Tan Ting, Cholewa Nathan M, Case Scott W, De Vita Raffaella
Mechanics of Soft Biological Systems Laboratory, Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA, 24061, USA.
Materials Response Group, Department of Biomedical Engineering and Mechanics, Virginia Tech, Blacksburg, VA, 24061, USA.
Ann Biomed Eng. 2016 Nov;44(11):3225-3237. doi: 10.1007/s10439-016-1661-z. Epub 2016 Jun 2.
The uterosacral ligament and cardinal ligament (USL/CL) complex is the major suspensory tissue of the uterus, cervix, and vagina. This tissue is subjected primarily to bi-axial forces in-vivo that significantly alter its structure and dimension over time, compromising its support function and leading to pelvic floor disorders. In this study, we present the first rigorous characterization of the collagen fiber microstructure and creep properties of the swine USL/CL complex by using scanning electron microscopy and planar biaxial testing in combination with three-dimensional digital image correlation. Collagen fiber bundles were found to be arranged into layers. Although the fiber bundles were oriented in multiple directions, 80.8% of them were aligned within ±45[Formula: see text] to the main in-vivo loading direction. The straightness parameter, defined as the ratio of the end-to-end distance of a fiber bundle to its length, varied from 0.28 to 1.00, with 95.2% fiber bundles having a straightness parameter between 0.60 and 1.00. Under constant equi-biaxial loads of 2 and 4 N, the USL/CL complex exhibited significant creep both along the main in-vivo loading direction (the parallel direction) and along the direction perpendicular to it (the perpendicular direction). Specifically, over a 120-min period, the mean strain increased by 20-34[Formula: see text] in the parallel direction and 33-41[Formula: see text] in the perpendicular direction. However, there was no statistically significant difference in creep strains observed after 120 min between the parallel and perpendicular directions for either the 2 or 4 N load case. Creep proceeded slightly faster in the perpendicular direction under the equi-biaxial load of 2 N than under the equi-biaxial load of 4 N ([Formula: see text]). It proceeded significantly faster in the parallel direction under the equi-biaxial loads of 2 N than under the equi-biaxial loads of 4 N ([Formula: see text]). Overall, our findings contribute to a greater understanding of the biomaterial properties of the USL/CL complex that is needed for the development of new surgical reconstruction methods and mesh materials for pelvic floor disorders.
子宫骶韧带和主韧带（USL/CL）复合体是子宫、宫颈和阴道的主要悬吊组织。该组织在体内主要承受双轴力，随着时间的推移，这些力会显著改变其结构和尺寸，损害其支撑功能并导致盆底功能障碍。在本研究中，我们首次通过扫描电子显微镜、平面双轴测试以及三维数字图像相关技术，对猪USL/CL复合体的胶原纤维微观结构和蠕变特性进行了严格表征。发现胶原纤维束排列成层。尽管纤维束在多个方向上取向，但其中80.8%与体内主要加载方向的夹角在±45°以内。直线度参数定义为纤维束的端到端距离与其长度的比值，范围为0.28至1.00，95.2%的纤维束直线度参数在0.60至1.00之间。在2 N和4 N的恒定等双轴载荷下，USL/CL复合体在体内主要加载方向（平行方向）和与其垂直的方向（垂直方向）均表现出显著的蠕变。具体而言，在120分钟内，平行方向的平均应变增加了20 - 34°，垂直方向增加了33 - 41°。然而，对于2 N或4 N载荷情况，120分钟后平行方向和垂直方向观察到的蠕变应变在统计学上没有显著差异。在2 N的等双轴载荷下，垂直方向的蠕变比在4 N的等双轴载荷下略快（[公式：见原文]）。在2 N的等双轴载荷下，平行方向的蠕变比在4 N的等双轴载荷下显著更快（[公式：见原文]）。总体而言，我们的研究结果有助于更深入地了解USL/CL复合体的生物材料特性，这对于开发用于盆底功能障碍的新手术重建方法和网状材料是必要的。
