Graduate Program in Biomedical Engineering, Department of Civil Engineering and Centre for Bioengineering Research and Education, The University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N1N4, Canada.
J Mech Behav Biomed Mater. 2011 Nov;4(8):1727-40. doi: 10.1016/j.jmbbm.2011.05.030. Epub 2011 May 30.
Capsule endoscopes are pill-size devices provided with a camera that capture images of the small intestine from inside the body after being ingested by a patient. The interaction between intestinal tissue and capsule endoscopes needs to be investigated to optimize capsule design while preventing tissue damage. To that purpose, a constitutive model that can reliably predict the mechanical response of the intestinal tissue under complex mechanical loading is required. This paper describes the development and numerical validation of a phenomenological constitutive model for the porcine duodenum, jejunum and ileum. Parameters characterizing the mechanical behavior of the material were estimated from planar biaxial test data, where intestinal tissue specimens were simultaneously loaded along the circumferential and longitudinal directions. Specimen-specific Fung constitutive models were able to accurately predict the planar stress-strain behavior of the tested samples under a wide range of loading conditions. To increase model generality, average anisotropic constitutive relationships were also generated for each tissue region by fitting average stress-strain curves to the Fung potential. Due to the observed variability in the direction of maximum stiffness, the average Fung models were less anisotropic than the specimen-specific models. Hence, average isotropic models in the Neo-Hookean and Mooney-Rivlin forms were attempted, but they could not adequately describe the degree of nonlinearity in the tissue. Values of the R2 for the nonlinear regressions were 0.17, 0.44 and 0.93 for the average Neo-Hookean, Mooney-Rivlin and Fung models, respectively. Average models were successfully implemented into FORTRAN routines and used to simulate capsule deployment with a finite element method analysis.
胶囊内窥镜是一种药丸大小的设备，配有一个摄像头，患者吞下后可以从体内拍摄小肠图像。为了优化胶囊设计同时防止组织损伤，需要研究肠道组织和胶囊内窥镜之间的相互作用。为此，需要开发一种能够可靠预测肠道组织在复杂机械载荷下的力学响应的本构模型。本文介绍了一种用于猪十二指肠、空肠和回肠的现象学本构模型的开发和数值验证。从平面双向拉伸试验数据中估计了表征材料力学行为的参数，其中同时沿环向和轴向加载肠道组织标本。Fung 本构模型能够准确预测在广泛的加载条件下测试样本的平面应力-应变行为。为了提高模型通用性，还通过将平均应力-应变曲线拟合到 Fung 势中，为每个组织区域生成了平均各向异性本构关系。由于最大刚度方向的可变性，平均 Fung 模型的各向异性小于特定于标本的模型。因此，尝试了Neo-Hookean 和 Mooney-Rivlin 形式的平均各向同性模型，但它们无法充分描述组织的非线性程度。非线性回归的 R2 值分别为 0.17、0.44 和 0.93，用于平均 Neo-Hookean、Mooney-Rivlin 和 Fung 模型。平均模型成功地实现到 FORTRAN 例程中，并用于通过有限元方法分析模拟胶囊展开。
