Parra Elisa, Kinoshita Koji, Needham David
Center for Single Particle Science and Engineering (SPSE), Southern Denmark University , Campusvej 55, DK-5230 Odense, Denmark.
Department of Mechanical Engineering and Material Science, Duke University , Durham, North Carolina 90300, United States.
Langmuir. 2016 Oct 18;32(41):10570-10581. doi: 10.1021/acs.langmuir.6b01420. Epub 2016 Oct 3.
The present study is a microscopic interfacial characterization of a series of lung surfactant materials performed with the micropipette technique. The advantages of this technique include the measurement of equilibrium and dynamic surface tensions while acquiring structural and dynamic information at microscopic air-water interfaces in real time and upon compression. Here, we characterized a series of animal-derived and synthetic lung surfactant formulations, including native surfactant obtained from porcine lungs (NS); the commercial Curosurf, Infasurf, and Survanta; and a synthetic Super Mini-B (SMB)-containing formulation. It was observed that the presence of the natural hydrophobic proteins and, more strikingly, the peptide SMB, promoted vesicle condensation as thick membrane stacks beneath the interface. Only in the presence of SMB, these stacks underwent spontaneous structural transformations, consisting of the nucleation and growth of microtubes and in some cases their subsequent coiling into helices. The dimensions of these tubes (2-15 μm diameter) and their linear (2-3 μm/s) and volumetric growth rates (20-30 μm/s) were quantified, and no specific effects were found on them for increasing SMB concentrations from 0.1 to 4%. Nevertheless, a direct correlation between the number of tubes and SMB contents was found, suggesting that SMB molecules are the promoters of tube nucleation in these membranes. A detailed analysis of the tube formation process was performed following previous models for the growth of myelin figures, proposing a combined mechanism between dehydration-rehydration of the lipid bilayers and induction of mechanical defects by SMB that would act as nucleation sites for the tubes. The formation of tubes was also observed in Infasurf, and in NS only after subsequent expansion and compression but neither in the other clinical surfactants nor in protein-free preparations. Finally, the connection between this data and the observations from the lung surfactant literature concerning the widely reported "near-zero surface tension" for lung surfactant films and intact alveolar surfaces is also discussed.
本研究采用微量移液器技术对一系列肺表面活性剂材料进行了微观界面表征。该技术的优点包括测量平衡表面张力和动态表面张力，同时在微观气-水界面实时获取结构和动态信息以及压缩过程中的信息。在此，我们对一系列动物源性和合成肺表面活性剂制剂进行了表征，包括从猪肺中获得的天然表面活性剂（NS）；商业产品珂立苏、固尔苏和 Survanta；以及一种含合成超微迷你 B（SMB）的制剂。观察到天然疏水蛋白的存在，更显著的是肽 SMB 的存在，促进了囊泡凝聚，形成界面下方的厚膜堆叠。仅在 SMB 存在的情况下，这些堆叠会发生自发的结构转变，包括微管的成核和生长，在某些情况下随后会盘绕成螺旋状。对这些微管的尺寸（直径 2 - 15μm）及其线性生长速率（2 - 3μm/s）和体积生长速率（20 - 30μm/s）进行了量化，未发现 SMB 浓度从 0.1%增加到 4%对其有特定影响。然而，发现微管数量与 SMB 含量之间存在直接相关性，表明 SMB 分子是这些膜中微管成核的促进剂。根据先前关于髓鞘样结构生长的模型，对微管形成过程进行了详细分析，提出了脂质双层脱水-再水化与 SMB 诱导机械缺陷之间的联合机制，SMB 将作为微管的成核位点。在固尔苏中也观察到了微管的形成，在 NS 中仅在随后的扩张和压缩后观察到，而在其他临床表面活性剂或无蛋白制剂中均未观察到。最后，还讨论了这些数据与肺表面活性剂文献中关于肺表面活性剂膜和完整肺泡表面广泛报道的“接近零表面张力”的观察结果之间的联系。
