Computational study on the haemodynamic and mechanical performance of electrospun polyurethane dialysis grafts

Abstract

Compliance mismatch between an arteriovenous dialysis graft (AVG) and the connected vein is believed to result in disturbed haemodynamics around the graft-vein anastomosis and increased mechanical loading of the vein. Both phenomena are associated with neointimal hyperplasia development, which is the main reason for AVG patency loss. In this study, we use a patient-specific fluid structure interaction AVG model to assess whether AVG haemodynamics and mechanical loading can be optimised by using novel electrospun polyurethane (ePU) grafts, since their compliance can be better tuned to match that of the native veins, compared to gold standard, expanded polytetrafluoroethylene (ePTFE) grafts. It was observed that the magnitude of flow disturbances in the vein and the size of anastomotic areas exposed to highly oscillatory shear (OSI > 0.25) and very high wall shear stress (> 40 Pa) were largest for the ePTFE graft. Median strain and von Mises stress in the vein were similar for both graft types, whereas highest stress and strain were observed in the anastomosis of the ePU graft. Since haemodynamics were most favourable for the ePU graft simulation, AVG longevity might be improved by the use of ePU grafts.

Computationally guided in-vitro vascular growth model reveals causal link between flow oscillations and disorganized neotissue

“…To accurately estimate these local stresses and strains, we developed an FSI model of this region, which took into account the temporally-varying flow-induced wall deformations as well as the consequent flow profiles. The graft (0.63 mm wall thickness) and the vein (0.385 mm wall thickness) were modeled as a Neo-Hookean material, with a Young's modulus of 1.5 MPa for the graft [16] and 0.455 MPa for the vein [1]. A CFD model of the full geometry with a rigid wall assumption was used to obtain proper boundary conditions for the FSI model and to estimate the wall shear stresses in the graft.…”

“…For the FSI model a similar approach was taken, though for this model zero-pressure vessel diameters needed to be imposed. The zero-pressure venous diameter was set to 7.1 mm, which was approximated using estimates of the average blood pressure at the time of ultrasound diameter measurements [1]. Zero-pressure graft diameter was set to 6 mm.…”

“…The ε strain metric is equivalent to engineering strain and combines both longitudinal and circumferential strain in a single scalar metric. For detailed information regarding the methodology of the simulations, the reader is referred to Quicken et al [17,1]. and used in accordance to the Dutch guidelines for secondary-use materials.…”

“…After 3 days of static culture, the constructs were mounted in the culture chambers of the bioreactor for the application of hemodynamic loading as previously described [21]. To determine the loading conditions that mimic the conditions in vivo, we first examined the expected hemodynamic loads at the vein-graft anastomosis, as computed from the computational fluid dynamic and fluid-structure interaction simulations [17,1]. To each loading condition, n = 5 constructs were assigned to allow for statistical analysis.…”

“…Note that in the in vitro study the shear stress and matrix alignment did not occur at the luminal side but at the outside of the scaffold. Panel b is reproduced with permission [1]. cultured in a bioreactor platform that allows for the independent control of wall shear stress and strain.…”