Amnion is a membrane that surrounds and structurally protects the developing fetus during pregnancy. The rupture of amniotic membranes prior to both normal and preterm deliveries involves stretch forces acting on a biochemically triggered weak zone of the membranes. Fracture toughness is an important mechanical property describing how the membranes containing a defect resist fracture, but this property has never been investigated in amniotic membranes. In this work, the fracture toughness of many samples cut from four pieces of amniotic membrane from different mothers was examined by uniaxial and pure shear (mode I) fracture tests. The measurement was checked for dependence on the sample geometry and notch length. Results from the uniaxial tensile test show J-shaped stress-strain curves and confirm that the amniotic membrane is a nonlinear material. The measured fracture toughness of four amniotic membranes ranged from 0.96 ± 0.11 to 1.83 ± 0.18 kJ m-2. Despite considering the effect of the presence of the defect on mechanical property measurement, similar fracture behaviour was observed for pre-notched and unnotched specimens, indicating that the membranes were extremely tolerant to defects. This defect-tolerant characteristic provides insight into the understanding of fetal membrane rupture.

中文翻译：

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人羊膜的断裂韧性。

羊膜是在怀孕期间围绕并在结构上保护发育中的胎儿的膜。正常和早产之前羊膜的破裂都牵涉作用于生物化学触发的膜弱区的拉伸力。断裂韧性是描述含有缺陷的膜如何抵抗断裂的重要机械性能，但是该性能从未在羊膜中研究过。在这项工作中，通过单轴和纯剪切（I型）断裂试验检查了从不同母亲的四块羊膜切下的许多样品的断裂韧性。检查测量结果是否取决于样品的几何形状和缺口长度。单轴拉伸试验的结果显示出J形应力应变曲线，并证实羊膜是非线性材料。测得的四种羊膜的断裂韧性为0.96±0.11至1.83±0.18 kJ m-2。尽管考虑了缺陷的存在对机械性能测量的影响，但对于预开槽和未开槽的样品，观察到了类似的断裂行为，表明该膜对缺陷的耐受性极强。这种耐缺损的特征提供了对胎儿胎膜破裂的了解。对于预开槽和未开槽的样品，观察到了类似的断裂行为，表明该膜对缺陷的耐受性极强。这种耐缺损的特征提供了对胎儿胎膜破裂的了解。对于预开槽和未开槽的样品，观察到了类似的断裂行为，表明该膜对缺陷的耐受性极强。这种耐缺损的特征为了解胎膜破裂提供了见识。