Evaluation of mechanical properties of aortic vascular prostheses: comparison among in vitro, theoretical and clinical data

摘要

Vascular prostheses are biomedical devices used for the replacement of segments of arteries, usually of large diameter, which have lost their functionality after stenosis, aneurysms or mechanical traumas [1]. When implanted, a vascular prosthesis undergoes a phenomenon called "dilatation", which consists in an increase of the diameter. This effect of the transmural pressure can be split into a first phase of short term dilatation due to the flattening of the crimps, the elastic deformation of the fibers and the structural rearrangement of the stretched fabric and a second phase of long-term dilatation due to the creep of the fibers, which very often suffer also from the environmental chemical attack. A common measurement of the capability of a vessel to undergo elastic deformations is the compliance, which is defined as the fractional change in volume of the vessel per unit change in the transmural pressure. When a segment of aorta is replaced by a prosthesis exhibiting higher circumferential stiffness, two main consequences arise. The former is the different propagation rate of the pressure waves at the interfaces, which causes wave reflections and eddy currents, that in turn are known to promote the formation of thrombi and hyperplastic neointima. The latter lies in overstresses in the sutures at the anastomoses, due to the different radial dilatation of the prosthesis and the natural vessel: these stresses may cause formation of anastomotic aneurysm, fatigue failure of sutures and tearing of the host artery. The hydraulic matching of two vessels, that permits the perfect transmission of the pressure pulse without reflection, needs matching both the compliance and the cross-sectional area of the vessels.