Passive and active mechanical properties of arteries

Atherosclerosis of the coronary and carotid arteries is the leading cause of mortality and disability in industrialized nations. Both arteries are of great biomedical and clinical interest because they are prone to atherosclerosis and are often treated with balloon angioplasty, stenting or carotid endarterectomy to prevent myocardial infarction and stroke. Our hypothesis is that detailed knowledge of their mechanical behavior can greatly improve the preoperative planning of these therapies, e.g., patient-specific computer simulations can be used to simulate the balloon angioplasty and stenting procedure and optimize the choice of balloon and stent geometry. In addition, mechanical loadings on cells and tissues have been shown to influence the development of atherosclerotic lesions. Three-dimensional models of the artery are therefore required to analyze the distribution of mechanical forces and deformations in the vessel wall. However, most biomechanical studies and material laws consider only the passive and not the active behavior of arteries in their computer simulations. Our approach involves a holistic experimental study of the passive and active behavior of coronary and carotid arteries obtained from pigs. In a future phase, the approach is intended to be extended to human arteries. This will be achieved through passive and active uniaxial (single-axle) and biaxial (dual-axle) extension tests on intact and sectioned specimens, as well as inflation tests on intact arterial segments. The underlying microstructure responsible for the mechanical properties of the tested arterial tissues will be characterized by histological studies of collagen, elastin, and smooth muscle cells. Based on these data, a three-dimensional model capable of describing and predicting the active muscle contraction behavior in addition to the passive behavior of these important arteries will be developed, calibrated, and validated against the extensive data set. An application example, i.e., a computer simulation of the balloon angioplasty and stenting procedure on a coronary artery will be provided. Existing experimental data and an appropriate material law that considers smooth muscle activation in these arteries are very scarce and limited to a single location in these arteries and only to strip tests. In addition, most biomechanical studies and material laws consider only the passive and not the active behavior of the arteries in their computer simulations. The combination of the expertise of both applicants in passive and active experiments and modeling of soft biological tissues at TU Graz and TU Braunschweig is necessary to address all the tasks in the proposed project, and will allow the development of a unique three- dimensional active material law of these two important arteries.