FIBER ORIENTATION IN PORCINE CORONARIES, AS DESCRIBED BY THE HOLZAPFEL MODEL IS FIXED AT PHYSIOLOGICAL LOADING

摘要

Insight into the mechanical properties of the coronary arterial wall can give valuable information concerning atherosclerosis, wall remodeling, and predicting the effects of medical intervention; e.g. balloon angioplasty [1,2]. Furthermore, knowledge of the mechanical properties of the arterial wall is important in modeling the coronary circulation and explaining its hemodynamical functioning. To determine the material properties of an arterial wall, a mixed experimental-numerical approach can be used in which parameters of a constitutive model are fitted to experimental data. Challenges in applying this approach in-vivo, are that the orientation of the different tissue composites and the unloaded geometry are unknown. Including all these extra parameters, together with the non-linear stress-strain parameters, can easily result in over-parameterization. An example of this is shown by Stalhand et al. [3], where the properties of the aortic wall were successfully determined for in-vivo data using a non-linear parameter estimation scheme. However, to avoid over-parameterization the parameter which accounts for the orientation of collagen fibers had to be prescribed. Since collagen is the main load bearing structure in arteries at physiological loading, it is evident that the orientation of these fibers is very important in modeling the arterial wall. Collagen is continuously formed and degraded. Newly formed collagen is inserted such that it experiences a preferred homeostatic state of stress and strain. This results in a homogeneous circumferential stress distribution and a pressure-invariant reduced axial force [2-5].