| The roles of blood vessels are to transport oxygen and nutrients to tissues and to remove carbon dioxide and metabolites from tissues. In addition they serve to maintain fluid and solute balance, aid in endocrine function, and provide heat transfer and preserve body temperature. In order to accomplish these functions blood vessel mechanics are varied throughout the vascular tree and are dependent on the physiological requirements at each level of blood distribution (arteries) and collection (veins). In the treatment of disease and injury of vascular tissues, stents have become an increasingly important mechanical tool in maintaining vessel patency. This has been accomplished by deploying these devices directly into blood vessels after balloon angioplasty and for use as scaffolds for vascular grafts used in minimally invasive procedures. Unfortunately, neointimal hyperplasia continues to present a real problem in long-term vessel patency, especially in small caliber vessels. Difficulty in customizing stent-grafts for treatment of a variety of vessel lesion types also continues to be a significant issue. This has been due, in part, to problems like vessel tortuosity, difficulty in achieving access and the lack of perfect apposition of the graft against the vessel wall to eliminate endoleaks. An important issue in solving these problems is in understanding the stress-strain behavior of blood vessels throughout the vascular tree. This study has developed a mechanical model based on the passive mechanics of macromolecular and cellular constituents. The model takes into account volume fractions, molecular and cellular moduli, and the inter-connection (cross-linking factor) of these components. To a first approximation the elastic behavior of vascular tissues in the juvenile porcine model has been solved for low strain moduli, high strain moduli, heel over points and maximum strain. It has also been shown that the remodeling process that leads to neointima formation is due to the stress in the vascular wall applied by the radial forces of vascular Z-stents. |
