Cracking of soft collagenous tissues under suture retention

Soft collagenous tissues consist of collagen fibers and soft matrix, such as skin, muscle, and heart valve, etc. Suture of the tissues is ubiquitous in surgery, which may cause fracture of tissues due to inevitably introduced defects. However, the cracking mechanism of soft collagenous tissues under suture retention remains elusive. Herein, we use bovine pericardium as a model tissue to study the suture related fracture considering various fiber orientations. Fracture tests reveal distinct toughness and fracture modes of the tissue depending on the fiber orientation, such as crack propagation and crack deflection. The maximum J-integral criterion has been established to predict the direction of crack propagation in the tissue. We further conduct suture retention test to evaluate the suture resistance of tissues, and find two different failure modes: fracture and cutting. Microscopic examination of the fracture surface demonstrates that the tissue can rupture with long fiber pullout, cut through matrix failure, or cut by a combination of fiber break and pullout. The cohesive element model is used to analyze the cutting mode. The predicted failure modes and force-displacement curves match well with experiments. This paper may provide guidance to surgical operations and benefit new artificial collagenous materials.