Abdominal aortic aneurysm (AAA) represents a degenerative disease process of the abdominal aorta that results in dilation and permanent remodeling of the arterial wall. A fluid structure interaction (FSI) parametric study was conducted to evaluate the progression of aneurysmal disease and its possible implications on risk of rupture. Two parametric studies were conducted using (i) the iliac bifurcation angle and (ii) the AAA neck angulation. Idealized streamlined AAA geometries were employed. The simulations were carried out using both isotropic and anisotropic wall material models. The parameters were based on CT scans measurements obtained from a population of patients. The results indicate that the peak wall stresses increased with increasing iliac and neck inlet angles. Wall shear stress (WSS) and fluid pressure were analyzed and correlated with the wall stresses for both sets of studies. An adaptation response of a temporary reduction of the peak wall stresses seem to correlate to a certain extent with increasing iliac angles. For the neck angulation studies it appears that a breakdown from symmetric vortices at the AAA inlet into a single larger vortex significantly increases the wall stress. Our parametric FSI study demonstrates the adaptation response during aneurysmal disease progression and its possible effects on the AAA risk of rupture. This dependence on geometric parameters of the AAA can be used as an additional diagnostic tool to help clinicians reach informed decisions in establishing whether a risky surgical intervention is warranted.

Typically, tissue-engineered scaffolds mimic the topographical properties of the native extracellular matrix. However, other physical properties, such as the scaffold mechanical stiffness, are not imitated. The purpose of this study was to fabricate scaffolds with improved mechanical properties and investigate their biocompatibility towards endothelial cells and platelets. To enhance mechanical properties, an electrospinning apparatus was developed that fabricates fibers with sheath-core morphologies. Different combinations of cellulose acetate and chitosan were chosen to modulate the mechanical properties of the formed fibers. We hypothesized that mechanically stiffer scaffolds would improve endothelial cell growth and that all scaffolds would be compatible towards endothelial cells and platelets. Endothelial cell-culture conditions were quantified up to 5 days. Migration onto scaffolds was monitored for 10 days. Platelet aggregation, antagonized by thrombin receptor agonist peptide 6, was measured after scaffold incubation. A platelet activation time-course was assessed with the modified prothrombinase assay. As scaffold mechanical stiffness increased, endothelial cell growth within and adhesion to and migration throughout the scaffolds was promoted. Also, scaffolds did not induce platelet aggregation or activation. These results indicate that the mechanical stiffness of engineered scaffolds regulates endothelial cell-culture parameters and that these sheath-core electrospun scaffolds are compatible towards endothelial cells and platelets.

Our goal was to evaluate endothelial cell infiltration into electrospun cellulose acetate scaffolds, with a fiber diameter range of 1–5μm. Chitosan was added prior to electrospinning to increase scaffold stiffness. Fibronectin was added to formed scaffolds to add a specific ligand binding site for cell migration. Human umbilical vein endothelial cells (ECs) were cultured on glass for 1 day. After which, uv light sterilized scaffolds were placed on top of adherent ECs. EC viability, density and morphology on scaffolds and bare glass were investigated for 9 days after scaffold placement. ECs were found within all uv sterilized scaffolds after 1 day in culture. On pure cellulose acetate scaffolds, EC density plateaued on day 4 at a value approximately 50% of the cell density on paired glass. Cell density on scaffolds with chitosan or fibronectin increased continually over the 10 day culture, surpassing EC density on paired glass. Cell viability was high on all scaffolds and glass (>90%). With increased time in culture, the percentage of elongated ECs increased significantly on all scaffolds. ECs can migrate onto electrospun cellulose acetate scaffolds, showing a preference for a three dimensional matrix over two dimensional glass. Addition of chitosan or fibronectin to electrospun cellulose acetate scaffolds enhanced migration against gravity onto scaffolds and EC elongated morphology. Thanks to NIH HL55492.