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Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118
Airway reopening mechanics depend on surfactant
physicochemical properties. During reopening, the progression of a
finger of air down an airway creates an interface that is continually expanding into the bulk fluid. Conventional surfactometers are not
capable of evaluating physicochemical behavior under these conditions.
To study these aspects, we investigated the pressure required to push a
semi-infinite bubble of air down a fluid-filled cylindrical capillary
of radius R. The ionic surfactant SDS
and pulmonary surfactant analogs
L-
-dipalmitoylphosphatidylcholine and Infasurf were investigated. We found that the nonequilibrium adsorption of surfactant can create a large nonequilibrium normal stress and a surface shear stress (Marangoni stress) that increase the
bubble pressure. The nonphysiological surfactant SDS is capable of
eliminating the normal stress and partially reducing the Marangoni stress. The main component of pulmonary surfactant,
L-
-dipalmitoylphosphatidylcholine, is not capable of reducing either stress, demonstrating slow adsorption properties. The clinically relevant surfactant Infasurf is shown to
have intermediate adsorption properties, such that the nonequilibrium normal stress is reduced but the Marangoni stress remains large. Infasurf's behavior suggests that an optimal surfactant solution will
have sorption properties that are fast enough to reduce the reopening
pressure that may damage airway wall epithelial cells but slow enough
to maintain the Marangoni stress that enhances airway stability.
airway closure; dynamic surface tension; L-
-dipalmitoylphosphatidylcholine; Infasurf; Marangoni stress
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