pH 5.0 compared to acetal-based coatings, resulting in the release of more phosphonium species at pH 5.0. Furthermore, antibacterial studies showcased the bactericidal efficacy of these pH-sensitive phosphonium coatings. At pH 5.0, ketal-based coatings exhibited superior performance, leading to complete eradication of Staphylococcus aureus and Escherichia coli, as confirmed by the counting of colony forming units and fluorescence microscopy analysis using green fluorescence protein-expressing bacteria. Further enhancements to these pH-sensitive phosphonium coatings were made by incorporating the antibiotic gentamicin. A gentamicin monomer with the drug conjugated to a polymerizable styrenic group through a pH-sensitive imine linkage was incorporated into the coating formulation. Analysis of coating properties revealed a higher hydrophilic feature and a slight enhancement in gel content compared to the non-gentamicin coatings. Drug release studies demonstrated that gentamicin was released more rapidly when utilizing ketal-based coatings compared to acetal-based coatings. Bacterial studies indicated complete eradication of bacteria irrespective of the coating composition. Additionally, thermo-sensitive coatings were explored in combination with inductive heating. Combinations of different antibiotics and poly(ester amide) were utilized, and the final coatings were obtained through drop casting. Upon reaching a temperature above the glass transition temperature of the poly(ester amide), antibiotics were released at an accelerated rate. Various temperature conditions were explored to assess the thermo-responsive behavior of the poly(ester amide), including the application of inductive heating. Higher temperatures led to more rapid release of the drug. Bacterial studies revealed that these coatings, when subjected to inductive heating combined with antibiotic release, exhibited an enhanced bactericidal effect confirmed by crystal violet and fluorescence microscopy.