Determining the physiological optimal surface viscosity

这项研究的主要目标是首次使用我们实验室独有的活跃的微观流变学技术来确定肺表面活性物质的生理最佳表面粘度。我们假设，在有效的肺表面活性物质中存在一个最佳的表面粘度，它既能快速吸附到空气-水界面，又能提供超低的表面张力。我们的目标是确定如何通过控制合成替代肺表面活性物质的胆固醇含量来最好地实现这一最佳效果。与宏观流变仪相比，我们的微观流变学技术的灵敏度提高了三个数量级，可以精确监控在胆固醇存在下肺表面活性物质膜的分子结构的变化，从而能够准确测量表面活性物质膜的表面粘度。最终，确定最佳胆固醇浓度将使合成表面活性物质能够更好地设计用于治疗新生儿呼吸窘迫综合征(NRDS)，并可能为成人呼吸窘迫综合征(ARDS)表面活性物质失活的原因提供见解。 我们假设小部分(1-5wt.%)的胆固醇减少了肺表面活性物质单层中饱和脂肪的结晶有序性，导致剪切粘度降低，从而增强了表面活性物质流动和覆盖肺泡界面的能力。我们还假设，过量的胆固醇(&gt；10wt%)通过增加界面膜的最小表面张力而降低肺表面活性物质在ARDS中的有效性。这种无法达到超低表面张力的现象被认为是薄膜界面能显著降低(线张力)的结果。低界面能会影响表面活性剂薄膜的机械内聚力，导致薄膜在压缩时失效，最终导致薄膜在较低的表面张力下变得不稳定。此外，脂质(胆固醇)-蛋白质的相互作用也可以通过改变它们在界面上的分子组织来改变这些机械和结构特性。通过测定生理和升高胆固醇存在下模型和临床相关表面活性物质膜的机械性能，我们可以了解胆固醇增加如何导致ARDS中表面活性物质失活，并确定更好的替代表面活性物质用于治疗。通过主动微观流变学技术确定的机械性能将与等温线、荧光显微镜和掠入射同步X射线衍射相关联，以确定胆固醇如何改变肺表面活性物质脂质的分子堆积，从而决定单分子层的机械性能。

The primary goal of this research is to determine, for the first time, the physiologically optimal surface viscosity of the lung surfactant using an active microrheology technique unique to our lab. We hypothesize that there exists an optimal surface viscosity in an effective lung surfactant that provides both rapid adsorption to the air-water interface and ultra-low surface tensions. Our goal is to determine how best to achieve this optimum by controlling the cholesterol fraction of a synthetic replacement lung surfactant. Three orders of magnitude increased sensitivity of our microrheology technique as compared to macroscopic rheometers allows precise monitoring of changes in the molecular organization of the lung surfactant film in the presence of cholesterol, enabling accurate measurements of surface viscosity of surfactant films. Ultimately, determining the optimal cholesterol concentration will enable a better design of synthetic surfactants to treat Neonatal Respiratory Distress Syndrome (NRDS) and may give insights into the causes of surfactant inactivation in Adult Respiratory Distress Syndrome (ARDS). We hypothesize that small fractions (1-5 wt. %) of cholesterol reduce the crystalline ordering of saturated lipids in lung surfactant monolayers, leading to a reduction in the shear viscosity, which enhances the surfactant's ability to flow and cover the alveolar interface. We also hypothesize that excess cholesterol ( >10 wt %) decreases the effectiveness of lung surfactants in ARDS by increasing the minimum surface tension of the interfacial film. This inability to reach ultra-low surface tensions is hypothesized to be a consequence of significantly reduced interfacial energy of the film (line tension). Low interfacial film energy can influence the mechanical cohesion in the surfactant film and lead to the failure of the film on compression, which ultimately causes the film to become unstable at lower surface tensions. Furthermore, lipid(cholesterol)- protein interactions can also alter these mechanical and structural properties by changing their molecular organization at the interface. By determining the mechanical properties of both model and clinically relevant surfactant film in the presence of physiological and elevated amounts of cholesterol, we can understand how increased cholesterol might lead to surfactant inactivation in ARDS and determine better replacement surfactants for treatment. The mechanical properties thus determined by the active microrheology technique will be correlated with isotherms, fluorescence microscopy, and grazing incidence synchrotron X-ray diffraction to determine how cholesterol alters the molecular packing of lung surfactant lipids, which determines the mechanical properties of monolayers.