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Objectives: Our goal is to develop a double lumen cannula (DLC) for a percutaneous right ventricular assist device (pRVAD) in order to eliminate two open chest surgeries for RVAD installation and removal. The objective of this study was to evaluate the performance, flow pattern, blood hemolysis, and thrombosis potential of the pRVAD DLC. Methods: Computational fluid dynamics (CFD), using the finite volume method, was performed on the pRVAD DLC. For Reynolds numbers <4000, the laminar model was used to describe the blood flow behavior, while shear-stress transport k-ω model was used for Reynolds numbers >4000. Bench testing with a 27 Fr prototype was performed to validate the CFD calculations. Results: There was <1.3% difference between the CFD and experimental pressure drop results. The Lagrangian approach revealed a low index of hemolysis (0.012% in drainage lumen and 0.0073% in infusion lumen) at 5 l/min flow rate. Blood stagnancy and recirculation regions were found in the CFD analysis, indicating a potential risk for thrombosis. Conclusions: The pRVAD DLC can handle up to 5 l/min flow with limited potential hemolysis. Further modification of the pRVAD DLC is needed to address blood stagnancy and recirculation.
The digital image correlation is used to estimate influence of deposited heamocompatible coatings (gold and titanium nitride) on mechanical response of ventricular assist device Religa Heart_Ext made of Bionate II (thermoplastic polycarbonate urethane) under working conditions by comparison of the coated Religa Heart_Ext with uncoated Religa Heart_Ext. The DIC is applied for experimental investigation of the strains and displacements distribution on external surface of the blood chamber of ventricular assist device during loading. The experiment was conducted in a hydraulic system with water at operating temperatures of 25 and 37 °C, as well as under static pressures: 80, 120, 180, 220 and 280 mmHg, and static underpressures: –25, –45, –75 mmHg. The subsequent images were taken after stabilization of pressure on a set level. The applied research method shows that the nano-coating of 30 nm in thickness significantly affects deformation of the blood chamber of Religa Heart_Ext in macro scale. The proposed composition of coatings increases strain on external surface of the ventricular assist device.
The Polish ventricular assist device, POLVAD_EXT, is made of a polymer designed to be covered with a nanocoating of titanium nitride to improve haemocompatibility. A loss of cohesion can occur between the coating and the substrate. An analysis of stress and strain states in a multi-scale model of the blood chamber was performed in the finite element computer program, VADFEM. The multiscale model is composed of a macro model of the blood chamber and a micro model of the titanium nitride (TiN) deposited on the polymer. The finite element method and the goal function, based on the triaxiality factor, are used to solve the problems formulated. The theories of non-linear elasticity and elasto-plasticity are applied. The goal of the paper is to optimise the construction of the POLVAD_EXT with respect to shape parameters.
W artykule rozpatrzono problem numerycznego modelowania stanu naprężeń i odkształceń komory sztucznego serca POLVAD_EXT, pokrytej powłoką TiN w celu zwiększenia biozgodności. Zaproponowano rozwiązanie tego problemu za pomocą metody elementów skończonych (MES). Wykorzystano teorię nieliniowej sprężystości oraz sprężysto-plastyczności. Własności mechaniczne poliuretanu uzyskano za pomocą testów na rozciąganie, natomiast dane dla powłoki TiN otrzymano za pomocą analizy odwrotnej. Zaproponowany model uwzględnia naprężenia własne, powstające w TiN w procesie nanoszenia powłoki. Wykonano eksperyment numeryczny, pozwalający na analizę wpływu grubości powłoki, wartości naprężeń własnych i falistości powierzchni na wartości naprężeń i odkształceń, decydujące o możliwości powstawania mikropęknięć.
The problem of numerical modeling of the stress and strain states in blood chamber of POLVAD_EXT is considered in the paper. The blood chamber is covered by TiN coating to increase its biocompatibility. The finite element method (FEM) is proposed to solve the formulated problem. The theory of nonlinear elasticity and elasto-plasticity is applied. The mechanical properties of polyurethane were obtained in tension tests and for TiN nanocoating by using inverse method. The suggested model takes into account the residual stresses occurring in TiN during deposition process. The numerical experiment was performed for analysis the influence of thickness of coating, residual stress and wave of surface of coating on stress-strain state which decides about capabilities of micro cracks formation.
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