Blood-contacting magnetic levitation bearing design using computational fluid dynamics for haemocompatibility.

The Hemocompatibility Assessment Platform (HAP) is a testing rig that will allow for the evaluation of blood trauma caused by individual components of rotary blood pumps including the NeoVAD - a proposed paediatric Left Ventricular Assist Device (LVAD). It is important that the HAP itself is only minimally haemolytic such that the plasma free haemoglobin measured can be assumed to come from the test component. In this study, Computational Fluid Dynamics simulations have been carried out to inform the design of a magnetically levitated motor bearing gap. Simulations show that issues with the original design, namely stagnation regions and large recirculation zones can be mitigated with the introduction of a pipe that introduces blood-flow to the centre of the bearing and disrupts the secondary flow patterns that cause these issues.Clinical relevance- The consequent reduction in shear exposure time will reduce heamolsyis from the HAP. The redesign of the bearing will result in reduced baseline blood trauma from the HAP, thus allowing quantification of test component haemolysis and will therefore aid the design of future paediatric LVADs.

Dynamic Evaluation of an Active Axial Magnetic Levitated Bearing System in a Hemocompatibility Assessment Platform.

To evaluate the hemocompatibility of individual components of our pediatric left ventricular assist device (LVAD), we proposed a hemocompatibility assessment platform (HAP) with a magnetic levitated bearing system. The HAP consists of a drive system utilizing a brushless direct current (BLDC) motor, passive magnetic bearings (PMB), and an active magnetically levitated bearing (AMB) to reduce the hemolysis generated by HAP itself. In this study, we designed and evaluated the performance of the AMB by measuring radial and axial displacements of the rotor resulting from radially destabilizing forces as well as the performance of the drive system when rotated at increasing speeds to 1,200 rotations per minute (rpm). The results show that, with radial disturbance, the AMB is capable of maintaining axial stability for the BLDC motor system. The AMB can control up to 1,200 rpm without any contact between the rotor and stator. Future work includes geometry optimization for the AMB structure and increase the capability to control stable high-speed rotation for the entire system. Clinical Relevance- This work furthers the development of the magnetic levitated bearing system for a hemocompatibility assessment platform that will be used to enhance and accelerate the development of adult and pediatric LVADs.

Hemocompatibility Assessment Platform Drive System Design: Trade-off between Motor Performance and Hemolysis.

Left ventricular assist devices (LVADs) have long been used to treat adults with heart failure, but LVAD options for pediatric patients with heart failure are lacking. Despite the urgent need for long-term, implantable pediatric LVADs, design challenges such as hemolysis, pump thrombosis, and bleeding persist. We have developed a Hemocompatibility Assessment Platform (HAP) to identify blood trauma from individual LVAD components. A HAP would aid in refining pump components before in vivo testing, thereby preventing unnecessary animal sacrifice and reducing development time and cost. So that the HAP does not confound hemolysis data, the HAP drive system consists of an enlarged air-gap motor coupled to a magnetic levitation system. Although it is known that an enlarged air gap motor will have diminished performance, while the larger gap in the motor will cause less blood damage, the trade-offs are not fully characterized. Therefore, in this study we evaluated these trade-offs to determine an optimal rotor diameter for the HAP drive motor. The motor performance was characterized with an experimental method by determining the torque constant for the HAP drive motor with varied rotor diameters. The torque threshold was set as 10 mNm to achieve a nominal current of 3.5A. Hemolysis in the HAP drive motor gap was estimated by calculating scalar shear stress generated in the HAP motor gap analytically and numerically. A design criterion of 30 Pa was selected for scalar shear stress to achieve minimal hemolysis and platelet activation in the HAP drive system.Clinical Relevance- We evaluated a Hemocompatibility Assessment Platform for developing LVAD prototypes that can best balance motor performance and hemocompatibility. This design method can assist with optimizing the drive system during the research stage and illustrates how motor geometry can be tuned to reduce blood trauma.