Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland; Department of Obstetrics, University Hospital Zurich, 8091 Zurich, Switzerland.
Acta Biomater. 2015 Jan;11:314-23. doi: 10.1016/j.actbio.2014.09.012. Epub 2014 Sep 18.
Characterizing the mechanical response of the human amnion is essential to understand and to eventually prevent premature rupture of fetal membranes. In this study, a large set of macroscopic and microscopic mechanical tests have been carried out on fresh unfixed amnion to gain insight into the time-dependent material response and the underlying mechanisms. Creep and relaxation responses of amnion were characterized in macroscopic uniaxial tension, biaxial tension and inflation configurations. For the first time, these experiments were complemented by microstructural information from nonlinear laser scanning microscopy performed during in situ uniaxial relaxation tests. The amnion showed large tension reduction during relaxation and small inelastic strain accumulation in creep. The short-term relaxation response was related to a concomitant in-plane and out-of-plane contraction, and was dependent on the testing configuration. The microscopic investigation revealed a large volume reduction at the beginning, but no change of volume was measured long-term during relaxation. Tension-strain curves normalized with respect to the maximum strain were highly repeatable in all configurations and allowed the quantification of corresponding characteristic parameters. The present data indicate that dissipative behavior of human amnion is related to two mechanisms: (i) volume reduction due to water outflow (up to ∼20 s) and (ii) long-term dissipative behavior without macroscopic deformation and no systematic global reorientation of collagen fibers.
研究人类羊膜的力学响应对于理解并最终预防胎儿膜过早破裂至关重要。本研究对新鲜未固定的羊膜进行了大量的宏观和微观力学测试，以深入了解其时变材料响应和潜在机制。在宏观单轴拉伸、双轴拉伸和膨胀配置中，对羊膜的蠕变和松弛响应进行了表征。首次在原位单轴松弛测试中通过非线性激光扫描显微镜获得的微观结构信息对这些实验进行了补充。羊膜在松弛过程中表现出较大的张力减小和较小的粘弹性应变积累。短期松弛响应与伴随的面内和面外收缩有关，且取决于测试配置。微观研究表明，在开始时体积会大幅减小，但在松弛过程中长时间内体积没有变化。相对于最大应变归一化的拉伸-应变曲线在所有配置中都具有高度可重复性，并且可以量化相应的特征参数。目前的数据表明，人羊膜的耗散行为与两种机制有关：（i）由于水流出导致的体积减小（最长可达 20 秒）和（ii）无宏观变形和胶原纤维无系统全局重定向的长期耗散行为。
