Department of Solid Mechanics, Royal Institute of Technology, Stockholm, Sweden.
Acta Biomater. 2012 Aug;8(8):3091-103. doi: 10.1016/j.actbio.2012.04.044. Epub 2012 May 11.
Collagen is the most abundant protein in mammals and provides the abdominal aortic aneurysm (AAA) wall with mechanical strength, stiffness and toughness. Specifically, the spatial orientation of collagen fibers in the wall has a major impact on its mechanical properties. Apart from valuable microhistological information, this data can be integrated by histomechanical constitutive models thought to improve biomechanical simulations, i.e. to improve the biomechanical rupture risk assessment of AAAs. Tissue samples (n = 24) from the AAA wall were harvested during elective AAA repair, fixated, embedded, sectioned and investigated by polarized light microscopy. The birefringent properties of collagen were reinforced by picrosirius red staining and the three-dimensional collagen fiber orientations were identified with a universal rotary stage. Two constitutive models for collagen fibers were used to integrate the identified structural information in a macroscopic AAA wall model. The collagen fiber orientation in the AAA wall was widely dispersed and could be captured by a Bingham distribution function (κ(1) = 11.6, κ(2) = 9.7). The dispersion was much larger in the tangential plane than in the cross-sectional plane, and no significant difference between the medial and adventitial layers could be identified. The layered directional organization of collagen in normal aortas was not evident in the AAA. The collagen organization identified, combined with constitutive descriptions of collagen fibers that depend on its orientation, explain the anisotropic (orthotropic) mechanical properties of the AAA wall. The mechanical properties of collagen fibers depend largely on their undulation, which is an important structural parameter that requires further experimental investigation.
胶原蛋白是哺乳动物中含量最丰富的蛋白质，为腹主动脉瘤（AAA）壁提供机械强度、硬度和韧性。具体来说，壁中胶原蛋白纤维的空间取向对其机械性能有重大影响。除了有价值的微观组织学信息外，这些数据可以通过组织力学本构模型进行整合，这些模型被认为可以改进生物力学模拟，即提高 AAA 的生物力学破裂风险评估。在选择性 AAA 修复期间，从 AAA 壁中采集了组织样本（n = 24），进行固定、嵌入、切片和偏光显微镜检查。用苦味酸天狼猩红染色增强胶原蛋白的双折射特性，并使用通用旋转台确定三维胶原蛋白纤维取向。使用两种胶原蛋白纤维本构模型将确定的结构信息整合到宏观 AAA 壁模型中。AAA 壁中的胶原蛋白纤维取向广泛分散，可以用 Bingham 分布函数（κ(1) = 11.6，κ(2) = 9.7）捕获。在切线平面中的分散性比在横截平面中大得多，并且无法确定中膜和外膜层之间的差异。在 AAA 中，正常主动脉中胶原的分层定向组织不明显。所确定的胶原组织与依赖其取向的胶原纤维本构描述相结合，解释了 AAA 壁的各向异性（正交各向异性）力学特性。胶原纤维的力学特性在很大程度上取决于其波动，这是一个重要的结构参数，需要进一步的实验研究。
