Understanding Biofilms : Plasma Polymer Coatings to Prevent Biofilm Formation and Understanding the Chemical Pathway to Their Formation by Spectroscopy

Crisp, Amy and Rehman, Ihtesham and Cheneler, David and Short, Robert and Ashton, Lorna (2024) Understanding Biofilms : Plasma Polymer Coatings to Prevent Biofilm Formation and Understanding the Chemical Pathway to Their Formation by Spectroscopy. PhD thesis, Lancaster University.

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Abstract

Biofilm is the name of microbial communities, where microorganisms irreversibly adhere to each other and a surface, whilst encompassed by a complex extracellular matrix. Biofilms are ubiquitous throughout the world, but in the healthcare system they pose a significant threat, particularly in the infection risk of blood contacting materials. Once an infection progresses to a biofilm, there are limited effective treatment options to completely eradicate them. A substantial issue in clinical management is identifying when the microbes in an infection have switched from a planktonic to a biofilm phenotype. Despite efforts to develop new treatments, due to the adaptable nature of microorganisms and the mounting antimicrobial resistance crisis, prevention is the best option to combat biofilm infection mortality. A proposed solution is to treat all blood contacting materials with an anti-biofouling coating. In this research project, both biofilm diagnostics and coatings to prevent biofilm growth have been investigated. Vibrational spectroscopy can reveal the precise chemical composition of natural materials, whilst remaining non-destructive and requiring minimal sample preparation. FTIR has been successfully applied in this work to identify chemical markers of intact bacterial (S. epidermidis) and fungal (C. albicans) biofilms, and for the first time FTIR has chemically defined the timeframe for irreversible attachment to a substrate. This foundational study provides a baseline to support FTIR for implementation in clinical diagnosis to identify infection maturity, informing treatment options. Plasma polymerisation has been utilised to produce and initiate anti-biofouling coatings on a diverse range of clinically relevant materials. In this research, the aim was to maximise ethylene oxide content on a given surface, naturally increasing the hydrophilicity to reduce protein adsorption. Firstly, the γ-regime (high pressure and low power) was applied to crown ether monomer, to optimise the functional group retention and results show the new polymer coating approached the ethylene oxide retention observed in an industry standard coating. In an adjoining study, the ultra-thin industrial hyperbranched polyglycerol coating has been rigorously monitored across 7 different materials, including clinically relevant nitinol stents. Vitally, results are presented for the novel application of ion-milling X-ray photoelectron spectroscopy, after a protein adsorption test, indicating HPG can prevent protein penetration within the coating structure. Further evidence for HPG having high non-biofouling capability was revealed in biofilm exposure testing that used vibrational spectroscopy to define the timepoint of biofilm initiation. While further work is required to produce an optimal crown ether plasma polymer coating, HPG should soon be suitable for clinical trial.