The Spiral Groove Bearing as a Mechanism for Enhancing the Secondary Flow in a Centrifugal Rotary Blood Pump

Abstract

The rapid evolution of rotary blood pump (RBP) technology in the last few decades was shaped by devices with increased durability, frequently employing magnetic or hydrodynamic suspension techniques. However, the potential for low flow in small gaps between the rotor and pump casing is still a problem for hemocompatibility. In this study, a spiral groove hydrodynamic bearing (SGB) is applied with two distinct objectives: first, as a mechanism to enhance the washout in the secondary flow path of a centrifugal RBP, lowering the exposure to high shear stresses and avoiding thrombus formation; and second, as a way to allow smaller gaps without compromising the washout, enhancing the overall pump efficiency. Computational fluid dynamics was applied and verified via bench-top experiments. An optimization of selected geometric parameters (groove angle, width and depth) focusing on the washout in the gap rather than generating suspension force was conducted. An optimized SGB geometry reduced the residence time of the cells in the gap from 31 to 27 ms, an improvement of 14% compared with the baseline geometry of 200 μm without grooves. When optimizing for pump performance, a 15% smaller gap yielded a slightly better rate of fluid exchange compared with the baseline, followed by a 22% reduction in the volumetric loss from the primary pathway. Finally, an improved washout can be achieved in a pulsatile environment due to the SGB ability to pump inwardly, even in the absence of a pressure head.

Differences Between Blood and a Newtonian Fluid on the Performance of a Hydrodynamic Bearing for Rotary Blood Pumps

“…For speeds higher than 1000 rpm and gaps greater than 40 μm, an increase in the bearing gap seemed to further decrease the suspension force ratio, with even lower suspension forces generated when operating with blood. This might be explained by an increased influence of inertia effects compared with the bearing pumping effectiveness, as pointed out elsewhere . With inertia effects dominating, the cross flow tends to become outwardly directed and lower forces are produced.…”

The Impact of Pulsatile Flow on Suspension Force for Hydrodynamically Levitated Blood Pump

“…First, steady-state simulations were performed to acquire the suspension forced by the SGB. In the normal operation of the SGB in the RBP, the bearing gap is commonly between 20 μ m to 300 μ m [7, 11, 20]. Therefore, the bearing gap in the simulation was chosen from 20 μ m to 300 μ m, and the data were calculated every 20 μ m. The boundary condition was set with inlet and outlet pressure of zero.…”

“…Experiments were carried out to validate the suspension performance test method and the effectiveness of the simulation presented above. The schematic of the experimental setup is shown in Figure 5, which is modified from previous devices on suspension force test for hydrodynamically levitated blood pump reported in colleagues' research [11, 22]. A SGB manufactured with ABS was fixed on a motor shaft (EC32 Flat, maxon motor ag, Sachseln, Switzerland) which was controlled by a monitor (maxon motor ag, Sachseln, Switzerland).…”

“…The exposure time of blood flow to high shear stresses of the RBP is demanded to be lower in order to improve its hemocompatibility. Amaral et al [11] introduced an optimized SGB design which can enhance the washout flow between the rotor and pump casing, significantly decreasing the exposure time and improving the overall efficiency of the pump.…”

Bladeless Heart Pump Design: Modeling and Numerical Analysis

“…To this day, multiple clinical data showed major complications with infections, thrombosis, hemolysis, and hemorrhagic events [11][12][13]. Reliability, lifetime, and the type of bearing also have a significant impact on pump hemocompatibility [14,15]. The influence of the pump design on blood can be significant, hence hemocompatibility should be a priority when designing the heart pump.…”