Thermodynamics of Inter-Leaflet Cavitation in Lipid Bilayer Membranes

Abstract

Inter-leaflet cavitation in lipid bilayer membranes or shortly, intra-membrane cavitation (IMC) is a formation of gas bubbles between the two leaflets of the membrane. The present paper focuses on the thermodynamics of IMC, namely on the minimum work required to form such an intra-membrane cavity. The minimum work can be separated into two terms, one that is dependent on the volume and number of gas molecules in the bubble and the second that depends on the volume and bubble geometry. Minimizing the second term for a given volume determines the optimized bubble shape. In homogeneous cavitation this term is proportional to the bubble surface area and, therefore, the bubble is spherical. In contrast, in IMC the second term is no more a simple function of the bubble area and the optimized cavity is not spherical because of the finite elasticity of the membrane. Using a simplified geometry assumption, the second term is derived and minimized. It was found that the optimized cavity is almost spherical at large bubble volumes, while at small volumes the cavity has a lens-like shape. The optimized shape is used to analyze the minimum work of IMC.