Visualization and Interfacial Microrhoelogy of Phospholipid Monolayers with and without Cholesterol

Phospholipid monolayers (with and without cholesterol) at the air-water interface serve as model systems for various biological interfaces, e.g. lung surfactant layers and outer leaflets of cell membranes. Although the dynamical (viscoelastic) properties of these interfaces may play a key role in stability, dynamics and function, the relatively weak rheological properties of most such monolayers have rendered their study difficult or impossible. Using a novel technique we have recently developed, we measure the viscoelastic properties of phospholipid monolayers, both with and without cholesterol, at the air-water interface. In particular, our measurements suggest remarkably long relaxation times (~0.1 sec.) Notably, our apparatus enable direct interfacial visualization during the measurement, which enables us to relate the observed interfacial structure and dynamics to the measured viscoelastic behavior. The influence of cholesterol upon these dynamic structures -- and thus rheology -- is visualized, measured and modelled.