Relationships between surface viscosity, monolayer phase behavior, and the stability of lung surfactant monolayers

This chapter reviews how lipid chemistry and lateral organization in monolayers affect surface viscosity, how phase separation and more macroscopic organization influence the flow properties of monolayers, and the effects of lung surfactant specific proteins on the surface viscosity. The surface rheology of the clinical lung surfactants Survanta, Curosurf, and Infasurf is presented and correlated to the lipid and protein composition and phase behavior of these mixtures, and a new hypothesis on the optimal surface viscosity of a lung surfactant film is proposed. It could be that the necessary changes in surface viscosity in lung surfactant films arise from changes in monolayer phase behavior that occur with increasing surface pressure. Many phospholipids, including dipalmitoyl phosphatidylcholine (DPPC), have less‐ordered phases at low surface pressures, with short‐range molecular correlations. As the surface pressure increases to levels expected in the lungs, solid phases, with long‐range molecular correlations, forms.