Arteries display a nonlinear anisotropic behavior dictated by the elastic properties and structural arrangement of its main constituents, elastin, collagen, and vascular smooth muscle. Elastin provides for structural integrity and for the compliance of the vessel at low pressure, whereas collagen gives the tensile resistance required at high pressures. Based on the model of Zulliger et al. (Zulliger MA, Rachev A, Stergiopulos N. Am J Physiol Heart Circ Physiol 287: H1335-H1343, 2004), which considers the contributions of elastin, collagen, and vascular smooth muscle cells (VSM) in an explicit form, we assessed the effects of enzymatic degradation of elastin on biomechanical properties of rabbit carotids. Pressure-diameter curves were obtained for controls and after elastin degradation, from which elastic and structural properties were derived. Data were fitted into the model of Zulliger et al. to assess elastic constants of elastin and collagen as well as the characteristics of the collagen engagement profile. The arterial segments were also prepared for histology to visualize and quantify elastin and collagen. Elastase treatment leads to a diameter enlargement, suggesting the existence of significant compressive prestresses within the wall. The elastic modulus was more ductile in treated arteries at low circumferential stretches and significantly greater at elevated circumferential stretches. Abrupt collagen fiber recruitment in elastase-treated arteries leads to a much stiffer vessel at high extensions. This change in collagen engagement properties results from structural alterations provoked by the degradation of elastin, suggesting a clear interaction between elastin and collagen, often neglected in previous constituent-based models of the arterial wall.

No abstract

Background and Purpose: Growth and rupture, the two events that dominate the evolution of an intracranial aneurysm, are both dependent on intraaneurysmal flow. Decrease of intraaneurysmal flow is considered an attractive alternative for treating intracranial aneurysms by minimally invasive techniques. Such modification can be achieved by inserting stents or flow diverters alone. In the present paper, the effect of different commercial and innovative flow diverters' porosity was studied in intracranial aneurysm models. Material and Methods: Single and stent-in-stent combination of Neuroform II as well as single and stent-in-stent combination of a new innovative, low-porosity, intracranial stent device (D1, D2, D1 + D2) were inserted in models of intracranial aneurysms under shear-driven flow and inertia-driven flow configurations. Steady and pulsating flow rates were applied using a blood-like fluid. Particle image velocimetry was used to measure velocity vector fields in the aneurysm midplane along the vessel axis. Flow and vorticity patterns, velocity and vorticity magnitudes were quantified and their value compared with the same flows in absence of the flow diverter. Results: In absence of flow diverters, a solid-like rotation could be observed in both shear-driven and inertia-driven models under steady and pulsatile flow conditions. The flow effects due to the insertion of low-porous devices such as D1 or D2 provoked a complete alteration of the flow patterns and massive reduction of velocity or vorticity magnitudes, whereas the introduction of clinically adopted high-porous devices provoked less effect in the aneurysm cavity. As expected, results showed that the lower the porosity the larger the reduction in velocity and vorticity within the aneurysm cavity. The lowest-porosity device combination (D1 and D2) reached an averaged reduction of flow parameters of 80% and 88% under steady and pulsatile flow conditions, respectively. The reduction in mean velocity and vorticity was much more significant in the shear-driven flows as compared to the inertia-driven flows.