[Surface tension (surface tension factor) of the lungs].
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Animals↗
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Relations among alveolar surface tension, surface area, volume, and recoil pressure.
For pulmonary structure-function analysis excised rabbit lungs were fixed by vascular perfusion at six points on the pressure-volume (P-V) curve, i.e. at 40, 80, and 100% of total lung capacity (TLC) on inflation, at 80 and 40% TLC on deflation, and at 80% TLC on reinflation. Before fixation alveolar surface tensions (gamma) were measured in individual alveoli over the entire P-V loop, using an improved microdroplet method. A maximal gamma of approximately 30 mN/m was measured at TLC, which decreased during lung deflation to about 1 mN/m at 40% TLC. Surface tensions were considerably higher on the inflation limb starting from zero pressure than on the deflation limb (gamma-V hysteresis). In contrast, the corresponding alveolar surface area-volume (SA-V) relationship did not form a complete hysteresis over the entire volume range. There was a considerable difference in SA between lungs inflated to 40% TLC (1.49 +/- 0.11 m2) and lungs deflated to 40% TLC (2.19 +/- 0.21 m2), but at 80% TLC the values of SA were essentially the same regardless of the volume history. The data indicate that the gamma-SA hysteresis is only in part accountable for the P-V hysteresis and that the determinative factors of alveolar geometry change with lung volume. At low lung volumes airspace dimensions appear to be governed by an interplay between surface and tissue forces. At higher lung volumes the tissue forces become predominant.
Animals↗
Surface tension-surface area curves calculated from pressure-volume loops.
An energy analysis and data from the literature on the relation among surface area, recoil pressure, and lung volume are used to calculate the surface tension-surface area curves corresponding to pressure-volume loops. The energy analysis has been described earlier (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 50: 921-926, 1981). It is based on the assumption that the tissue structure of the lung constitutes a conservative mechanical system and hence that pressure-volume hysteresis is primarily a result of surface tension-surface area hysteresis. Unlike previous methods of calculating surface tension from recoil pressure, this method does not rely on the assumption that the tissue component of recoil in the air-filled lung is the same as recoil pressure of the saline-filled lung at the same lung volume. The calculated values of surface tension decrease to less than 2 dyn/cm as surface area decreases along the deflation limb of the pressure-volume curve. Surface tension increases very steeply with surface area on the inflation limbs, reaching a limiting value of just under 30 dyn/cm. The shape of the surface tension-surface area curves, unlike the shape of the curves calculated by previous methods, is similar to the shape obtained on surface tension balances for fluid extracted from lungs.
Animals↗
Intraocular tamponade and surface tension.
Surface tension is an important property of substances used as intraocular tamponades. The physical properties of currently available intraocular tamponades (gases, silicone oil and Healon) are compared with emphasis on surface tension. The gas/water interface surface tension is the greatest and therefore is the most effective in closing retinal breaks (70 erg/cm2). This is followed by silicone oil/water interface surface tension (50 erg/cm2). Healon is a 1% solution of water and therefore has no surface tension. Practical and theoretical considerations of various tamponades are described. Some properties of an ideal tamponade are suggested.
Gases↗
Tear film stability and tear surface tension.
Surface tension has been measured by the method of Ferguson and Kennedy on small (0.3-0.4 microliter) samples of tears from 65 normal and 35 dry eyes. Non-invasive break-up time (NIBUT) was also measured on the same patients as an indication of tear film stability. The mean (+/- SD) surface tension value was 43.6 +/- 2.7 mN/m for normals, and 49.6 +/- 2.2 mN/m for dry eyes. All NIBUT values for dry eyes were below 20 sec (8.9 +/- 5.1 sec, mean +/- SD, n = 35) while 53% of normal values were 30 sec or over. A negative correlation was found between surface tension and NIBUT for both dry eyes and normals. Comparison of surface tension results for tears and a variety of standard solutions indicated that mucus makes the greatest contribution, even at low concentrations, but the effect of proteins can be large, especially in inflammatory states where serum proteins leak from conjunctival vessels. The measurement of surface tension is simple and direct, and in conjunction with the NIBUT value can help in classification of tear quality in questionably dry eye cases.
