Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
Department of Structural Engineering, Norwegian University of Science and Technology, Trondheim, Norway.
Acta Biomater. 2022 Mar 15;141:244-254. doi: 10.1016/j.actbio.2022.01.003. Epub 2022 Jan 8.
Collagen fibers are the main load carrier in the mitral valve (MV) leaflets. Their orientation and dispersion are an important factor for the mechanical behavior. Most recent studies of collagen fibers in MVs lack either entire thickness study or high transmural resolution. The present study uses second harmonic generation (SHG) microscopy in combination with planar biaxial mechanical tests to better model and examine collagen fibers and mechanical properties of MV leaflets. SHG in combination with tissue clearing enables the collagen fibers to be examined through the entire thickness of the MV leaflets. Planar biaxial mechanical tests, on the other hand, enable the characterization of the mechanical tissue behavior, which is represented by a structural tissue model. Twelve porcine MV leaflets are examined. The SHG recording shows that the mean fiber angle for all samples varies on average by ±12° over the entire thickness and the collagen fiber dispersion changes strongly over the thickness. A constitutive model based on the generalized structure tensor approach is used for the associated tissue characterization. The model represents the tissue with three mechanical parameters plus the mean fiber direction and the dispersion, and predicts the biomechanical response of the leaflets with a good agreement (average r=0.94). It is found that the collagen structure can be represented by a mean direction and a dispersion with a single family of fibers despite the variation in the collagen fiber direction and the dispersion over the entire thickness of MV leaflets. STATEMENT OF SIGNIFICANCE: Despite its prominent role in the mechanical behavior of mitral valve (MV) leaflets, the collagen structure has not yet been investigated over the entire thickness with high transmural resolution. The present study quantifies the detailed through thickness collagen fiber structure and examines the effects of its variation on MV tissue modeling. This is important because the study evaluates the assumption that the collagen fibers can be modeled with a representative single fiber family despite the variation across the thickness. In addition, the current comprehensive data set paves the way for quantifying the disruption of collagen fibers in myxomatous MV leaflets associated with disrupted collagen fibers.
胶原纤维是二尖瓣 (MV) 瓣叶的主要承载结构。它们的取向和分散是机械行为的一个重要因素。最近大多数关于 MV 胶原纤维的研究要么缺乏整个厚度的研究，要么缺乏高穿壁分辨率。本研究采用二次谐波产生 (SHG) 显微镜结合平面双向力学试验，更好地模拟和研究 MV 瓣叶的胶原纤维和力学特性。SHG 与组织透明化相结合，可使胶原纤维在 MV 瓣叶的整个厚度范围内被检查。另一方面，平面双向力学试验使机械组织行为的特征化成为可能，这由结构组织模型来表示。对 12 个猪 MV 瓣叶进行了检查。SHG 记录显示，所有样本的平均纤维角度在整个厚度上平均变化±12°，胶原纤维分散在厚度上变化很大。基于广义结构张量方法的本构模型用于相关的组织特征化。该模型用三个力学参数加平均纤维方向和分散度来表示组织，并能很好地预测瓣叶的生物力学响应（平均 r=0.94）。结果发现，尽管 MV 瓣叶整个厚度上胶原纤维方向和分散度存在变化，但胶原结构可以用单一纤维家族的平均方向和分散度来表示。
尽管胶原在 MV 瓣叶的机械行为中起着重要作用，但它在整个厚度上的高穿壁分辨率仍未得到研究。本研究定量分析了整个厚度的详细胶原纤维结构，并研究了其变化对 MV 组织建模的影响。这很重要，因为该研究评估了这样一种假设，即尽管厚度上存在变化，但胶原纤维可以用具有代表性的单个纤维家族来建模。此外，当前的综合数据集为定量分析粘液样 MV 瓣叶中胶原纤维的破坏铺平了道路，粘液样 MV 瓣叶与胶原纤维的破坏有关。
