Lung surfactants and different contributions to thin film stability

Abstract

The surfactant lining the walls of the alveoli in the lungs increases pulmonary compliance and prevents collapse of the lung at the end of expiration. In premature born infants, surfactant deficiency causes problems, and lung surfactant replacements are instilled to facilitate breathing. These pulmonary surfactants, which form complex structured fluid-fluid interfaces, need to spread with great efficiency and once in the alveolus they have to form a thin stable film. In the present work, we investigate the mechanisms affecting the stability of surfactant-laden thin films during spreading, using drainage flows from a hemispherical dome. Three commercial lung surfactant replacements Survanta, Curosurf and Infasurf, along with the phospholipid dipalmitoylphosphatidylcholine (DPPC), are used. The surface of the dome can be covered with human alveolar epithelial cells and experiments are conducted at the physiological temperature. Drainage is slowed down due to the presence of all the different lung surfactant replacements and therefore the thin films show enhanced stability. However, a scaling analysis combined with visualization experiments demonstrates that different mechanisms are involved. For Curosurf and Infasurf, Marangoni stresses are essential to impart stability and interfacial shear rheology does not play a role, in agreement with what is observed for simple surfactants. Survanta, which was historically the first natural surfactant used, is rheologically active. For DPPC the dilatational properties play a role. Understanding these different modes of stabilization for natural surfactants can benefit the design of effective synthetic surfactant replacements for treating infant and adult respiratory disorders.

Interfacial rheology of coexisting solid and fluid monolayers

“…Uncertainties in the measurement of surface viscosity arise due to statistical variations in the magnetic moment, m , of the microbuttons, the temporal resolution in relating the optical image of the disk to the applied magnetic field, and errors in measuring the phase lag, γ While the 100 μmmicrobuttons are 2 – 10 times larger than the domains observed, the shear field induced by the microbutton motion extends for hundreds of microns containing hundreds of domains. Previousmonolayer rheological results using macroscopic wire rings (10 cm diameter ring, 0.7 mm diameter wires) (44, 56) and 2 mm diameter magnetic needles (2, 3, 43) showed similar trends with surface pressure or area fraction of solid domains (2, 3) and good quantitative agreement for similar monolayers.…”

Life and death of not so “bare” bubbles

“…This change is likely related to the rise of a surface stress due to the increased presence of surfactants at the interface. A more advanced model, in the spirit of the one developed by Hermans et al [27] for the drainage Figure 11: The sensitivity of bubbles to an external perturbation is tested by placing a small plastic obstacle next a bubble in continuous generation. Depending on the TTAB concentration, the bubble either (a) bursts when it touches the obstacle or (b) goes through it without damage.…”

Building Reconfigurable Devices Using Complex Liquid–Fluid Interfaces

“…Both of these processes have an energetic cost and, hence, determine the mechanical properties of the interface. Hermans et al described this intuitively using the expressionwhere, δ ij is the Kronecker delta and σ ij is the surface stress tensor (bold font corresponds to 2 × 2 tensors). The right‐hand side of Equation is broken into two terms that represent two different contributions to the surface stress.…”