Interaction of lipid vesicles with nanoparticles and biomolecules : impacts on membrane organization, stability and phase behaviour

Abstract

Artificial lipid membranes mimic the cellular membranes, which are known to have a very complex structure. Lipid membranes can be conveniently designed in vitro using lipids which are arranged in a bilayer with a well-known and simpler composition, making them much easier to study. Thus, they serve as significant tools for understanding the physicochemical properties of cellular membranes. The usage of model membranes has been known since the early 1960s and they have been widely investigated to understand the physiological mechanisms and bio inspired applications. Lipid membranes are prone to fusion which is a fundamental process, but it limits their applications. Thus, in order to modify their structures and properties, they are often treated with external interactive species (nanoparticles, metal ions, biomolecules, polymers etc.). The modification of membrane surfaces by interfacial interactions can lead to the formation of better experimental models and develop new systems for biological applications. In particular, these interaction studies can be potentially used for the design and development of efficient drug delivery systems. The interactions of lipid membranes with external species can potentially induce changes in the properties and structures of the membranes which are important to analyze. These interactions can influence the fluidity and packing of the lipid membrane. Membrane properties are sensitive towards the presence of ions, small molecules, hydration, temperature and pH of the system. Even minor changes in the membrane structure and properties can have larger impacts on several important biological functions. As a result, the membrane interaction studies which affect the cellular processes account for the underlying mechanisms and the resultant influence at the nano-bio interface. Thus, a better understanding of the interactions is required which can help to bridge the gap between the lipid systems in vivo and in vitro at the membrane interface. Because of the immense importance of these systems, the lipid-based interactions and their applications have been of great interest in the recent past. Therefore, we have explored the interactions of different nanoparticles and biomolecules with lipid membrane vesicles (also known as liposomes). The systems studied in the thesis are lipid membrane vesicles, their assemblies with different nanoparticles (including carbon dots) and biomolecules (different amino acids). The possibility of lipid based system for the controlled release of an anticancer drug, Doxorubicin (DOX) was investigated. For the interaction studies, lipid bilayers of varying chain lengths, surface charges and phase transition temperatures were explored using the properties of a fluorescent membrane probe PRODAN with the help of different spectroscopic as well as imaging techniques.