The Role of the Mechanical Characteristics and Microstructure of the Porcine Aortic Wall: Implications for Abdominal Aortic Aneurysm Rupture Risk

Abstract

Abstract Introduction Abdominal aortic aneurysm (AAA) represents the increase of the diameter of the aorta by more than 50% in the absence of surgical or endovascular intervention. The risk of rupture and, therefore, mortality is increased significantly in AAA. The role of the mechanical characteristics of the AAA wall is poorly studied. The aim of this study was to determine the mechanical properties of each layer of the porcine abdominal aorta for a better understanding of the role of the microstructural elements of the arterial wall in the development and risk of AAA rupture. Materials and methods In this study, eight tubular segments of the abdominal porcine aorta were examined. From these segments, we processed 13 × 13 mm square samples for biaxial analysis and 15 × 5 mm samples for uniaxial analysis. At the biaxial analysis, the intact wall and each layer (intima, media, and adventitia) were stretched by 25% at a speed of 1% per s and we determined the mechanical characteristics of the samples at the point of failure. Results In the circumferential axis, we found the adventitia (0.233 MPa) to be stronger than the media (0.182 MPa, p = 0.007), intima (0.171 MPa, p = 0.008), and the intact wall (0.192 MPa, p = 0.045). In the longitudinal axis, the adventitia (0.199 MPa) was stronger than the intima (0.117 MPa, p <0.001) and the intact wall (0.156 MPa, p = 0.045), but there was no statistically significant difference compared to the media. Additionally, the adventitia had a greater stiffness than the other two layers (p <0.05 for both layers and axes) and the intact wall (p <0.05 for both axes). Stretching until failure, the adventitia was the strongest compared to the other layers and the intact wall (p <0.001 for all), and it also presented better compliance, with the highest stretch ratio. Conclusions The results indicate that the adventitia layer is the strongest and stiffest compared to the other two layers, being the last mechanical resistance structure of the arterial wall. It is crucial to avoid injuring and aggressively manipulating the adventitia during surgery to maintain the vascular wall's resistance structure. By taking the measures mentioned above, it is possible to prevent postoperative complications like anastomotic pseudoaneurysm and anastomotic rupture.