A multilevel hierarchical finite element model for capillary failure in soft tissue

Area of Science:

• Biomechanics
• Biomedical Engineering
• Tissue Mechanics

Background:

• Bruising, a common sign of trauma and abuse, results from capillary failure.
• The precise mechanism of capillary failure under trauma remains unclear due to scale differences between tissue and capillaries.

Purpose of the Study:

• To develop a computational model for investigating the etiology of capillary failure leading to bruising.
• To analyze stress and deformation within capillaries under dynamic loading conditions simulating trauma.

Main Methods:

• A multilevel hierarchical finite element model (FEM) of the human upper arm was created.
• Nonlinear, hyperelastic material properties were assigned to skin, adipose, muscle, and capillary tissues.
• A pseudostrain energy method was used to manage submodel motion and ensure analysis convergence.

Main Results:

• The model simulated dynamic loading on the arm, mimicking a punch.
• Calculated hoop stresses in the capillary wall were compared against known capillary failure stress.
• Approximately 8% of the capillary wall volume exceeded the failure stress threshold.

Conclusions:

• The finite element model provides a framework for understanding bruise etiology.
• Simulated trauma can induce stresses sufficient to cause capillary failure and subsequent bruising.