Experimental and theoretical investigations of transport properties of DPPC monolayer

The paper deals with the analysis of dynamic behavior of a thin liquid film covered by an L-alpha-dipalmitoyl phosphatidylcholine (DPPC) monolayer during measurements carried out in a Langmuir film balance (LFB). This experimental device is often used for in vitro investigation of surface properties of lung surfactant (LS) and its components. A surface tension-area hysteresis loop measured during oscillations of interfacial area and an extremely low surface tension achieved under compression are the most spectacular features of the LS system. We believe that the presence of the monolayer strongly influences hydrodynamic phenomena in the liquid film in a way that enables a transport of floating or suspended fine solid particles (e.g., aerosol deposits) with the flow. This mechanism may contribute to alveolar clearance from insoluble aerosols. To find the velocity profile in the liquid layer a mathematical description of hydrodynamic processes was proposed and solved numerically. The results enabled us to determine the displacement of solid particles located on the interface, which was compared with experimental data from LFB. It was demonstrated that the surface tension gradient at the interface has an ordering effect on the flow in the system, and provides an apparent displacement of deposits. The theoretical model also adequately predicts the hysteresis loop, which can be measured in LFB. This investigation presents an indirect method of verification of the specific role of lung surfactant for alveolar clearance due to hydrodynamic transport.