[Liposomes of artificial surfactant and phase transition]

The respiratory distress syndrome in the new born is due to a deficiency of surfactant at the level of the gas-liquid interface of the pulmonary alveoli. Some recent treatments advocate the administration of artificial surfactant to mitigate this deficiency. In this article, the interfacial properties of sterile liposomes of the phospholipid surfactant were studied on a Langmuir balance film (isotherms of air-surface pressure II-A) during the course of compression-expansion cycles, simulating the respiratory cycles of compression-expansion cycles, simulating the respiratory cycles of inspiration-expiration. In the transition zone from the gel-crystal of liquid phospholipids, the isotherms issued from mixed liposomes show two pressure plateaux, which correspond to the collapse of the pure phases constituting them. In addition to their structural similarity with the sites of storing surfactant at the level of the lamellar bodies, the liposomes have the facility to act to the interface as an easily accessible reservoir and thus enable an artificial surfactant activity during the course of numerous respiratory cycles. The differences of behaviour at the interface of the liposomes with phospholipid films exposed with the aid of a volatile organic solvent, studied classically, explain themselves by preferential interface exchanges.