Collagen remodeling in side-to-side bowel anastomoses

Side-to-side anastomosis is a surgically constructed connection often performed after a diseased portion of bowel is removed. This operation causes a highly non-linear and non-native bowel geometry. Though the correlation between this geometry, internal pressure, and bowel tissue's mechanics is critical to prevent leakage, it is currently poorly understood. Here, we integrate finite element modeling (FEM) and experiments to study the remodeling process of collagens in the strength bearing layer, the submucosa, of bowels with side-to-side construction. The bowel is modeled as a composite structure of two muscular layers, and a cross-ply submucosa layer with two symmetric, aligned collagen families. A remodeling process developed due to the stress states in the bowel tissue is used to study changes in collagen's distribution. Simulations show that under internal pressure, the anastomosis opens and leads to remote stress-focusing locations. The stress state here resembles a biaxial state that causes collagens to remodel towards a more random distribution. This is consistent with experimental measurements of collagen fiber dispersions from anastomotic geometries which indicate that active remodeling process might occur to alleviate high stress induced by surgical operations.