Understanding Competitive Adsorption at the Air-Water Interface to Reverse Surfactant Inactivation in Acute Respiratory Distress Syndrome
Patrick C. Stenger, Jonathan G. Fernsler, and Joseph A. Zasadzinski. Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106
Lung surfactant adsorption to an air-water interface is strongly inhibited by the competitive adsorption of albumin or other surface-active serum proteins, and is likely the explanation of surfactant inactivation in Acute Respiratory Distress Syndrome (ARDS). In vitro, the addition of hydrophilic non-adsorbing polymers such as polyethylene glycol (PEG) and hyaluronic acid to the subphase restores the adsorption of lung surfactant to the interface, suggesting a promising therapy for ARDS. The rate of surfactant adsorption is quantitatively described using a variation of the classical Smolukowski analysis of colloid stability. Albumin adsorbed to the interface induces a steric and electrostatic energy barrier to surfactant diffusion of order 5 kBT: a reduction in adsorption equivalent to a 100 fold decrease in surfactant concentration. Hydrophilic polymers generate a depletion attraction between the surfactant aggregates and the interface that lowers the energy barrier. Surfactant adsorption increases exponentially with polymer concentration as predicted by the simple Asakura and Oosawa model of depletion attraction. Fluorescence microscopy images of the interface show distinct changes in morphology between albumin and surfactant-covered regions offering a visual confirmation of surfactant adsorption to the interface. The optimum molecular weight PEG for inactivation reversal is determined considering the scaling the depletion attraction and viscosity effects.