Evaluating Plasma Skimming with Different Groove Shapes of Hydrodynamic Bearings for Applying to Blood Pumps by Cells Visualization

Abstract

As a potential solution for solving the hemolysis problem inside the narrow bearing clearance of hydrodynamically levitated blood pumps, plasma skimming has been observed and verified with spiral groove bearings. The objective of this study is to investigate and improve the plasma skimming effect by including the consideration of the red blood cells (RBCs) flow for the hydrodynamic bearing groove shape design. We designed a test rig to imitate the shear flow conditions inside the hydrodynamic bearing clearance. By visualizing RBCs inside the bearing clearance, plasma skimming efficiency with three different designs of groove shapes, referring to PlateA, PlateB, and PlateC, were evaluated and compared under a clearance size of 25 μm, a rotational speed of 2400 rpm, and a flow rate of 150 ml/min conditions. The flow of RBCs inside the clearance was photographed by a high-speed camera with a magnification lens. The plasma skimming efficiency was evaluated by comparing the measured hematocrit using the camera and the measured hematocrit of blood in the circuit. The in vitro blood tests were repeated three times for each designed groove shape with 1%-5% hematocrit human blood as the working fluid. The Student's t-test result of plasma skimming efficiency among three designed shapes showed that there was a significant difference between PlateA and PlateC at hematocrit of 5%, 4%, 3% and 2%, respectively. It is testified that the groove shapes of hydrodynamic bearings have a significant influence on the plasma skimming effect occurring in the bearing clearance.