|Ph.D Student||Atia Lior|
|Subject||Equilibrium and Non-Equilibrium Configurations of|
Heterogeneous Biological Membranes
|Department||Department of Mechanical Engineering||Supervisor||Professor Josef Givli|
|Full Thesis text|
Lipid molecules in an aqueous solution spontaneously form a bilayer structure which has been firmly established as the universal basis of the cellular shell, A.K.A. the Biological Membrane (BM). We use 1D heterogeneous lipid bilayer structure as a model system to theoretically demonstrate a wide range of unique mechanochemical features of BMs. One of these major features is the composition dependent spontaneous curvature, which introduces a coupling between local shape and lipid composition in a BM system.
The first part of the dissertation introduces the concept of utilizing the coupling between shape and composition in BMs in order to use them as adaptive materials for applications at the micro-scale. We consider 1D BM structures and analyze their stable equilibrium configurations by calculating the first and second variations of the Gibbs free energy. Our numerical results demonstrate the richness of phenomena exhibited by these structures, and their potential applications. Specifically, we propose to utilize the unique properties and diverse functionality of BMs to provide sensing of temperature and osmotic pressure, as well as actuation in response to external stimuli. Besides the new and exciting possibilities they provide, a main advantage of the BMs is their bio-compatibility which makes them natural candidates for applications associated with invasive medical applications or study of biological systems. In addition, we show that one can take advantage of the adaptive nature of biological membranes in order to indirectly measure some of the non-standard material properties of the membrane.
The second part of this work relies on recent experimental studies which provide evidence for the existence of a spatially non-uniform temperature field in living cells and in particular in their plasma membrane. These findings have led to the development of a new and exciting field: thermal biology at the single-cell level. We examine theoretically a specific aspect of this field, i.e. how temperature gradients at the single cell level affect the phase behavior and geometry of heterogeneous membranes. We address this issue by utilizing the Onsager reciprocal relations to study the consequences and possible implications of the implied non-equilibrium thermodynamic configurations, by means of entropy variations relating thermal force to diffusive lipids flux. These Force-Flux relations enable us to formulate simplified non-linear dynamic equations for local shape and lipids composition. We demonstrate that even small temperature variations along the membrane may introduce intriguing phenomena, such as phase separation above the critical temperature and unusual shape response.