Sample preparation based on particle/cell manipulation is an essential process for various biological applications, clinical diagnoses, and therapeutics, since the biological body fluids are usually composed of heterogeneous cellular components. For sample preparation, the target components are required to be isolated from other components that are not of interest or concentrated into well-defined population to improve the accuracy of downstream analyses. Conventionally, density gradient centrifugation and antibody-binding separation technique have been widely used for cell separation. However, those methods have the limitations of the requirement of large bench top centrifuges, physical damage to cells during the centrifugation process, and the requirement of additional labeling processes. In view of this, microfluidics can be a powerful alternative with the advantages of laminar flow with easy flow control, rapid processing time, small sample/reagent volume, and low-priced fabrication process. Therefore, various microfluidic approaches have been developed for cell manipulation, which can be categorized into active and passive methods depending on the use of external force fields. In active techniques, external force fields are applied to manipulate cells based on the differences in inherent properties such as size and density. In passive techniques, cell manipulation can be achieved by using hydrodynamic forces and channel geometries.
Recently, among the microfluidic cell manipulation techniques, there have been increasing interests on the viscoelastic non-Newtonian microfluidics and acousto-microfluidics as the passive and active method, respectively. In the former, easy manipulation of cells without complex channel structures can be achieved, due to the elastic force based on the intrinsic properties of viscoelastic fluids. In the latter, size- or density-based cell manipulation applications have been widely conducted due to its advantages including non-invasiveness, high energy efficiency, fast operation, and easy integration with other microfluidic systems. However, each technique still has the limitations of fixed separable target size of cells depending on the channel dimension and the requirement of sheath flows for pre-alignment of cells.
As such, the main objective of this dissertation is to develop a hybrid microfluidic platform for particle/cell manipulation in various biomedical and clinical applications, by integrating the strengths of viscoelastic and acoustic techniques to overcome the previous limitations of each technique. The device employs viscoelastic migration for sheathless cell pre-alignment in the first stage, followed by size-dependent tunable separation in the second stage.
Prior to the final objective, a single straight channel-based sheathless viscoelastic separation technique was demonstrated and the device performance was characterized with polystyrene particles to validate its working principle. And then, the device was applied to the separation of circulating tumor cells from white blood cells. Subsequently, a novel dome-shaped chamber device-based surface acoustic wave device was developed and the device performance was evaluated by applying the device to acoustic mixing.
Overall, this thesis presents an integrated hybrid microfluidic platform for cell separation. This device can be expected as a powerful tool for versatile cell separation with high efficiency.