Adolescent↗
Binary liquid mixtures. The relation between surface tension and surface composition as studied by MIES (metastable induced electron spectroscopy).
For a binary liquid mixture, we define the surface fraction of a component as the fraction of the surface which is covered by this species. The perfectly surface-sensitive electron spectroscopy MIES (metastable induced electron spectroscopy) allows to derive this quantity in a very direct manner from experiment with no model assumption needed. We find for several binary mixtures that the surface tension depends linearly on the surface fraction with striking accuracy. Even more surprising is the fact that for a system which deviates from this simple linear behavior the surface tension turns out to be a piecewise linear function of the surface fraction. Tentatively, we introduce as possible explanation the concept of phase separation within the surface layer. Further, we show that the surface molar fraction, i.e., the molar fraction within the top surface layer, deviates significantly from a linear or a piecewise linear relation to the surface tension.
Journal Article↗
Dynamic surface tension and surface rheology of biological liquids.
The paper presents results of dynamic and equilibrium surface tension measurements (using a maximum bubble pressure instrument) of serum and urine samples that were obtained from 80 healthy human of various sexes and ages. These data were compared with surface tension measurements of biological liquids obtained from patients suffering from malignant neoplasm of corpus uteri (n=5) and cervix uteri (n=31). In addition, surface dilatational rheology was determined on 32 samples using a drop shape method. The dilatational rheology data were compared with the dynamic surface tension data. Although some trends were found, no significant correlations exist between surface tension and rheology data and any of the disease states or stages. It is difficult to explain these findings in the framework of known mechanisms. However, our studies demonstrate that dynamic interface tensiometry of human biological liquids provide new insight into the biophysical behavior of these liquids, most likely reflecting compositional changes of them during ageing, the course of cancer and as a consequence of therapeutical interventions.
Journal Article↗
Effect of surface tension and surface elasticity of a fluid-fluid interface on the motion of a particle immersed near the interface.
The motion of a particle immersed in a fluid near a fluid-fluid interface is studied on the basis of the linearized Navier-Stokes equations. The motion is influenced by surface tension, dilatational surface elasticity modulus, and surface shear modulus, as well as by gravity. The backflow at the location of the particle after a sudden impulse has some universal features that are the same as for a rigid wall with stick boundary conditions. At short times the flow depends only on the mass densities of the two fluids. The nature of the short-time flow is calculated from potential flow theory. At a somewhat later time the particle shows a pronounced rebound. The maximum value of the rebound and the time at which the maximum occurs depend on the elastic properties of the interface.
Journal Article↗
Determination of the Surface tension of proteins. I. Surface tension of native serum proteins in aqueous media.
The desorption patterns of serum proteins in hydrophobic chromatography suggest that serum proteins that remain immersed in an aqueous medium and do not become in a protein-air interface are very hydrophilic. Contact angle measurements on fairly thick layers of hydrated serum proteins, formed on ultrafiltration membranes, yield surface tensions that correlate well with the degree of hydrophilicity derived from desorption data obtained by hydrophobic chromatography. For further confirmation the absorptivity of four human serum proteins was measured with respect to surfaces of different polymers of various surface tensions, for solution in aqueous solvents of different surface tensions. The surface tension of the solvent from which a dissolved protein adsorbs to precisely the same extent onto all solid substrates (regardless of their surface tensions) is equal to the surface tension of that protein. The surface tensions found by the contact angle (first value given) and by the protein adsorption methods (second value given) were. in erg/cm2; alpha 2-macroglobulin, 71.0, 71.0; serum albumin, 70.5, 70.2; immunoglobulin M, 69.5, 69.4; immunoglobulin G, 67.4, 67.7.
