טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentHollander Yaniv
SubjectMorphology Based Constitutive Model for the Coronary Media
DepartmentDepartment of Aerospace Engineering
Supervisors Professor Emeritus David Durban
Professor Emeritus Yoram Lanir
Full Thesis textFull thesis text - English Version


Abstract

Blood vessel biomechanics is an important research topic, incorporating disciplines from continuum mechanics and biology. Understanding vascular mechanics, and its relation to internal structure, is important to the understanding of vascular physiology and the way blood vessels interact mechanically with other organs. A number of vascular pathologies (e.g., atherosclerosis) have pivotal biomechanical background since they are initiated and progress as a result of non-homeostatic mechanical loadings, and the associated biological response of the wall cells. The knowledge of the stress and strain fields in the blood vessel wall will aid in understanding these diseases.

Blood vessels are anisotropic materials manifesting a global orthotropic behavior. They exhibit a nonlinear stress-strain response and are viscoelastic. A typical blood vessel is made of three layers: intima, media, and adventitia. Each layer has a different fibrous structure, and behaves differently in response to applied loads. Importantly, blood vessels are capable of actively changing their diameter and length, by activation of smooth muscle cells in the vessel wall.

Most current vascular constitutive laws are phenomenological, aiming at fitting mathematical expressions with experimental data. The main disadvantage of phenomenological models is that their material constants have no physical interpretation and thus do not offer an understanding on the connection between the tissue architecture and its mechanical characteristics. Fully structural models for soft tissues in general and for blood vessel in particular are important for understanding of tissue mechanical response, and the significance of each of the tissue constituents.

The research thesis presents the development of a fully structural model for the passive coronary media. The model contains a number of independent parameters representing both the three-dimensional (3D) inner fibrous structure of the media and the fibers' properties, and includes the effects of residual stresses and osmotic swelling. Model estimation was based on mechanical data of porcine left anterior descending (LAD) coronary media, which includes measurements of vessel response to radial inflation, axial extension, and twist. Although the full model has twelve parameters, results show that a reduced four parameter model is sufficient to reliably predict the passive mechanical properties. In addition, the model provides good predictions of the LAD media response to data under protocols not used for its estimation.