Surface rheological properties of the monolayer of synthetic lung surfactant

Abstract

The characteristics of synthetic lung surfactants with or without the surfactant proteins, SP-B, SP-C and SP-BC, were evaluated on the basis of surface modulus and viscosity obtained by applying the Maxwell model to the relaxation of the surface pressure produced by an area strain of 10% on a monolayer on the surface of a buffer solution and were compared with those of the synthetic lung surfactant TA developed earlier. The surface shear modulus and viscosity characteristic of the surface rheology for synthetic lung surfactant TA containing a trace of SP-BC showed a constant value for area strain of 10% under all equilibrium surface pressures and coincided with values of the mixed monolayers obtained by adding SP-BC and SP-B + C to the other components of lung surfactant (except surfactant proteins), but these moduli and viscosities for the systems without surfactant proteins increased with increase in equilibrium surface pressures. These results suggest that the existence of a trace of SP-BC in the synthetic lung surfactant TA improves its effectiveness and may serve as a ‘cushion’ among dipalmitoyl lecithin molecules in the monolayers during surface compression and expansion of these monolayers.