Contact-angle hysteresis induced by pulmonary surfactants

Hydrophilic surfaces in the form of glass slides have been coated with monolayers of three of the major components of pulmonary surfactant, and the wettabilities of the resulting surfaces have been studied by applying a single drop of saline. As fluid was added and removed over successive cycles, there was much hysteresis between the contact angle measured by a goniometer and the location of the triple point. All three surfactants, especially dipalmitoyl lecithin, were found to impart antiwetting properties, with maximum (advancing) contact angles sometimes exceeding 90 degrees and minimum (receding) contact angles seldom less than 28 degrees. In all cases (216 cycles on 36 films) fluid receded to expose the dry subphase. The hysteresis loops agree well with a similar loop calculated from published data for a cat lung in which the pressure-volume cycle has been established for both liquid and air inflation. Contact-angle hysteresis is offered as a possible alternative to surface tension as the surface parameter primarily responsible for the interfacial contribution to compliance hysteresis in the excised lung.