83 research outputs found
Numerical study of turbulence models in the computation of blood flow in cannulas
In recent years, CFD has become an increasingly used tool in the design of blood-based devices. However, the estimation of red blood cells damage (hemolysis) remains a very important challenge due to the complex rheology of blood and the turbulence present in most pumping devices. The objective of this study was to identify an appropriate turbulence model suitable for predicting hemolysis in Hemodialysis cannula. Several modern turbulence models were evaluated in comparison to Direct Numerical Simulation (DNS), which was used as the gold standard. The fluid dynamics in the cannula was modeled as a coaxial jet in which Reynolds’ number approached 2800. Based on comparison of velocity and stress time-averaged profiles, the Shear Stress Transport (SST) model with Gamma-Theta transition was identified as an optimal compromise between accuracy and computational cost
Magnetically suspended miniature fluid pump and method of designing the same
A rotary pump for pumping fluids through a patient having a housing with an internal region, a stator member and an impeller positioned within the housing and having impeller blades, wherein the impeller is magnetically suspended and rotated, and wherein the geometric configuration of the rotary pump is sized and proportioned to minimize stagnant and traumatic fluid flow within the rotary pump. The plurality of magnetic impeller blades are preferably rare earth, high-energy-density magnets selected from the group consisting of samarium cobalt and neodymium-iron-boron alloy
Automated CFD shape optimization of stator blades for the PediaFlow pediatric ventricular assist device
PediaFlow is a miniature mixed-flow ventricular assist device for neonates
and toddlers. PediaFlow has a fully magnetically levitated rotor which improves
biocompatibility, but the increased length of the rotor creates a long annular
passage where fluid energy is lost. Therefore, a set of helical stator blades
was proposed immediately after the impeller stage to remove the swirling flow
and recover the dynamic head as static pressure. Automated computational fluid
dynamics (CFD) shape optimization of the stator blades was performed to
maximize pressure recovery at the operating point of 1.5 LPM and 16,000 RPM.
Additionally, the effect on hemolysis and thrombogenicity was assessed using
numerical modeling. The optimization algorithm favored fewer blades of greater
length over a larger number of short blades. The ratio of wrap angle to axial
length emerged as a key constraint to ensure the viability of a design. The
best design had 2 blades and generated 73 mmHg of pressure recovery in an
isolated stage. When re-introduced to the CFD simulation of the complete flow
path, the added stator stage increased the pump head by 46% and improved the
pump efficiency from 21.9% to 25.7% at the selected operating point. Automated
CFD shape optimization combined with in silico evaluation of hemocompatibility
can be an effective tool for exploring design choices and informing early
development process
von Willebrand Factor unfolding mediates platelet deposition in a model of high-shear thrombosis
Thrombosis under high-shear conditions is mediated by the mechanosensitive
blood glycoprotein von Willebrand Factor (vWF). vWF unfolds in response to
strong flow gradients and facilitates rapid recruitment of platelets in flowing
blood. While the thrombogenic effect of vWF is well recognized, its
conformational response in complex flows has largely been omitted from
numerical models of thrombosis. We recently presented a continuum model for the
unfolding of vWF, where we represented vWF transport and its flow-induced
conformational change using convection-diffusion-reaction equations. Here, we
incorporate the vWF component into our multi-constituent model of thrombosis,
where the local concentration of stretched vWF amplifies the deposition rate of
free-flowing platelets and reduces the shear cleaning of deposited platelets.
We validate the model using three benchmarks: in vitro model of
atherothrombosis, a stagnation point flow, and the PFA-100, a clinical blood
test commonly used for screening for von Willebrand Disease (vWD). The
simulations reproduced the key aspects of vWF-mediated thrombosis observed in
these experiments, such as the thrombus location, thrombus growth dynamics, and
the effect of blocking platelet-vWF interactions. The PFA-100 simulations
closely matched the reported occlusion times for normal blood and several
hemostatic deficiencies, namely, thrombocytopenia, vWD Type 1, and vWD Type 3.
Overall, the multi-constituent model of thrombosis presented in this work
enables macro-scale 3-D simulations of thrombus formation in complex geometries
over a wide range of shear rates and accounts for qualitative and quantitative
hemostatic deficiencies in patient blood. The results also demonstrate the
utility of the continuum model of vWF unfolding that could be adapted to other
numerical models of thrombosis
In Vitro and In Silico Characterization of the Aggregation of Thrombi on Ventricular Assist Device Cannula
The unacceptably high stroke rate of HeartMate III VAD without signs of
adherent pump thrombosis is hypothesized to be the result of the thrombi
originating on the inflow cannula, ingesting and ejecting emboli from the VAD.
Therefore, inflow cannula thrombosis has been an emerging focus. The inflow
cannula of contemporary VADs, which incorporate both polished and rough regions
serve as useful benchmarks to study the effects of roughness and shear on
thrombogenesis. An in vitro study was conducted to emulate the
micro-hemodynamic condition on a sintered inflow cannula, and to observe the
deposition and detachment patterns. Together with a computational fluid dynamic
tool, this study aimed to provide insight into the optimization of inflow
cannula and potentially reducing adverse neurological events due to upstream
thrombus
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