Waldman S D, Sacks M S, Lee J M
School of Biomedical Engineering, Dalhousie University, Halifax, NS, Canada, B3H 3J5.
Biomed Sci Instrum. 1999;35:51-6.
In a previous study, we have shown that the observed biaxial material behaviour of planar connective tissues is influenced by the sample gripping method. Commonly used suture attachments produced an apparently more compliant and extensible material compared to the same sample with clamped edges. We hypothesized that these differences were due to the imposed collagen fibre constraint under each method. In this study, we have directly compared the collagen fibre orientations which result under both gripping schemes. Small angle light scattering (SALS) was used to determine collagen fibre orientations in square bovine pericardial samples, before and after a 10% equibiaxial stretch. Local fibre distributions were determined at the sample centre and at the grip-sample interface. Resulting scattering patterns were statistically compared using repeated measures ANOVA. After stretch, collagen fibre distributions were identical at the sample centre where deformation is measured--but not at the sample boundaries. Therefore, the central fibre orientation distribution appears to be exclusively determined by the imposed deformation state. However, it is important to note that the loads necessary to achieve a given deformation depended strongly on gripping method. The resulting apparent differences in mechanical properties must be due to the method of load transmission. Indeed, fibres were observed to arc around suture attachment points, suggesting a discontinuous load transfer to the specimen which produced an apparent increase in extensibility and compliance. By contrast, only smooth transitions were observed at the clamped edges. Direct transmission of load from grip-to-grip in clamped samples (away from the sample centre) increased apparent stiffness.
在之前的一项研究中，我们已经表明，平面结缔组织观察到的双轴材料行为受样品夹持方法的影响。与边缘夹紧的相同样品相比，常用的缝线附着方式产生的材料明显更具柔顺性和可伸展性。我们推测这些差异是由于每种方法下施加的胶原纤维约束所致。在本研究中，我们直接比较了两种夹持方案下产生的胶原纤维取向。使用小角光散射（SALS）来确定方形牛心包样品在10%等双轴拉伸前后的胶原纤维取向。在样品中心和夹持-样品界面处确定局部纤维分布。使用重复测量方差分析对所得散射图案进行统计比较。拉伸后，在测量变形的样品中心处胶原纤维分布相同，但在样品边界处不同。因此，中心纤维取向分布似乎仅由施加的变形状态决定。然而，需要注意的是，实现给定变形所需的载荷强烈依赖于夹持方法。由此产生的力学性能上的明显差异必定归因于载荷传递方式。实际上，观察到纤维在缝线附着点周围呈弧形，这表明向样品的载荷传递是不连续的，并导致了可伸展性和柔顺性的明显增加。相比之下，在夹紧边缘处仅观察到平滑过渡。在夹紧样品中从一个夹具到另一个夹具的直接载荷传递（远离样品中心）增加了表观刚度。
