Numerical analysis of the flow in the model of a venous valve: normal and surgical corrected

The present study aimed to modeling of surgically corrected venous valve. The Arbitrary Lagrangian-Eulerian (ALE) method was used to model the blood–leaflet interactions. The contact process between leaflets was evaluated using a frictionless contact method. The results of the numerical study of the flow in the venous valve after extravasal correction was compared with the results for the normal venous valve.

Investigations on physico-chemical properties of TSPCU nonwoven for application as prosthetic venous valve

Electrospinning is used for producing nonwovens for medical polymer-based implants, such as prosthetic valves or covered scaffolds. In this study, nonwovens for prosthetic venous valves are investigated regarding their morphology and mechanics in physiological medium. Spinning molds were developed based on previous venous valve leaflet designs, 3D printed in different sizes and covered with electrospun nonwovens. Samples were stored in a physiological 0.9% saline at 37°C to investigate the influence of fiber rearrangement and swelling in medium for several weeks. Two different nonwovens of thermoplastic silicone-based polycarbonaturethane (TSPCU) were compared. Tensile test results show that storage in medium has a relevant influence on the mechanical properties. SEM images of TSPCU show substantially increased fiber diameters after 8 days stored in medium. After detaching the valve leaflet nonwovens from the molds, shrinkage of the material of approximately 12% was detected. A suitable valve size could be identified for joining with the stent structure into an interventional prosthetic venous valve. The results demonstrate the influence of storage conditions on the morphological and mechanical properties of electrospun TSPCU nonwovens. For development and dimensioning of venous valve leaflets, this change in mechanical behavior and possible shrinkage of the material has to be considered.

Modelling Particle Agglomeration on through Elastic Valves under Flow

This work proposes a model of particle agglomeration in elastic valves replicating the geometry and the fluid dynamics of a venous valve. The fluid dynamics is simulated with Smooth Particle Hydrodynamics, the elastic leaflets of the valve with the Lattice Spring Model, while agglomeration is modelled with a 4-2 Lennard-Jones potential. All the models are combined together within a single Discrete Multiphysics framework. The results show that particle agglomeration occurs near the leaflets, supporting the hypothesis, proposed in previous experimental work, that clot formation in deep venous thrombosis is driven by the fluid dynamics in the valve.

Surgical repair of a special category of arteriovenous fistula outflow stenosis caused by venous valve hyperplasia

Objective This study evaluated a special category of arteriovenous fistula outflow stenosis caused by venous valve hyperplasia and explored the effectiveness of surgical repair in dealing with this kind of stenosis. Study design This retrospective cohort study was conducted from February 2016 to January 2020 in our center. Patients with arteriovenous fistula dysfunction, including flow rate insufficiency, venous hypertension, thrombosis, and aneurysm dilation enlargement, were selected. Stenosis lesions presenting with venous valve hyperplasia were selected after ultrasound screening. All patients underwent surgical repair and were followed up every 6 months after surgery. Results Forty-three patients (median age, 54.5 ± 11.2 years; 65.1% men) were included. All procedures were technically successful. Based on intraoperative exploration, 56.5% were reconstructed via autologous vein patch, 17.4% of patients were reconstructed with end-to-end reconstruction after cutting the stenotic segment, 13.0% of cases simply had the valve resected, and 13.0% of cases involved a longitudinal incision and transverse suture. All patients returned to routine dialysis the following day and avoided catheter insertion. The mean follow-up time was 22.5 ± 14.0 (range, 1.3–49.8) months. The patency rates at 2 and 4 years were 92.2% and 79.0%, respectively. Valves harvested from patients were analyzed via Masson staining and immunohistochemical staining, indicating collagen fiber and myofibroblast hyperplasia in outflow venous valve hyperplasia (OVVH). Conclusions Outflow venous valve hyperplasia can lead to fistula dysfunction. Ultrasound is the main method to diagnosis OVVH. Special surgical repair can preserve valuable vascular resources and relieve stenosis, is safe and effective, and has a high patency rate.