A critical assessment of the Wilhelmy method in studying lung surfactants.

Abstract

SUMMARY1. The surface properties of over 250 films of dipalmitoyl lecithin (DPL) and Tween 20 on distilled water have been investigated using two different surface balances simultaneously, the Wilhelmy balance, popular in physiological studies, and the Du Nuoy ring method whose readings are independent of contact angle.2. Using concentrations of DPL ranging from 0-08 to 1 90/tg cm-2 on a Langmuir trough where the pool area was cycled from 100 to 27 5 % of maximum, the Wilhelmy balance registered virtually the same force per wetted perimeter as the ring method for both pure water and Tween 20, but appreciably lower values for DPL over the whole cycle.3. The above differences can be explained on the basis of a significant (45-70O) contact angle, a surface property also demonstrated photographically and by direct measurement.4. Contact angle was shown to vary with pool area, a relationship exhibiting hysteresis.5. This study indicates that the Wilhelmy balance has been an unfortunate choice of instrument for studying DPL films whose surface tensions are appreciably higher than previously estimated.

Surface tension induced by dipalmitoyl lecithin in vitro under physiological conditions

“…One other possibility involves the contact angle observed at the surface of the Wilhelmy flag when making no effort to follow physiological conditions comprehensively (Barrow & Hills, 1979). This could partially explain the unduly low readings recorded in earlier work.…”

“…It is difficult to determine which parameter or set of conditions are responsible for the differences from previous studies using the Wilhelmy balance since this would involve varying some twenty-eight possible combinations. One other possibility involves the contact angle observed at the surface of the Wilhelmy flag when making no effort to follow physiological conditions comprehensively (Barrow & Hills, 1979). This could partially explain the unduly low readings recorded in earlier work.…”

Role of Lipid Polymorphism in Pulmonary Surfactant

“…U p o n compression at 22"C, t h e iiloilolayer achieved a H value near 5 0 mN/m ( y that y must be near zero was required to explain the classical alveolar cointinuous liquid lining theory, n~h i c h is now disputed(15). Most recent alveolar models d o inot invoke a continuous liquid lining, and the ability of the ~Yiillnelm~ plate method t o revort low ~a l -, ues of y has beein questioned(16). Given these concerns, we could not rule out the possibility t h a t our formulations would filtnctioin well in vivo Ithe minimum v…”

Water repellency induced by pulmonary surfactants.

“…This mechanism is largely theoretical speculation based upon the finding that the predominant surfactant identified in the lung (Brown, 1964) is dipalmitoyl lecithin (DPL) and this can induce a contact angle (Hills & Ng, 1974;Barrow & Hills, 1979a) which has also been observed at the surface of excised pulmonary epithelium (Hills & Barrow, 1979). In surface physics (Adamson, 1967), a contact angle is the hallmark of non-wetting, and agents which impart this property to otherwise hydrophilic surfaces have many industrial applications of which one of the most common is imparting water repellency to hydrophilic sub-phases such as cotton.…”