Development and characterisation of a molecularly tunable system for studying scale bridging of adhesive interactions

Abstract

Many phenomena concerning biological solid|liquid interfaces are driven and controlled by specific and unspecific bindings taking place between surfaces immersed in an electrolyte. More than half a century has already passed from the theoretical characterisation of soft materials and the first experiments on biological surfaces. Still, many questions are open as we miss an unambiguous approach that could link molecular interactions to macroscopic properties of interacting surfaces in complex environments such as physiologic fluids.In this thesis work, I present a novel strategy for systematically describing increasingly complex interfacial interactions of lipid membranes. This in particular includes competitive interactions of electrolyte ions and molecular adsorptions. We employ a bottom-to-top approach to define a model system which can well mimic natural membrane behaviours, and which can function as a starting point for introducing more complexity. Specifically, we tested a series of lipid molecules and developed a model systems that allows measurements with atomic force microscopy at the single molecule scale, and the surface forces apparatus at the macro molecular scale. We further integrated polymers with endgrafted chemical functionalities into the membranes with precise control and hence tuning of surface densities of functional groups. This allowed us to explore specific interactions of molecular functionalities with a charged surface in an electrolyte environment. This further unravelled nanoscopic competition between ions and molecules and together with thermodynamic analysis, a scaling from one to an Avogadro number of molecular interactions.As a result of this work, I further suggest new possible investigation paths and applications that start from the newly developed lipid based model systems now capable of high stability in extreme adhesive environment, conductivity for biosensing application and specific adaptability of their interface for fundamental science or medical/technological research.