Adsorption↗
Determination of surface tensions of proteins. II. Surface tension of serum albumin, altered at the protein-air interface.
Serum albumin, which itself has a surface tension of congruent to 70.3 erg/cm2, when dissolved in water lowers the surface tension of water from 72.5 to congruent to 50 erg/cm2, as measured by a variety of means, including the pendant drop, the Wilhelmy plate and the platinum ring methods. Equally low and even lower surface tensions are found with the contact angle method, on a thin layer of albumin that had been adsorbed onto a low energy surface and subsequently exposed to air. Surface tensions of drops of albumin solutions varying in concentration from 0.01 to 5.5% (w/v) yielded, with a contact angle method, values that only varied between 67 and 61 erg/cm2. With the pendant drop, the Wilhelmy plate and the platinum ring methods, one essentially measures the surface tension at the air-liquid interface, at which proteins tend to adsorb, and where reversible or irreversible reorientation can be expected. The same holds for a thin layer of protein adsorbed onto a low energy surface, exposed to air. Thus, when through the very act of surface tension measurement, or after adsorbing protein onto a substrate, protein is exposed at the air-liquid interface, it apparently loses the pronounced hydrophilicity characteristic of its native hydrated state and manifests through reorientation a much more hydrophobic tertiary configuration.
Air↗
Experimental Study on Contact Angle Patterns: Liquid Surface Tensions Less Than Solid Surface Tensions.
The interpretation of contact angles in terms of solid surface tensions is not trivial. In the past, we and others have postulated that contact angles should be measured with liquid of surface tension larger than the anticipated solid surface tension, i.e., gamma(lv)>gamma(sv). This has recently been disputed. It is also not entirely obvious how to proceed experimentally since gamma(sv) is not known initially. Typically, one starts with a liquid of high gamma(lv) (such as water) and goes lower. We have stopped in the past when the contact angles became small. A question arises as to what would happen if we would go on. Contact angles of liquids with gamma(lv) less than or near gamma(sv) were measured on eight polymer-coated solid surfaces. The experimental contact angle patterns for gamma(lv) gamma(sv) were compared. Results suggest that contact angle interpretation in terms of solid surface tensions requires contact angles to be measured for gamma(lv)>gamma(sv) because the Young equation is not applicable for gamma(lv)<gamma(sv). Thus contact angle approaches that disregard this requirement are questionable. Copyright 2000 Academic Press.
Journal Article↗
Drug-Cyclodextrin Association Constants Determined by Surface Tension and Surface Pressure Measurements.
The complexation reaction between the amphiphilic peptide antibiotic polymyxin B and naturally occurring cyclodextrins, used as potential drug carriers, was quantitatively evaluated from surface tension measurements at various drug concentrations. The association constant, Ka, of polymyxin B:beta-cyclodextrin inclusion complex formation of 1:1 stoichiometry was determined from the change in the drug interfacial activity upon the addition of beta-cyclodextrin at the excess solution concentration (10(-3) M). The obtained Ka value is discussed in terms of molecular matching of the host cyclodextrin cavity and the guest drug molecule. Copyright 1999 Academic Press.
Journal Article↗
Effect of surface tension on alveolar surface area.
At fixed lung volume (VL), alterations in surface tension change alveolar surface area (S) and lung recoil (PL). Wilson (26), using data from fixed lungs (1, 9), quantified the isovolume change in S with PL. We reexamined this question in fresh excised rabbit lungs, with two important differences. First, we measured fractional changes in S by using diffuse light scattering, avoiding the potential upset of the balance of tissue and surface forces during fixation. Second, we altered surface tension by ventilating the lungs with nebulized polydimethylsiloxane, with much less residual fluid compared with lavage. We found that S decreased at low and mid VL (treatment surface tension > control) by about half of Wilson's estimates and was nearly unaffected by treatment at high VL. This suggests that with increased surface tension there is 1) greater septal retraction in lungs fixed by vascular perfusion compared with unfixed lungs and 2) a greater increase in PL and less loss of S than would have been predicted.
