RAPID IN-VITRO TESTS OF SURFACTANT FILM FORMATION - ADVANTAGES OF THEEXEROWA BLACK FILM METHOD

Based on our research, the natural configuration of surfactant from bi rth through adulthood takes the form of intraalveolar bubbles. Thus, b ubble film analysis would seem to be the specific in vitro testing met hod for lung surfactant. In the present study we report a battery of f ive in vitro tests for assessing structural and functional properties of surfactant bubbles and bubble films from hydrophobic extracts, name ly, the therapeutic surfactants Survanta (SU) and Infasurf (IN) (full strength and diluted to 3 mg phospholipid/mL) and from aqueous extract s from rabbit lung lavage at 3 mg phospholipid/mL (SAM). Each substrat e was assessed by: 1) Shake test: stable bubbles from SU, IN, and SAM (50/50, v/v in 95% ethanol) covered the peripheral surfaces, indicatin g positive response; bubble production by IN and SAM always exceeded S U; 2) Click test bubble clicking began immediately in all preparations except for undiluted SU, in which the onset of clicking was delayed m ore than 40 sec; 3) Pattle's stability test: diameters of SU, IN, and SAM bubbles were unchanged for more than 20 min in aerated solution, i ndicating stable very low surface tension; 4) bubble generation by gas dispersion from a single capillary: full-strength concentration of SU and IN produced relatively large bubbles-bubble rate (number/ min) an d size were comparable; all SU bubbles rupture in <25 min, whereas IN bubbles were stable for >30 min; and 5) Exerowa black film method: in contrast with each of the preceding methods for studying intact bubble s, the Exerowa method focuses on the contact between bubble films and permits direct observation of film formation and determination of film structure. Stable black films were formed spontaneously by both IN (f ull strength and diluted) and SAM. Conversely, SU (full strength) form ed no black films but stable rheological films. Diluted SU films ruptu red in 50% of trials. Since methods 1, 2, and 3 were nondiscriminatory and method 4 produced unphysiologically large bubbles for most mammal s, we concluded that the black film method of Exerowa is the most disc riminating of the tests studied here. It provides a unique visual reco rd of foam film formation and stability and clearly defines difference s relative to both the nature and concentration of the preparations. ( C) 1996 Wiley-Liss, Inc.