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Special Feature: Oral Presentations

PERFLUOROCARBON FLUID SURFACTANT INTERACTIONS: BIOPHYSICAL ASPECTS

Schürch, Samuel

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The purpose of this study was to investigate the interfacial properties, including film formation by adsorption, minimum surface tension upon film compression and film compressibility of pulmonary surfactant films, formed from therapeutic surfactants upon their exposure to various perfluorocarbon fluids (PFC). The Captive Bubble Surfactometer (CBS) has been modified to study surfactant films at the air-fluid as well as at the fluid-liquid interfaces. In addition to the captive air bubble, a sessile PFC drop is formed at the bottom of the bubble chamber. This modification of the set-up allows study of pulmonary surfactant films at the air bubble-liquid and at the PFC-liquid interfaces. The interfacial tension of the PFC drop can be changed by changing the fluid volume, whereas the surface tension of the captive air bubble is changed by varying the pressure inside the chamber. Thus, we were able to mimic surfactant films in partial and total liquid ventilation. The surfactants included the lipid extract preparations Curosurf, Survanta, and bovine lipid extract (BLES). The PFC included the fluids with relatively low vapor pressures, between ∼4 and 14 Torr, FC-43, perfluorodecalin, and perfluorooctylbromide, and those with relatively high vapor pressures, above 40 Torr, FC- 77(perfluorooctane) and FC- 75.The air bubble was either exposed to PFC prior to or after surfactant application. The spreadability of the PFCs on the surfactant films was evaluated by measuring the contact angle droplets of PFC formed on the films at their equilibrium surface tension of approximately 25mN/m. Results are shown in Table 1. The contact angles of FC- 43 or perfluorodecalin on a surfactant film at the equilibrium surface tension of ∼25 mN/m was ∼60° and that of FC-77, FC-75 or perfluorooctylbromide ∼30°. In contrast to the air-liquid surface tensions, the interfacial tensions of the surfactant films at the PFC- liquid interfaces reach minimum surface tensions of ∼1mN/m upon film compression.Near zero minimum surface tensions on repeated dynamic surfactant film compressions are achieved with lipid extract surfactants in combination with PFC fluids having relatively low vapour pressures at 37°C, such as FC-43, and perfluorodecalin, vapor pressures ∼4 and 14 Torr, respectively, but not with perfluorooctylbromide, vapor pressure ∼11 Torr. Perfluorooctyl- bromide and the fluids with relatively high vapor pressures (above 50 Torr) including FC-77 and FC-75, interfere with the surfactant film properties, as the minimum surface tensions are approximately 14 mN/m This value is far above the acceptable minimum surface tension (∼2mN/m) to stabilize the lung effectively. Low PFC spreadability on surfactant films is associated with the ability to achieve low minimum surface tensions on dynamic film compression, whereas high spreadability is associated with high minimum surface tensions of approximately 15 mN/m. Thus, in addition to vapor pressure, the spreadability of PFC fluids appears to be an important parameter to assess their compatibility with the lung surfactant film if partial liquid ventilation is considered.

Table 1
Table 1:
Minimum surface tension of materials tested

Supported by the CIHR, Canada, and the Alberta Heritage Foundation for Medical Research.)

Copyright © 2006 by the American Society for Artificial Internal Organs