Layer-dependent wall properties of abdominal aortic aneurysms: Experimental study and material characterization

Area of Science:

• Biomedical Engineering
• Materials Science
• Cardiovascular Research

Background:

• Abdominal aortic aneurysm (AAA) wall mechanical properties are crucial for rupture risk assessment.
• Layer-specific tissue properties and collagen organization in AAA remain incompletely understood.
• Existing constitutive models may not fully capture the anisotropic behavior of the AAA wall.

Purpose of the Study:

• To establish layer-dependent mechanical properties of the human abdominal aortic aneurysm wall.
• To investigate the spatial organization of the collagen-fiber network within the AAA wall layers.
• To identify and validate a suitable constitutive model for characterizing AAA wall mechanics.

Main Methods:

• Mechanical testing of AAA wall tissue samples from fifteen patients undergoing open surgery.
• Quantitative microscopic evaluation to analyze collagen fiber distribution and orientation.
• Comparison of microstructure-motivated four-fiber family models against Fung- and Gasser-type models.
• Development and validation of a specific diagonal- and circumferential-fiber family model.

Main Results:

• The adventitia exhibited greater stiffness and strength due to higher collagen content and residual tension.
• The intima was under residual compression, while the media showed intermediate properties.
• All layers demonstrated higher circumferential stiffness compared to longitudinal stiffness, attributed to collagen arrangement.
• The four-fiber family model, particularly with fiber angle dispersion, provided superior fitting quality.

Conclusions:

• Histologically-guided material characterization of the layered AAA wall provides critical data.
• The findings can inform the development of reliable criteria for predicting AAA rupture risk.
• Optimized understanding of AAA wall mechanics can enhance endovascular intervention strategies.