Surfactant liquid and black foam film formation and stability in vitro and correlative conditions in vivo

Abstract

We studied foam film formation by three preparations that are used as surfactant replacement therapy by injection into the lungs of neonatal infants with surfactant insufficiency (“respiratory distress syndrome”). The preparations contain either all putative hydrophobic components of the normal surfactant system (prepared from bovine lung lavage, Infasurf (IN); prepared from minced bovine lung tissue, Survanta (SU)) or a single component of the system, dipalmitoylphosphatidylcholine (Exosurf Neonatal (EX)). Foam film formation is relevant directly to normal surfactant structure and function in vivo in the neonatal period (Pediatr. Res. 12 (1978) 1070–1076). We assessed morphology and stability of liquid to black film formation and its dependence on substrate concentration C, adsorption time, temperature T, “capillary pressure” P c, film drainage time τ 0–1 and black film formation times τ 1–2. We found that (1) in contrast with the other preparations, IN regularly formed stable black films at the lowest C (“threshold C” C t) under all conditions of T (22 and 37°C) and P c (0.3, 0.4, 1.2 and 2.4 × 10 3 dyn cm −2), (2) EX also formed black films but differed from IN in that C t was higher, film integrity required a longer adsorption time and black film formation was blocked (instability) at P c values of 1.2 and 2.4 × 10 3 dyn cm −2 and (3) SU did not form black films but instead formed slowly (long τ 0–1 and τ 1–2), at relatively high C t, viscosity-dependent inhomogeneous atypical (“rheological”) films containing aggregates of material in the preparation. Extrapolation to in-vivo conditions of C, T and P c indicates that both IN and SU (but not EX) may form stable foam films in situ, that film formation by IN is the more efficient process and that stable surfactant foam films, formed naturally in vivo, are consistent with both the in-vitro characteristics described here and correlative lung function in vivo.