Animals↗
A method of measuring the surface tension and surface potential of lung surfactants.
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Action Potentials↗
Small phospholipid vesicles: internal pressure, surface tension, and surface free energy.
Tanford [Tanford, C. (1979) Proc. Natl. Acad. Sci. USA 76, 3318-3319] used thermodynamic arguments to show that the pressure difference across the bilayer of small phospholipid vesicles must be zero. This paper analyzes the implications of this conclusion in terms of Laplace's law and the basic thermodynamics of interfaces. In its usual form, Laplace's law is of questionable value for the vesicle. If the vesicle is in a state of metastable equilibrium, the surface free energy must be minimal with respect to several thermodynamic variables; the condition (delta F/ delta A) = 0 is not adequate by itself.
Biophysical Phenomena↗
Monitoring surfactant-induced hemolysis by surface tension measurement.
Surface tension measurements were employed to monitor the erythrocyte hemolysis process induced by surfactants. Two types of surfactants were used: the cationic surfactant DTAB and the anionic surfactant SDS. During DTAB-induced hemolysis, the changes in surface tension clearly demonstrate three stages. The first stage is characterized by surface tension increase, which is explained by surfactant removal from the suspending solution, due to adsorption onto cell membranes. In the second stage, surface tension remains constant, implying that equilibrium is attained between the membrane-bound surfactant and the surfactant in solution. The third stage is characterized by surface tension decrease that begins simultaneously with measurable cell-interior release, and lasts until hemolysis is completed. With SDS-induced hemolysis, the same three stages are observed at a low concentration; however, fluctuational increase in surface tension is obtained for higher concentrations. The latter is explained by additional adsorption of surfactant to solubilized membrane fragments.
Hemolysis↗
Drug-Cyclodextrin Association Constants Determined by Surface Tension and Surface Pressure Measurements.
The compression of water-insoluble drug monolayers spread on the aqueous subphase containing cyclodextrins (CD) led to a shift of surface pressure (pi)-area (A) isotherms toward smaller molecular areas with respect to the pi-A isotherms on the pure water subphase. The displacement of the compression isotherm obtained for the retinol spread on the beta-CD containing aqueous subphase was used to quantify the depletion process and to determine the drug-CD association constants. The proposed method appeared to be sensitive enough to account for extremely low amounts of sequestered drug molecules. The obtained values of the association constants Ka ranged from about 1.4.10(-2) to 36 m2/mol. The magnitudes of these constants are discussed in terms of drug bioavailability and of the stoichiometry of retinol-beta-cyclodextrin inclusion complex which was shown to have a 1:1 correspondence. Copyright 1999 Academic Press.
Journal Article↗
Some estimates of the surface tension of curved surfaces using density functional theory.
Density functional theory is used to calculate the surface tension of planar and slightly curved surfaces, which can be written as gamma(R)=gamma(infinity)(1-2delta(infinity)R), where R is the radius of curvature of the surface. Calculations are performed for a Lennard-Jones fluid, split into a hard-sphere repulsive potential and an attractive part. The repulsive part is treated using the local density approximation. The attractive part is treated using a high temperature approximation (HTA) in which the pair correlation function is approximated by the Percus-Yevick pair correlation function of a uniform hard-sphere fluid evaluated at a position-dependent average density. An expression relating the Tolman length delta(infinity) to the density profile of the planar surface is derived. Numerical results are presented for the planar surface tension gamma(infinity) and for delta(infinity) and are compared with those using mean field theory (MFT) and with those using the square-gradient approximation. Values for gamma(infinity) using the HTA are 30%-40% higher than those using MFT. Values for delta(infinity) using the HTA are around -0.1 (in units of the Lennard-Jones parameter sigma) and only weakly dependent on temperature. These values are less negative than the values from MFT. The square-gradient approximation gives reasonable estimates of the more accurate nonlocal results for both the MFT and the HTA.
Journal Article↗