Ji Fengting, Islam Mohammad R, Sebastian Frederick, He Xuehuan, Schilpp Hannah, Wang Bingrui, Hua Yi, Amini Rouzbeh, Sigal Ian A
Department of Ophthalmology, University of Pittsburgh, Pittsburgh, PA.
Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA.
bioRxiv. 2024 Sep 27:2024.09.12.612702. doi: 10.1101/2024.09.12.612702.
Because of the crucial role of collagen fibers on soft tissue mechanics, there is great interest in techniques to incorporate them in computational models. Recently we introduced a direct fiber modeling approach for sclera based on representing the long-interwoven fibers. Our method differs from the conventional continuum approach to modeling sclera that homogenizes the fibers and describes them as statistical distributions for each element. At large scale our method captured gross collagen fiber bundle architecture from histology and experimental intraocular pressure-induced deformations. At small scale, a direct fiber model of a sclera sample reproduced equi-biaxial experimental behavior from the literature. In this study our goal was a much more challenging task for the direct fiber modeling: to capture specimen-specific 3D fiber architecture and anisotropic mechanics of four sclera samples tested under equibiaxial and four non-equibiaxial loadings. Samples of sclera from three eyes were isolated and tested in five biaxial loadings following an approach previously reported. Using microstructural architecture from polarized light microscopy we then created specimen-specific direct fiber models. Model fiber orientations agreed well with the histological information (adjusted R2's>0.89). Through an inverse-fitting process we determined model characteristics, including specimen-specific fiber mechanical properties to match equibiaxial loading. Interestingly, the equibiaxial properties also reproduced all the non-equibiaxial behaviors. These results indicate that the direct fiber modeling method naturally accounted for tissue anisotropy within its fiber structure. Direct fiber modeling is therefore a promising approach to understand how macroscopic behavior arises from microstructure.
由于胶原纤维在软组织力学中起着关键作用，因此人们对将其纳入计算模型的技术非常感兴趣。最近，我们基于对长交织纤维的表示，引入了一种用于巩膜的直接纤维建模方法。我们的方法不同于传统的连续介质方法来对巩膜进行建模，传统方法将纤维均匀化并将其描述为每个单元的统计分布。在大尺度上，我们的方法从组织学和实验性眼内压诱导的变形中捕捉了粗大的胶原纤维束结构。在小尺度上，一个巩膜样本的直接纤维模型再现了文献中的等双轴实验行为。在本研究中，我们的目标对于直接纤维建模来说是一项更具挑战性的任务：捕捉在等双轴和四种非等双轴载荷下测试的四个巩膜样本的特定样本3D纤维结构和各向异性力学。从三只眼睛分离出巩膜样本，并按照先前报道的方法在五种双轴载荷下进行测试。然后，利用偏光显微镜下的微观结构，我们创建了特定样本的直接纤维模型。模型纤维方向与组织学信息吻合良好（调整后的R2>0.89）。通过反向拟合过程，我们确定了模型特征，包括特定样本的纤维力学性能以匹配等双轴载荷。有趣的是，等双轴特性也再现了所有非等双轴行为。这些结果表明，直接纤维建模方法在其纤维结构中自然地考虑了组织各向异性。因此，直接纤维建模是一种很有前途的方法，用于理解宏观行为是如何从微观结构中产生的。
