Understanding the Effect of Foreign Particles on Membrane Elasticity in Lipid Vesicles

Phospholipid vesicles are excellent model systems for investigating the biophysical effect of various foreign particles on cell membranes. They are tunable self-assembled membrane structures that emulate real-life scenarios, and are thus useful to understand fundamental biophysical membrane properties and their pharmaceutical applications. Foreign particles can be ionic (salt), polymeric, or complex drug molecules. These particles interact with lipid membranes, affecting their nanoscopic structure and dynamics and simultaneously controlling their mesoscopic elastic properties. At salt concentrations identical to oceanic conditions experienced by marine life, we observed an increase in bending elasticity of model lipid membranes along with an increase in bilayer thickness. In the presence of short surfactant-like polymers, we observed the formation of multilayered structures and partial disruption of lipid bilayer causing a reduction in bending elasticity. However, for small drug molecules like Acetaminophen, quite often used as a common pain reliever, we observed an almost 50% reduction in membrane elasticity along with overall deformation of the vesicle structures. We have used a combination of neutron spin-echo (NSE), dynamic light scattering (DLS), small-angle scattering (SANS/SAXS), and cryo-TEM to bridge the gap between molecular lipid assemblies and their mesoscopic elastic properties. Our studies reveal new scaling behaviors to understand the vesicle dynamics with possible applications in topical drugs or nutraceutical formulations.