Session: 06-09-04: Computational Modeling in Biomedical Applications - IV

Paper Number: 112330

112330 - Computational Modeling of an Aortic Medial Ring: Effect of Residual Stresses on a Mechanical Behavior of the Aortic Ring 

The aorta is the largest artery in an animal body, which is not only a conduit tube of blood but also an organ central to regulating the pulsatile flow originating from the left ventricle. The mechanical and structural characteristics of an aortic media mainly composed of smooth muscle cells have profound effects on the physiology and pathophysiology of the aorta. However, many aspects of the aortic tissue are yet fully understood, partly due to the inherent layered wall structure and regionally varying residual stresses.

In the present study, it was hypothesized that a hypertensive aorta would be closely associated with an extraordinary or unusual stress/strain distribution at anatomically specific sites in the aortic media, which predominantly controls aortic wall mechanics. Namely, some mechanical symptoms or precursors of such inhomogeneities related to hypertension can be readily and noninvasively detected even at a very early stage when an in vivo-like computational aorta model is available.

Our recent works have demonstrated that a mechanical interaction between the smooth muscle layer (SML) and elastic lamina (EL) in the aortic media can be computationally reproduced using a simplified finite element (FE) “unit” model. Nevertheless, it is questionable whether this simplified FE model we created can be representative of the structure of a real medial wall and its modeling technique would be applicable to develop a more sophisticated and structure-based aortic FE model.

Thus, this study aimed to computationally represent EL buckling in the aortic medial ring at unloaded state, and to reproduce transmural variation in EL waviness across the vascular wall. We employed Design of Experiments and optimization technique, while applying them to a series of simulations using the unit model to obtain an idealized stress distribution through the wall thickness. By doing so, we successfully identified a preferable boundary condition given to an initial reference configuration of the aortic “ring” model. We also confirmed that the inner and outer layers of the medial wall were subjected to compressive and tensile residual stresses, respectively, at the unloaded state (closed ring), implying that the ring model will open spontaneously when it is radially cut.

Consequently, the residual stresses computed at such a stress-free condition (open ring) were found to be comparable well with the analytically predicted values, ~10 kPa for SML and −35 kPa for EL, partially supporting the validity of our modeling approach. Although further study is still required, the information obtained here will greatly help improve the understanding of basic aortic physiology and pathophysiology, while simultaneously providing a basis for more sophisticated computational modeling of the aortic wall.

Presenting Author: Atsutaka Tamura Tottori University

Presenting Author Biography: Dr. Atsutaka Tamura is a Professor in the Department of Mechanical and Aerospace Engineering at Tottori University. He received his Master’s Degree in Aerospace Engineering from Nagoya University in 1998 and his Ph.D. degree in Mechanical Engineering from Nagoya Institute of Technology in 2008. Prior to his current appointment, he worked as a research scientist for Toyota Central R&D Labs., Inc. for 15 years. His research interests lie in the field of biomechanics, e.g., human body modeling, numerical analysis for injury prediction, and mechanical characterization of biological materials.

Authors:

Atsutaka Tamura Tottori University
Koki Matsumoto Tottori University, Graduate School of Sustainability Science
Jun-Ichi Hongu Tottori University