Optimal bearing gap of a multiarc radial bearing in a hydrodynamically levitated centrifugal blood pump for the reduction of hemolysis

We have developed a hydrodynamically levitated centrifugal pump as a bridge-to-decision device. The purpose of the present study is to determine the optimal bearing gap of a multiarc radial bearing in the developed blood pump for the reduction of hemolysis. We prepared eight pump models having bearing gaps of 20, 30, 40, 80, 90, 100, 180, and 250μm. The driving conditions were set to a pressure head of 200mmHg and a flow rate of 4L/min. First, the orbital radius of the impeller was measured for the evaluation of the impeller stability. Second, the hemolytic property was evaluated in an in vitro hemolysis test. As a result, the orbital radius was not greater than 15μm when the bearing gap was between 20 and 100μm. The relative normalized index of hemolysis (NIH) ratios in comparison with BPX-80 were 37.67 (gap: 20μm), 0.95 (gap: 30μm), 0.96 (gap: 40μm), 0.82 (gap: 80μm), 0.77 (gap: 90μm), 0.92 (gap: 100μm), 2.76 (gap: 180μm), and 2.78 (gap: 250μm). The hemolysis tended to increase at bearing gaps of greater than 100μm due to impeller instability. When the bearing gap decreased from 30 to 20μm, the relative NIH ratios increased significantly from 0.95 to 37.67 times (P<0.01) due to high shear stress. We confirmed that the optimal bearing gap was determined between 30 and 100μm in the developed blood pump for the reduction of hemolysis.