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Title: Fabrication and characterisation of antimicrobial surfaces
Author: Sorzabal Bellido, I.
ISNI:       0000 0004 7428 7227
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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Bacterial infections cause more than 6 million deaths worldwide. For about a century, antibiotics have been the primary resource to fight bacterial infections, however, emergence of antimicrobial resistance is undermining their effectiveness. Controlling initial stages of bacterial infection and spreading of antimicrobial resistance is not only essential to save millions of lives, but also to reduce the waste of economic resources in strategical sectors. In this respect, surfaces play a critical role, contributing to infection spreading and formation of biofilms. In this thesis we present different strategies that can be used to characterise and fabricate surfaces resistant to bacterial colonisation, which could be potentially used to inhibit biofilm formation and development of antimicrobial resistance. Chapter 2 gives a general overview of the main characterisation techniques used throughout the thesis, allowing to unravel the surface chemistry and the antimicrobial performance of different surfaces. The techniques presented include photoemission (i.e. XPS) and vibrational spectroscopies (i.e. ATR-FTIR and Raman), which were used to investigate the chemical properties of antimicrobial interfaces. The biological processes at the surfaces were characterised by combining SEM and fluorescence microscopy, using specific methods developed during the course of the thesis. Chapter 3 describes a multi-step post-functionalisation method to import antimicrobial functionalities to a silicone-based material used in medical devices. This method included the incorporation of a covalently-attached biocompatible compound used to load a model antimicrobial agent (i.e. salicylic acid) onto the interface. Functionalised interfaces showed remarkable antimicrobial performance against E. coli, S. aureus and S. epidermidis in planktonic and sessile states. This post-functionalisation approach showed to be a promising strategy to prevent infections associated with medical devices. Chapter 4 follows a similar strategy, to achieve the functionalisation of a nanopatterned silicon nanowire surfaces with a commercially available and widely used biocide. In this chapter, we combined a high-aspect ratio surface nanotopography with the bactericidal effect of chlorhexidine against Escherichia coli and Staphylococcus aureus. These surfaces showed antimicrobial properties dependent on the initial concentration of biocide loaded, correlating the intrinsic resistance against chlorhexidine of the bacterial species used. We also investigated the impact of silicon nanowire arrays on the growth of E. coli and S. aureus sessile colonies. Our results suggested that the morphology of sessile bacterial communities was affected by the silicon nanowire arrays, paving the way for materials that can control microbial growth by engineering the surface nanotopography. Chapter 5 presents a novel approach to understand bacteria-surface interactions. In this work, we focused our attention on the attachment of E. coli cells to nonbactericidal porous aluminium oxide surfaces (pAlOx) . These surfaces presented a precisely defined porous nanotopography, which reduced attachment of bacteria up to 30-fold with respect to that of equivalent flat surfaces. In order to unravel the intensity of the metabolic processes undergoing after irreversible attachment, we studied the respiratory activity of bacteria attached to flat controls and pAlOx surfaces. Respiratory data analysis showed that bacteria attached to pAlOx displayed higher respiratory activity, suggesting that nanoporous surfaces may selectively favour attachment of bacteria with increased metabolism. Additionally, we proposed a theoretical model to describe the rates of attachment to and detachment from these surfaces, determining bacterial colonisation as a function of the surface topography, based on complementary experimental data. The novel approach introduced in this work may eventually serve as a platform to predict antibiofouling properties of surfaces emerging from bacteria-surface interactions.
Supervisor: Raval, Rasmita ; Diaz Fernandez, Y. A. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral