Anisotropic AAA: computational comparison between four and two fiber family material models

Area of Science:

• Biomedical Engineering
• Computational Mechanics
• Cardiovascular Research

Background:

• Abdominal aortic aneurysm (AAA) is a prevalent cardiovascular disease in the elderly.
• Accurate biomechanical modeling of AAA wall is crucial for understanding pathogenesis and clinical management.
• Existing constitutive models for AAA tissue show varying degrees of accuracy.

Purpose of the Study:

• To compare the predictive capabilities of two-fiber (2FF) and four-fiber (4FF) constitutive models for AAA wall behavior.
• To investigate the influence of different strain energy functions (SEFs) on AAA inflation simulations.
• To assess the impact of data extrapolation on model predictions.

Main Methods:

• Implemented 2FF and 4FF constitutive models in a finite element code.
• Simulated AAA inflation under physiological axial stretch (20%).
• Compared model predictions for stress distribution under simulated AAA conditions.

Main Results:

• Both 2FF and 4FF models fit experimental biaxial test data well.
• Significant differences in predicted stress outcomes between the 2FF and 4FF models were observed during AAA inflation.
• The 4FF model predicted increased circumferential stress, while the 2FF model predicted higher axial stress.

Conclusions:

• The choice of constitutive model significantly impacts biomechanical predictions for AAA.
• Model discrepancies arise from SEF behavior outside the range of fitting data, particularly during extrapolation.
• Experimental data should ideally be acquired under conditions relevant to the intended application, such as AAA inflation.