Purpose The design and optimization of centrifugal blood pumps are crucial for improved extracorporeal membrane oxygenation system performance. Secondary flow passages are common in centrifugal blood pumps, allowing for a high volume of unstable flow. Traditional design theory offers minimal guidance on the design and optimization of centrifugal blood pumps, so it's critical to understand how design parameter variables affect hydraulic performance and hemocompatibility. Methods Computational fluid dynamics (CFD) was employed to investigate the effects of blade number, blade wrap angle, blade thickness, and splitters on pressure head, hemolysis, and platelet activation state. Eulerian and Lagrangian features were used to analyze the flow fields and hemocompatibility metrics such as scalar shear stress, velocity distribution, and their correlation. Results The equalization of frictional and flow losses allow impellers with more blades and smaller wrap angles to have higher pressure heads, whereas the trade‐off between the volume of high scalar shear stress and exposure time allows impellers with fewer blades and larger blade wrap angles to have a lower HI; there are configurations that increase the possibility of platelet activation for both number of blades and wrap angles. The hydraulic performance and hemocompatibility of centrifugal blood pumps are not affected by blade thickness. Compared to the main blades, splitters can improve the blood compatibility of a centrifugal blood pump with a small reduction in pressure head, but there is a trade‐off between the length and location of the splitter that suppresses flow losses while reducing the velocity gradient. According to correlation analysis, pressure head, HI, and the volume of high shear stress were all substantially connected, and exposure time had a significant impact on HI. The platelet activation state was influenced by the average scalar shear stress and the volume of low velocity. Conclusion The findings reveal the impact of design variables on the performance of centrifugal blood pumps with secondary flow passages, as well as the relationship between hemocompatibility, hydraulic performance, and flow characteristics, and are useful for the design and optimization of this type of blood pump, as well as the prediction of clinical complications.

(1) Background: Thrombosis is the main complication in patients supported with ventricular assist devices (VAD). Models that accurately predict the risk of thrombus formation in VADs are still lacking. When VADs are clinically assisted, their complex geometric configuration and high rotating speed inevitably generate complex flow fields and high shear stress. These non-physiological factors can damage blood cells and proteins, release coagulant factors and trigger thrombosis. In this study, a more accurate model for thrombus assessment was constructed by integrating parameters such as shear stress, residence time and coagulant factors, so as to accurately assess the probability of thrombosis in three clinical VADs. (2) Methods: A mathematical model was constructed to assess platelet activation and thrombosis within VADs. By solving the transport equation, the influence of various factors such as shear stress, residence time and coagulation factors on platelet activation was considered. The diffusion equation was applied to determine the role of activated platelets and substance deposition on thrombus formation. The momentum equation was introduced to describe the obstruction to blood flow when thrombus is formed, and finally a more comprehensive and accurate model for thrombus assessment in patients with VAD was obtained. Numerical simulations of three clinically VADs (CH-VAD, HVAD and HMII) were performed using this model. The simulation results were compared with experimental data on platelet activation caused by the three VADs. The simulated thrombogenic potential in different regions of MHII was compared with the frequency of thrombosis occurring in the regions in clinic. The regions of high thrombotic risk for HVAD and HMII observed in experiments were compared with the regions predicted by simulation. (3) Results: It was found that the percentage of activated platelets within the VAD obtained by solving the thrombosis model developed in this study was in high agreement with the experimental data (r² = 0.984), the likelihood of thrombosis in the regions of the simulation showed excellent correlation with the clinical statistics (r² = 0.994), and the regions of high thrombotic risk predicted by the simulation were consistent with the experimental results. Further study revealed that the three clinical VADs (CH-VAD, HVAD and HMII) were prone to thrombus formation in the inner side of the secondary flow passage, the clearance between cone and impeller, and the corner region of the inlet pipe, respectively. The risk of platelet activation and thrombus formation for the three VADs was low to high for CH-VAD, HVAD, and HM II, respectively. (4) Conclusions: In this study, a more comprehensive and accurate thrombosis model was constructed by combining parameters such as shear stress, residence time, and coagulation factors. Simulation results of thrombotic risk received with this model showed excellent correlation with experimental and clinical data. It is important for determining the degree of platelet activation in VAD and identifying regions prone to thrombus formation, as well as guiding the optimal design of VAD and clinical treatment.

No abstract

Disturbed blood flow has been recognized to promote platelet aggregation and thrombosis via increasing accumulation of von Willebrand factor (VWF) at the arterial post-stenotic sites. The mechanism underlying the disturbed-flow regulated endothelial VWF production remains elusive. Here we described a mouse model, in which the left external carotid artery (LECA) is ligated to generate disturbed flow in the common carotid artery. Ligation of LECA increased VWF accumulation in the plasma. Carotid arterial thrombosis was induced by ferric chloride (FeCl 3) application and the time to occlusion in the ligated vessels was reduced in comparison with the unligated vessels. In vitro, endothelial cells were subjected to oscillatory shear (OS, 0.5 ± 4 dynes/cm 2) or pulsatile shear (PS, 12 ± 4 dynes/cm 2). OS promoted VWF secretion as well as the cell conditioned media-induced platelet aggregation by regulating the intracellular localization of vesicle-associated membrane protein 3 (VAMP3) and synaptosomal-associated protein 23 (SNAP23). Disruption of vimentin intermediate filaments abolished the OS-induced translocation of SNAP23 to the cell membrane. Knockdown of VAMP3 and SNAP23 reduced the endothelial secretion of VWF. Systemic inhibition of VAMP3 and SNAP23 by treatment of mice with rapamycin significantly ameliorated the FeCl 3-induced thrombogenesis, whereas intraluminal overexpression of VAMP3 and SNAP23 aggravated it. Our findings demonstrate VAMP3 and SNAP23 as potential targets for preventing the disturbed flow-accelerated thrombus formation.

To investigate the effect of rotor design configuration on hemodynamic features, hemocompatibility and dynamic balance of blood pumps. Computational fluid dynamics was employed to investigate the effects of rotor type (closed impeller, semi‐open impeller), clearance height and back vanes on blood pump performance. In particular, the Eulerian hemolysis model based on a power‐law function and the Lagrangian thrombus model with integrated stress accumulation and residence time were applied to evaluate the hemocompatibility of the blood pump. This study shows that compared to the closed impeller, the semi‐open impeller can improve hemolysis at a slight sacrifice in head pressure, but increase the risk of thrombogenic potential and disrupt rotor dynamic balance. For the semi‐open impeller, the pressure head, hemolysis, and axial thrust of the blood pump decrease with increasing front clearance, and the risk of thrombosis increases first and then decreases with increasing front clearance. Variations in back clearance have little effect on pressure head, but larger on back clearance, worsens hemolysis, thrombogenic potential and rotor dynamic balance. The employment of back vanes has little effect on the pressure head. All back vanes configurations have an increased risk of hemolysis in the blood pump but are beneficial for the improvement of the rotor dynamic balance of the blood pump. Reasonable back vanes configuration (higher height, wider width, longer length and more number) decreases the flow separation, increases the velocity of blood in the back clearance, and reduces the risk of blood pooling and thrombosis. It was also found that hemolysis index (HI) was highly negatively correlated with pressure difference between the top and back clearances (r = −.87), and thrombogenic potential was positively correlated with pressure difference between the top and back clearances (r = .71). This study found that rotor type, clearance height, and back vanes significantly affect the hydraulic performance, hemocompatibility and rotor dynamic balance of centrifugal blood pumps through secondary flow. These parameters should be carefully selected when designing and optimizing centrifugal blood pumps for improving the blood pump clinical outcomes.