Yu Laura M Y, Lu James J, Chan Yawen W, Ng Amy, Zhang Ling, Hoorfar Mina, Policova Zdenka, Grundke Karina, Neumann A Wilhelm
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Rd., Toronto, ON, Canada M5S 3G8.
J Appl Physiol (1985). 2004 Aug;97(2):704-15. doi: 10.1152/japplphysiol.00089.2003. Epub 2004 Apr 2.
Existing methodology for surface tension measurements based on drop shapes suffers from the shortcoming that it is not capable to function at very low surface tension if the liquid dispersion is opaque, such as therapeutic lung surfactants at clinically relevant concentrations. The novel configuration proposed here removes the two big restrictions, i.e., the film leakage problem that is encountered with such methods as the pulsating bubble surfactometer as well as the pendant drop arrangement, and the problem of the opaqueness of the liquid, as in the original captive bubble arrangement. A sharp knife edge is the key design feature in the constrained sessile drop that avoids film leakage at low surface tension. The use of the constrained sessile drop configuration in conjunction with axisymmetric drop shape analysis to measure surface tension allows complete automation of the setup. Dynamic studies with lung surfactant can be performed readily by changing the volume of a sessile drop, and thus the surface area, by means of a motor-driven syringe. To illustrate the validity of using this configuration, experiments were performed using an exogenous lung surfactant preparation, bovine lipid extract surfactant (BLES) at 5.0 mg/ml. A comparison of results obtained for BLES at low concentration between the constrained sessile drop and captive bubble arrangement shows excellent agreement between the two approaches. When the surface area of the BLES film (0.5 mg/ml) was compressed by about the same amount in both systems, the minimum surface tensions attained were identical within the 95% confidence limits.
现有的基于液滴形状测量表面张力的方法存在一个缺点，即如果液体分散体是不透明的，例如临床相关浓度的治疗性肺表面活性剂，那么该方法在极低表面张力下无法发挥作用。本文提出的新型配置消除了两个重大限制，即脉动气泡表面张力仪以及悬滴装置等方法所遇到的薄膜泄漏问题，以及原始的俘获气泡装置中液体不透明的问题。锋利的刀刃是受限固着液滴的关键设计特征，可避免在低表面张力下薄膜泄漏。将受限固着液滴配置与轴对称液滴形状分析结合使用来测量表面张力，可实现装置的完全自动化。通过使用电动注射器改变固着液滴的体积，进而改变表面积，可轻松进行肺表面活性剂的动态研究。为了说明使用这种配置的有效性，使用了浓度为5.0 mg/ml的外源性肺表面活性剂制剂牛脂质提取物表面活性剂（BLES）进行实验。在受限固着液滴和俘获气泡装置之间对低浓度BLES获得的结果进行比较，表明两种方法之间具有极好的一致性。当两个系统中BLES薄膜（0.5 mg/ml）的表面积被压缩大约相同的量时，在95%置信限内达到的最小表面张力是相同的。
