A Multilevel Hierarchical Finite Element Model for Capillary Failure in Soft Tissue

Abstract

Bruising, the result of capillary failure due to trauma, is a common indication of abuse. However, the etiology of capillary failure has yet to be determined as the scale change from tissue to capillary represents several orders of magnitude. As a first step toward determining bruise etiology, we have developed a multilevel hierarchical finite element model (FEM) of a portion of the upper human arm using a commercial finite element tool and a series of three interconnected hierarchical submodels. The third and final submodel contains a portion of the muscle tissue in which a single capillary is embedded. Nonlinear, hyperelastic material properties were applied to skin, adipose, muscle, and capillary wall materials. A pseudostrain energy method was implemented to subtract rigid-body-like motion of the submodel volume experienced in the global model, and was critical for convergence and successful analyses in the submodels. The deformation and hoop stresses in the capillary wall were determined and compared with published capillary failure stress. For the dynamic load applied to the skin of the arm (physiologically simulating a punch), the model predicted that approximately 8% volume fraction of the capillary wall was above the reference capillary failure stress, indicating bruising would likely occur.