A simple method for the investigation of cell separation effects of blood with physiological hematocrit values.

Even though the separation of blood into erythrocyte-rich and erythrocyte-poor areas is well known in physiological setups such as small vessels, it has recently come into focus in small gaps in cardiovascular applications. Studies show that separation effects occur, for example, in gaps in hydrodynamic bearings, where they can have a positive effect on hemolysis. Separation effects depend on the hematocrit value, but due to visualization issues, studies in small gaps used very low hematocrit values. In this study, a test setup and an evaluation method for the investigation of separation effects of blood with hematocrit values of 30, 45, and 60% were developed. The erythrocyte distribution was evaluated by means of gray scale value distribution. This principle is based on the fact that an erythrocyte-rich region is more opaque than an erythrocyte-poor region. The experimental setup is designed in a way that no further processes (e.g., fluorescence labeling) need to be carried out which might change the properties of the membrane of the erythrocytes, and therefore their flow properties. Additionally, the method is executable with basic laboratory equipment, which makes it applicable for many laboratories. To validate the feasibility of the method, the influence of the diameter and the flow rate on the migration of erythrocytes were studied in micro channels for three different physiological hematocrit values. Even though no individual cells were traced, plasma layer and areas of high erythrocyte concentration could be identified. Dependencies of the erythrocyte distribution on flow rate and channel diameter were validated. The influence of the hematocrit value was demonstrated as well and showed the hematocrit value to be a crucial factor when investigating cell separation. The experimental results were consistent with findings in the literature. As the developed method is suitable for physiological hematocrit values and easy to handle, it provides an optimal basis for cell separation studies in gap models with whole blood, for example, hydrodynamic bearings, where it can be used to optimize these devices.