Sokolis Dimitrios P
Laboratory of Biomechanics, Center of Clinical, Experimental Surgery, and Translational Research, Biomedical Research Foundation of the Academy of Athens, 115 27 Athens, Greece.
Bioengineering (Basel). 2021 Feb 26;8(3):32. doi: 10.3390/bioengineering8030032.
Multiaxial testing of the small intestinal wall is critical for understanding its biomechanical properties and defining material models, but limited data and material models are available. The aim of the present study was to develop a microstructure-based material model for the small intestine and test whether there was a significant variation in the passive biomechanical properties along the length of the organ. Rat tissue was cut into eight segments that underwent inflation/extension testing, and their nonlinearly hyper-elastic and anisotropic response was characterized by a fiber-reinforced model. Extensive parametric analysis showed a non-significant contribution to the model of the isotropic matrix and circumferential-fiber family, leading also to severe over-parameterization. Such issues were not apparent with the reduced neo-Hookean and (axial and diagonal)-fiber family model, that provided equally accurate fitting results. Absence from the model of either the axial or diagonal-fiber families led to ill representations of the force- and pressure-diameter data, respectively. The primary direction of anisotropy, designated by the estimated orientation angle of diagonal-fiber families, was about 35° to the axial direction, corroborating prior microscopic observations of submucosal collagen-fiber orientation. The estimated model parameters varied across and within the duodenum, jejunum, and ileum, corroborating histologically assessed segmental differences in layer thicknesses.
小肠壁的多轴测试对于理解其生物力学特性和定义材料模型至关重要，但可用的数据和材料模型有限。本研究的目的是开发一种基于微观结构的小肠材料模型，并测试该器官沿长度方向的被动生物力学特性是否存在显著差异。将大鼠组织切成八段进行充气/拉伸测试，并用纤维增强模型表征其非线性超弹性和各向异性响应。广泛的参数分析表明，各向同性基质和周向纤维族对模型的贡献不显著，这也导致了严重的参数过度设定。对于简化的新胡克模型和（轴向和对角向）纤维族模型而言，这些问题并不明显，该模型提供了同样准确的拟合结果。从模型中去除轴向或对角向纤维族分别导致力-直径和压力-直径数据的不良表征。由对角向纤维族的估计取向角指定的各向异性主方向与轴向约成35°，这证实了先前对黏膜下胶原纤维取向的微观观察。估计的模型参数在十二指肠、空肠和回肠之间以及内部各不相同，这证实了组织学评估的各段层厚度差异。
