Bircher Kevin, Ehret Alexander E, Spiess Deborah, Ehrbar Martin, Simões-Wüst Ana Paula, Ochsenbein-Kölble Nicole, Zimmermann Roland, Mazza Edoardo
ETH Zurich, Institute for Mechanical Systems, 8092 Zurich, Switzerland.
Empa, Swiss Federal Laboratories for Materials Science and Technology, 8600 Dübendorf, Switzerland.
Interface Focus. 2019 Oct 6;9(5):20190010. doi: 10.1098/rsfs.2019.0010. Epub 2019 Aug 16.
A series of mechanical experiments were performed to quantify the strength and fracture toughness of human amnion and chorion. The experiments were complemented with computational investigations using a 'hybrid' model that includes an explicit representation of the collagen fibre network of amnion. Despite its much smaller thickness, amnion is shown to be stiffer, stronger and tougher than chorion, and thus to determine the mechanical response of fetal membranes, with respect to both, deformation and fracture behaviour. Data from uniaxial tension and fracture tests were used to inform and validate the computational model, which was then applied to rationalize measurements of the tear resistance of tissue samples containing crack-like defects. Experiments and computations show that the strength of amnion is not significantly reduced by defects smaller than 1 mm, but the crack size induced by perforations for amniocentesis and fetal membrane suturing during fetal surgery might be larger than this value. In line with previous experimental observations, the computational model predicts a very narrow near field at the crack tip of amnion, due to localized fibre alignment and collagen compaction. This mechanism shields the tissue from the defect and strongly reduces the interaction of multiple adjacent cracks. These findings were confirmed through corresponding experiments, showing that no interaction is expected for multiple sutures for an inter-suture distance larger than 1 mm and 3 mm for amnion and chorion, respectively. The experimental procedures and numerical models applied in the present study might be used to optimize needle and/or staple dimensions and inter-suture distance, and thus to reduce the risk of iatrogenic preterm premature rupture of the membranes from amniocentesis, fetoscopic and open prenatal surgery.
进行了一系列力学实验，以量化人羊膜和绒毛膜的强度及断裂韧性。这些实验通过使用“混合”模型的计算研究得到补充，该模型明确表示了羊膜的胶原纤维网络。尽管羊膜厚度小得多，但它比绒毛膜更硬、更强且更坚韧，因此决定了胎膜在变形和断裂行为方面的力学响应。来自单轴拉伸和断裂试验的数据用于为计算模型提供信息并进行验证，然后该模型被用于合理化对含有裂纹状缺陷的组织样本抗撕裂性的测量。实验和计算表明，小于1毫米的缺陷不会显著降低羊膜的强度，但羊膜穿刺术和胎儿手术期间胎膜缝合造成的穿孔所引发的裂纹尺寸可能大于此值。与先前的实验观察结果一致，计算模型预测羊膜裂纹尖端附近的近场非常狭窄，这是由于纤维局部排列和胶原压实所致。这种机制使组织免受缺陷影响，并大大减少了多个相邻裂纹的相互作用。这些发现通过相应实验得到证实，结果表明，对于羊膜和绒毛膜，缝线间距分别大于1毫米和3毫米时，多条缝线之间预计不会相互作用。本研究中应用的实验程序和数值模型可用于优化针和/或吻合钉尺寸以及缝线间距，从而降低羊膜穿刺术、胎儿镜检查和开放性产前手术导致医源性胎膜早破的风险。
