Hadi Mohammad F, Barocas Victor H
Department of Biomedical Engineering, University of Minnesota, 312 Church Street SE, Minneapolis, MN 55455, USA.
J Biomech Eng. 2013 Feb;135(2):021026. doi: 10.1115/1.4023411.
A tissue's microstructure determines its failure properties at larger length scales, however, the specific relationship between microstructure and macroscopic failure in native and engineered soft tissues (such as capsular ligaments, aortic aneurysms, or vascular grafts) has proven elusive. In this study, variations in the microscale fiber alignment in collagen gel tissue analogs were modeled in order to understand their effects on macroscale damage and failure outcomes. The study employed a multiscale finite-element (FE) model for damage and failure in collagen-based materials. The model relied on microstructural representative volume elements (RVEs) that consisted of stochastically-generated networks of discrete type-I collagen fibers. Fiber alignment was varied within RVEs and between layers of RVEs in a macroscopic FE model of a notched dogbone geometry. The macroscale stretch and the microscale response of fibers for each of the differently aligned cases were compared as the dogbone was uniaxially extended to failure. Networks with greater fiber alignment parallel to the direction of extension failed at smaller strains (with a 6-22% reduction in the Green strain at failure), however, at greater grip forces (a 28-60% increase) than networks with fibers aligned perpendicular to the extension. Alternating layers of crisscrossed network alignments (aligned ±45 deg to the direction of extension) failed at smaller strains but at greater grip forces than those created using one fiber alignment type. In summary, variations in microscale structure via fiber alignment produced different macroscale failure trends. To conclude, these findings may be significant in the realm of tissue engineering and in soft tissue biomechanics.
组织的微观结构决定了其在较大长度尺度下的失效特性，然而，天然和工程化软组织（如囊韧带、主动脉瘤或血管移植物）的微观结构与宏观失效之间的具体关系一直难以捉摸。在本研究中，对胶原凝胶组织类似物中微观尺度纤维排列的变化进行了建模，以了解其对宏观损伤和失效结果的影响。该研究采用了基于胶原材料损伤和失效的多尺度有限元（FE）模型。该模型依赖于微观结构代表性体积单元（RVE），其由离散的I型胶原纤维的随机生成网络组成。在带缺口狗骨几何形状的宏观有限元模型中，纤维排列在RVE内部和RVE层之间变化。当狗骨单轴拉伸至失效时，比较了每种不同排列情况下的宏观拉伸和纤维的微观尺度响应。与延伸方向平行排列的纤维更多的网络在较小应变下失效（失效时格林应变降低6 - 22%），然而，与纤维垂直于延伸方向排列的网络相比，其所需的夹持力更大（增加28 - 60%）。交叉网络排列的交替层（与延伸方向成±45度排列）在较小应变下失效，但比使用一种纤维排列类型产生的网络需要更大的夹持力。总之，通过纤维排列的微观结构变化产生了不同的宏观失效趋势。综上所述，这些发现可能在组织工程和软组织生物力学领域具有重要意义。
