A Two-Color mu-PIV/LIF System to Measure Unsteady Two-Phase Flow and Surfactant Transport Relevant to the Lung

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This project will develop and use an experimental technique to dynamically measure the microscale whole-field velocity, interfacial geometry and transport processes near the tip of a semi-infinite bubble propagating unsteadily through a surfactant-doped fluid-occluded tube. This experimental model of pulmonary airway reopening is relevant to acute respiratory distress syndrome (ARDS), which is characterized by pulmonary airway collapse and fluid occlusion. Subsequent airway reopening, driven by mechanical ventilation, generates damaging mechanical stresses on the airway walls that can result in ventilator-induced lung injury (VILI). We hypothesize that unsteady flows accompanied by dynamic surfactant transport may reduce wall stress and therefore the incidence of VILI. The microscale observations conducted in this study will provide us with a significant understanding of dynamic physicochemical interactions that can be manipulated to reduce the magnitudes of this damaging stimulus. The novelty of our proposed experimental approach stems from the use of a two-color fluorescent technique that simultaneous couples micro-particle image velocimetry (ì-PIV) and pulsed laser induced fluorescence (PLIV) to non-invasively measure convection fields, interfacial geometry and transport processes in time-dependent two-phase flows. Our technique will allow quantification of the flow field with 12.5ìm x 12.5ìm resolution ? this extraordinary detail will allow us to determine, for the first time, the dynamic stress field in the fluid phase in pulsatile flows. To do so, we will fluorescently label Infasurf (ONY, Inc), a pulmonary surfactant replacement used clinically, with â-BODIPY. The PLIV technology will allow us to simultaneously track the transport and deposition of the tagged surfactant in a time-dependent manner. The potential impact for this technology is widespread and significant. First, these capabilities will allow us to validate and expand upon our computational models of the lung in order to develop predictive models of airway reopening. Most importantly, these results will allow us to identify the relationship between the dynamic surface tension and surfactant transport interactions (including multi-layer creation and collapse) that can be exploited during mechanical ventilation to reduce deleterious mechanical stresses that can damage the lung. The technological advances afforded by the proposed research are important to engineering science because they allow for the quantification of micro-scale phenomena that have heretofore been inaccessible. In addition, the techniques have multi-disciplinary implications ? in addition to enhancing our understanding of pulmonary airway reopening, these new methodologies may be readily applied to gain fundamental insight into micro-fluidic devices in single or multi-phase flows, and therefore may find translation to lab-on-chip technologies. This project will provide expanded opportunities to a wide variety of students (undergraduates, graduate students and a post-doctoral researcher). Additionally, we will seek to recruit graduate students from historically underrepresented groups through associations with LS-LAMP and GAELA programs at Tulane University. We will partially support one post-doctoral researcher who will enhance his professional development through the mentoring of graduate students and undergraduate students.