Collaborative Research: Effects of interfacial viscosities on flow of lung surfactants

更广泛的影响和背景：正常肺部的液体衬里被表面活性剂覆盖。液体衬里对于氧气的摄入和二氧化碳的排出是必不可少的，然而，如果没有这些表面活性剂这种降低表面张力的材料，呼吸就会变得非常困难。除了降低表面张力以尽量减少呼吸的工作量外，肺表面活性剂还在呼吸循环中改变表面张力，以保护肺泡在呼气时不塌陷，在吸气时不过度扩张。缺乏功能性表面活性剂会导致呼吸窘迫综合征，这是一种对成年人和早产儿都可能致命的疾病。肺表面活性剂替代疗法已经在降低早产儿死亡率方面取得了重大进展，但进一步的改善可以从对相关界面流体动力学的更好理解中获益。目前的肺表面活性剂流体动力学模型忽略了表面粘度，这可能是一个重要的贡献。有必要了解表面粘度在肺表面活性剂中的作用，因为在小尺度上，如肺泡内壁的液体，表面粘度的相对影响与表面张力的相对影响相当。自然和人工材料的运动，降低肺液体衬里的表面张力将被研究。利用先进的计算机模型和最近发展的实验技术，将检查肺表面活性剂的主要成分DPPC（双棕榈酰磷脂酰胆碱）的行为。我们将详细研究最近发现的dppc覆盖的液体层的各种流动特性。拟议的项目不同于以往的研究，因为它弥合了两个极端之间的巨大鸿沟：(i)纯理论方法，假设没有与肺表面活性剂相关的固有界面粘度；（ii）纯经验方法，使用特设方程来解释实验观察到的肺表面活性剂的反应。目前，绝大多数肺表面活性剂的研究都属于这两个阵营中的一个。前者缺乏解释真实肺表面活性剂行为的许多方面的能力，后者缺乏预测给定表面活性剂对不同流动条件的反应的能力。在模拟表面活性剂体系（如DPPC）中界面粘度的测量和建模方面的改进，可能有助于人们更好地理解天然肺表面活性剂的功能。所开发的功能可随后用于多组分肺表面活性剂系统。最终，这个项目的结果可能有助于加速开发更有效的治疗方法。多学科团队（来自机械工程和数学），凭借其富有成效的合作记录，将为研究生和本科生提供界面流体力学教育的绝佳机会。知识价值。该项目将开发一种结合实验和计算的协同能力，以解释与DPPC相关的一级界面粘弹性流体动力学，描绘其各种流动状态。到目前为止，磷脂DPPC是肺表面活性剂中最普遍的成分，占肺表面活性剂质量的55.60%。这种高度亲两性的分子有一个亲水的极性头和一对疏水的尾部，使它基本上不溶于水。将测量其平衡界面性质，并将其纳入考虑表面变形，界面加速度和时空表面活性剂浓度的预测模型。该模型将直接针对典型流动的实验进行测试，在界面区域具有大的随时间变化，然后用于预测太小的尺度上的动力学，无法进行实验测量。这将提供一个急需改进的理解和建模的固有界面特性，包括由于表面张力梯度，表面剪切和膨胀粘度，以及界面和体流之间的粘性耦合的弹性效应。

Lopez, Juan M.CBET-1064498Broader Impact and Background: The liquid lining of normal lungs is covered by surfactants. The liquid lining is essential for oxygen intake and carbon dioxide output, however without these surface-tension-reducing materials, known as surfactants, breathing would be laborious if not impossible. Aside from reducing the surface tension to minimize the work of breathing, lung surfactants also vary the surface tensionduring the breathing cycle in order to protect the alveoli against collapse on exhalation and over-expansion upon inhalation. A lack of functioning surfactants leads to respiratory distress syndrome, a potentially fatal condition in both adults and premature infants. Replacement lung surfactant therapy has already made major inroads in reducing the mortality rate amongst pre-term infants, but further improve-ments can benefit from a better understanding of the associated interfacial hydrodynamics. Present models of lung surfactant hydrodynamics neglect surface viscosities, which may make a significant contribution. There is a need to understand the role of surface viscosities in lung surfactants because at small scales, such as those of the liquid lining the alveoli, the relative effects of surface viscosities are comparable to that of surface tension. The movement of natural and artificial materials that reduce the surface tension of the liquid lining of lungs will be studied. Using advanced computer models and recently developed experimental techniques, the behavior of DPPC (dipalmitoyl phosphatidylcholine), the primary constituent of lung surfactant, will be examined. Various flow characteristics of DPPC-covered liquid layers, that have recently been revealed, will be examined in detail. The proposed project differs from previous studies in that it bridges the vast divide between the two extremes of (i) purely theoretical approaches that assume no intrinsic interfacial viscosities associated with lung surfactants and (ii) purely empirical approaches that use ad hoc equations to explain experimentally observed responses of lung surfactants. Presently, the vast majority of lung surfactant research falls into one or the other of these two camps. The former lack the ability to explain many aspects of how real lung surfactants behave and the latter lack the ability to predict how a given surfactant will respond to a different set of flow conditions.Improvements in measurement and modeling of interfacial viscosities in model surfactant systems, such as DPPC, may help one to understand better the functioning of natural lung surfactants. The capabilities developed can be subsequently used for multi-component lung surfactant systems. Ultimately, the results of this project may help speed up the development of more effective therapies. The multidisciplinary team (from mechanical engineering and mathematics), with its proven track record of productive collaboration, will provide an excellent opportunity to educate graduate and undergraduate students in interfacial hydrodynamics.Intellectual Merit. The project will develop a synergistic capability incorporating experiments and computations to account for the leading order interfacial viscoelastic hydrodynamics associated with DPPC, delineating its various flow regimes. By far, the phospholipid DPPC is the most prevalent component of lung surfactants, constituting 55{60% of lung surfactant by mass. This highly amphiphilic molecule has a hydrophilic polar head and twin hydrophobic tails, making it essentially insoluble in water. Its equilibrium interfacial properties will be measured and incorporated into a predictive model taking into account surface deformation, interfacial acceleration and spatio-temporal surface surfactant concentration. The model will be tested directly against experiments for a canonical flow with large time-dependent changes in the interfacial area, and then used to predict the dynamics at scales too small for experimental measurements. This will provide a much-needed improved understanding and modeling of the intrinsic interfacial properties, including the elastic effects due to surface tension gradients, surface shear and dilatational viscosities, and the viscous coupling between the interfacial and bulk flows.