Osmotic forces modify lipid membrane fluctuations.

Area of Science:

• Biophysics
• Soft Matter Physics
• Physical Chemistry

Background:

• Lipid bilayers are often modeled as impermeable, but permeability and osmotic forces significantly influence their behavior.
• The effects of fluid permeation on lipid membrane dynamics are not fully understood.

Purpose of the Study:

• To investigate the dynamics of a fluctuating, planar lipid membrane that allows fluid passage but not solute diffusion.
• To determine how membrane permeability affects relaxation modes and thermal undulations.

Main Methods:

• Theoretical modeling of a fluctuating, ideally selective lipid membrane.
• Analysis of membrane relaxation modes and their dependence on wavenumber and solute diffusion.

Main Results:

• The canonical membrane relaxation mode is restricted to a finite range of wavenumbers, dependent on solute diffusion rates.
• The equipartition result for membrane undulations is only valid within this restricted wavenumber range.
• Increased membrane surface tension shrinks this range, and above a critical tension, the relaxation mode vanishes.

Conclusions:

• Membrane permeability to fluid, while impermeable to solutes, fundamentally alters membrane dynamics.
• Experimental interpretations of membrane fluctuations, particularly in vesicles at moderate to high tensions, must account for these findings.