Testing the bactericidal ability of a polycationic molecule to design self-healing surfaces

The need for antimicrobial surfaces is obvious because of ever growing demand for healthy living, thus a material that can kill harmful microorganisms is of great interest. The idea discussed in this thesis is to combine the techniques of Photo Dynamic Therapy (PDT) and self sterile surfaces to design self-healing surfaces.

We modified one pyridine ring of Tetro-meso (N-methyl pyridyl) porphyrin (T₄MPyP) to obtain 5-(4-carboxyphenyl)-10, 15, and 20-tris-(N-methyl-4-pyridlium) porphyrin. This modified porphyrin was reacted with Vinyl benzyl chloride polymer via a nucleophilic substitution reaction forming an ester linkage between polymer and porphyrin. The above molecule was then tested for its bactericidal property.

The thesis explains in detail the protocols and procedures used for bacterial analysis. It also explains the synthesis of poly (styrene-co-4-vinyl benzyl chloride) [poly (St-co- VBC)] and 5-(4-carboxyphenyl)-10, 15, and 20-tris-(4-pyridyl) porphyrin. This porphyrin was then converted to a salt by reaction with iodomethane and attached as a pendant group to a co-polymer chain. This was completed to determine whether porphyrin retained its bacterial killing ability when attached to the co-polymer backbone. The attachment of the porphyrin to the polymer while retaining its antimicrobial activity is important to design self healing surfaces.

Coatings of this polymer solutions were obtained by painting the bacteria sprayed slide with 40μl of the polymer solution. The antimicrobial ability of these polymer coated slides was observed by subjecting them to photo inhibition. Staphylococcus aureus (ATCC, strain 33807) and Escherichia coli (ATCC, strain 492316) were used to complete all our experiments.

The polycationic porphyrin salts killed the bacteria when exposed to light. The photosensitized porphyrins (T₄MPyP and modified porphyrin) worked for two kinds of illuminated lights (Incandescent light bulb and fluorescent light bulb). The aim of this project to design self-healing antimicrobial surfaces where the antimicrobial molecule is a pendant group on a polymer backbone was successful. The cationic porphyrin when attached to the VBC co-polymer as a pendant group retained its antimicrobial ability. This is very encouraging and motivating to pursue our proposed goal of designing selfhealing surfaces further.