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

本项目将开发并使用一种实验技术来动态测量半无限气泡尖端附近的微尺度全场速度、界面几何形状和输运过程，这些气泡在表面活性剂掺杂的流体堵塞管中不稳定地传播。该实验模型与急性呼吸窘迫综合征（acute respiratory distress syndrome， ARDS）有关，ARDS以气道塌陷和液体闭塞为特征。随后气道重开，由机械通气驱动，对气道壁产生破坏性的机械应力，可导致呼吸机诱导的肺损伤（VILI）。我们假设非定常流动伴随着表面活性剂的动态输运可能会降低壁面应力，从而降低VILI的发生率。在本研究中进行的微尺度观察将为我们提供对动态物理化学相互作用的重要理解，可以通过操纵来减少这种破坏性刺激的大小。我们提出的实验方法的新颖性源于使用双色荧光技术，该技术同时耦合微粒子图像测速（ì-PIV）和脉冲激光诱导荧光（PLIV），以非侵入性地测量对流场，界面几何形状和随时间变化的两相流中的输运过程。我们的技术将允许以12.5ìm x 12.5ìm分辨率对流场进行量化。这一非凡的细节将使我们第一次能够确定脉动流中流体相的动态应力场。为此，我们将对临床使用的肺表面活性物质替代品Infasurf （ONY, Inc）进行荧光标记，标记为<s:1> - bodipy。PLIV技术将允许我们以时间依赖的方式同时跟踪标记表面活性剂的运输和沉积。这项技术的潜在影响是广泛而重大的。首先，这些功能将使我们能够验证和扩展我们的肺计算模型，以便开发气道重开的预测模型。最重要的是，这些结果将使我们能够确定动态表面张力和表面活性剂运输相互作用（包括多层产生和崩溃）之间的关系，这些相互作用可以在机械通气期间利用，以减少可能损害肺部的有害机械应力。所提出的研究提供的技术进步对工程科学很重要，因为它们允许对迄今为止无法达到的微观尺度现象进行量化。此外，这些技术具有多学科意义。除了增强我们对气道重开的理解外，这些新方法可以很容易地应用于对单相或多相流微流体装置的基本了解，因此可能会发现转化为芯片上的实验室技术。该项目将为各种各样的学生（本科生、研究生和博士后研究员）提供更多的机会。此外，我们将通过杜兰大学的LS-LAMP和GAELA项目，寻求从历史上代表性不足的群体中招募研究生。我们将部分支持一名博士后研究员，通过研究生和本科生的指导来加强他的专业发展。

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.