Abstract Body (Do not enter title and authors here):
Introduction
Ventricular assist devices (VADs) present great promise as both bridge-to-transplant and destination therapies for patients with end-stage heart failure. However, complications – such as hemolysis, thrombosis, degradation of the von Willebrand factor, and gastrointestinal bleeding – stand in the way of their widespread application. High levels of wall shear stress resulting from poor hemodynamics within the bladed flow domain are primarily responsible. Computational fluid dynamics (CFD) software was used to model the hemodynamic performance of a novel VAD with a looped, toroidal blade design intended to reduce secondary flow effects at the blade tip – and provide detailed insight into the internal flow structures, leading to the shear stress levels within.

Research Questions
Does the elimination of the open blade tip suppress tip recirculation and improve hemodynamics? What are the implications for wall shear stress in such a device, and how can we optimize the geometry as to improve pump performance, while minimizing shear stress?

Methods
The toroidal impeller geometry file was imported into a computer aided design (CAD) software, and the generic scanned design file (STL) was converted to a 3D CAD surface model, from which the flow domain was subsequently extracted. The model was exported to a CFD software, and simulations were subsequently run to assess pump performance and impeller hemodynamics with respect to the wall shear stress parameter.

Results
The VAD achieved an integrated pressure output equivalent to 108.84mmHg at the preliminary target flow rate of 0.5kg/s. The pressure is in the ideal range for supporting left ventricular pumping function. The efficiency of the VAD was calculated to be about 27%, which is reasonable for a VAD micromachine. There were regions of shear stress shown to be above the hemolytic threshold of 400 Pa, however.

Conclusions
This toroidal impeller shows promise, which can be harnessed by applying heuristic, aerodynamic design methods to improve its hemodynamics. That is, further analysis, tuning, and optimization of the blade are necessary to enhance the operating efficiency of the VAD and minimize shear stress levels – specifically, optimization of the blade geometry for more balanced work distribution and reducing profile losses, as well as optimizing the size envelope of the device, currently 25mm in diameter.