Aisa Rassoli - Biological Fluid Dynamics Laboratory, Biomechanics Department, Biomedical Engineering Faculty, Amirkabir University of Technology, Tehran, Iran
Nasser Fatouraee - Biological Fluid Dynamics Laboratory, Biomechanics Department, Biomedical Engineering Faculty, Amirkabir University of Technology, Tehran, Iran

Background: There is no consistent data on the mechanical properties of sheep intestine. OBJECTIVES: We performed a series of biaxial strain measurement experiments and extracted the constitutive model to describe the mechanical characteristics of the sheep intestinal tissue. METHODS: Eleven specimens were obtained freshly from sacrificed  sheep and the planar biaxial tests were performed on the tissue specimens by applying simultaneous loads along the circumfer-ential and longitudinal directions. Then the measured data were fitted into the anisotropic four-parameter Fung-type model and also to the modified Mooney-Rivlin model. RESULTS: The specimens showed some degree of anisotropy; the stiffer direction is not gener-ally predictable. Some of the specimens were stiffer in the circumferential direction, and the others in the longitudinal direction. However, the average results state the circumferential di-rection as the stiffer orientation. CONCLUSIONS: It can be concluded that sheep intestine be-haves normally as a nonlinear anisotropic tissue which is well-characterized by the modified Mooney-Rivlin model.

anisotropic constitutive model, fung-type model, nonlinear tissue, modify Mooney-Rivlin model, strain-energy function