Experimentelle Untersuchung roter Blutkörperchen mittels digitaler holographischer Mikroskopie
Zusammenfassung der Projektergebnisse
Microcirculation plays an important role in the delivery processes of oxygen to the cells and the transport of by-products from the cells. Red blood cells (RBC) are of special interest in the investigation of blood flow in microcirculation due to the large percentage of these cells on the total blood volume and their relatively large size. The rheological properties of RBCs significantly influence the flow resistance and the oxygen transport within the microcirculatory network and thereby contribute to the circulatory regulation in health and disease. The research proposal aimed at the measurement of the three-dimensional (3D) motion of RBCs in micro channels with a high spatial and temporal resolution via digital holographic microscopy (DHM). Additionally, the applicability of this measurement technique for the detection of the shape of RBCs was investigated. In the course of the project, an experimental setup for DHM measurements was successfully designed and tested for spherical particles and RBC under static and dynamic conditions. The experimental data could be used to evaluate the axial, lateral, and rotational motion of RBCs and a rough view of the cells’ shape could be obtained. Combined measurements of the RBC motion and the surrounding flow field were additionally performed. Since the particle detection methods commonly used at Oshima Lab was limited to very specific configurations, that is, magnification in combination with particle size, it was necessary to develop and program customized routines which are flexibly applicable for the specifications required in the project. The routine was developed and evaluated with respect to the corresponding errors for spherical particles and RBC. Additionally, a double-frame particle tracking velocimetry algorithm was programmed, including a detailed error estimation. To enhance the accuracy of the particle detection, the presently used amplitude information will be coupled with the corresponding phase information to allow a detection of smaller tracing particles for the cell-surrounding flow field. The performed experiments revealed that to gain a thorough understanding of the interaction of the cell’s shape and motion in combination with the surrounding flow field, high-resolution measurements are necessary which require locally precisely defined flow conditions. This discovery led to the design of an inertia-based focusing channel that was successfully manufactured and tested for spherical particles. Bright-field and digital holographic microscopy were used to evaluate the focusing characteristics of various channel designs to investigate the influence of parameters as the channel geometry and the Reynolds number on the focusing. Stable focusing within a wide Reynolds number range was found for several channel geometries with maximum focusing-efficiency values of approximately 97% could be reached. A semi-empirical model was developed to predict the determining forces for the focusing process to enable enhanced design guidelines for configurations which allows focusing of RBC and subsequent high-resolution measurements. The model showed good agreement with experimental results concerning the focusing ability of spherical particles. Even though focusing of RBC was achieved for few configurations, the focusing characteristics did not show similarly good values as for spherical particles and the focusing was quite sensitive to changes in the experimental conditions. Hence, lateral-migration measurements of RBCs were performed which are currently evaluated to supplement the semi-empirical model developed with the respect to the modification of the shape and deformability dependent lift coefficient of the cells. Focusing channels using the enhanced semi-empirical models optimized for focusing of RBCs will be manufactured and tested in the future. Thus, the challenges occurred during the measurement of RBC motion and its shape led eventually to the design of the highly sophisticated measurement environment at Oshima lab comprising of the DHM setup, the novel focusing channels, and the set of tailored adaptive post-processing routines.
Projektbezogene Publikationen (Auswahl)
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“Three-dimensional inertia-based focusing quantification of a stepped microchannel via digital holographic microscopy”, 12th International Symposium on Particle Image Velocimetry, Busan, Korea, 18-22 June, 2017
A. Winzen, M. Oishi, and M. Oshima
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A numerical model-assisted experimental design study of inertia-based particle focusing in stepped microchannels. Microfluid Nanofluid 22, 28 (2018)
A. Winzen, M. Oishi und M. Oshima
