Acoustofluidic preparation of whole blood components

Abstract: Whole blood is rich in information about the physical state of an individual and is routinely used in a variety of clinical and research applications. In this thesis, the use of a microfluidic technique called acoustophoresis for separation of different blood components is explored. Acoustophoresis uses an ultrasonic standing wave field to manipulate cells in a microfluidic device. Cells within the standing wave field will experience forces which move the cells either to the place of minimum pressure, the node, or to the place of maximum pressure, the anti-node. The strength of the acoustic force is dependent on the cells’ properties such as size, density, and compressibility in relation to its surrounding medium. In the first two papers a method is described to use affinity-bead-mediated acoustophoresis toseparate cells which otherwise cannot be acoustically discriminated. Cells of interest were labeled with spherical particles creating large and dense bead-cell complexes which moved faster in the acoustic field compared to unbound cells. The performance was comparable to standard magnetic separation and no effect of the acoustic separation method on viability, cell proliferation or clonogenic stem cell capacity was observed. The third paper investigates the possibility to separate blood cells with similar acoustic mobilities. By changing the properties of the surrounding medium mononuclear cells reduced their mobility in relation to red blood cells and could be successfully separated. The outcomes in terms of efficiency and purity were comparable to conventional separation methods. Next, the possibility to enrich tumor cells from patients undergoing stem cell transplantation was explored. Tumor cells spiked into apheresis products were acoustically separated based on their size differences without interfering with the cells’ viability, T cell activation, and tumor cell proliferation capacity. For the separation outcome a stable temperature is crucial. In the fifth paper a new chip holder was designed to employ an air-cooling unit in order to remove excessiveheat and allow better heat distribution during the separation process. The system allowed high-throughput multiplex separation of particles at flow rates up to 500 μL/min and concurrent separation of the different white blood cell subgroups, i.e. lymphocytes, monocytes, and granulocytes, was achieved for flow rates up to 300 μL/min. Last, to predict the possibility to separate cells in an acoustic standing wave field it is crucial to know the cells properties. Therefore, a method to statistically estimate the cells biomechanical properties based on acoustophoretic separation data was developed. The work presented here shows the diversity, capability and usability of acoustophoresis for whole blood fractionation.