A recent study in South Africa has confirmed, for the first time, that a vaginal gel formulation of the antiretroviral drug Tenofovir, when applied topically, significantly inhibits sexual HIV transmission to women [10]. However the gel for this drug, and anti-HIV microbicide gels in general, have not been designed using full understanding of how gel spreading and retention in the vagina govern successful drug delivery. Elastohydrodynamic lubrication theory can be applied to model such spreading of microbicide gels, which are inherently non-Newtonian [13], [15]. A yield stress is emerging as one of the important properties of microbicide gel vehicle deployment, as this may improve retention within the vaginal canal. On the other hand, a yield stress may decrease the initial extent of the coating flow. Here, we first explain a certain yield stress paradox observed generally in many lubrication flows. Four conditions are determined, via scaling analysis, which mitigate the inconsistency in the use of lubrication theory to analyze the specific problem of elastic wall squeezing flow of yield stress fluid. Parameters characterizing these conditions are obtained experimentally for a test gel. Using them, it is shown that the lubrication approximation may be applied to the elastic wall-squeezing problem for this gel.

最近在南非进行的一项研究首次证实，抗逆转录病毒药物替诺福韦的阴道凝胶制剂在局部应用时可显着抑制 HIV 向女性的性传播 [10]。然而，这种药物的凝胶以及一般的抗 HIV 杀微生物剂凝胶的设计尚未充分了解凝胶在阴道中的扩散和保留如何控制成功的药物递送。弹性流体动力润滑理论可用于模拟杀微生物剂凝胶的这种扩散，这些凝胶本质上是非牛顿的 [13]、[15]。屈服应力正在成为杀菌剂凝胶载体部署的重要特性之一，因为这可能会改善阴道管内的保留。另一方面，屈服应力可能会降低涂层流动的初始范围。这里，我们首先解释在许多润滑流中普遍观察到的某个屈服应力悖论。通过标度分析确定了四个条件，减少了使用润滑理论分析屈服应力流体弹性壁挤压流动的具体问题时的不一致性。对于测试凝胶，通过实验获得表征这些条件的参数。使用它们，表明润滑近似可以应用于这种凝胶的弹性壁挤压问题。