Shear Modulus of the Partially Obstructed Rat Small Intestine

A number of factors influence gastrointestinal tissue structure and mechanical properties such as the physical environment and diseases like partial obstruction. Hence multi-axial biomechanical properties are important for understanding the pathophysiology of the obstructed intestine. The aim was to estimate the multi-axial biomechanical properties, in particular with focus on the shear modulus. Partial obstruction of mid-jejunum was created surgically by placement of a polyethylene ring for two weeks in seven male rats. Sham operation was made in five other rats. At the time for termination, three 6-cm intestinal segments were used for histological and mechanical analysis. The segments were obtained distal (S1), proximal (S2) and further proximal (S3) to the site of obstruction or suturing site. The tri-axial testing included simultaneous torsion, inflation and longitudinal stretching. The lumen size, wall thickness, wall cross-sectional area, and muscle layer thickness increased in S2 and S3 of the obstructed rats (p < 0.001) with the most pronounced changes in S2. The opening angle decreased in S2 in the obstructed group (p < 0.05). The tissue stiffness increased in circumferential and longitudinal direction where as it was softer in shear direction, especially in S2 (p < 0.01). In conclusion, the histomorphological and mechanical properties including shear properties remodeled proximal to the intestinal obstruction site.