Development of an integrated lab-on-a-chip (LOC) platform for multidrug effect analysis

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2019
Atik, Ali Can
This thesis presents analysis, design, fabrication, and testing of microfluidic sub-units designed for a droplet-based multidrug analysis platform. The platform is integrated with normally closed electrostatically actuated microvalves to monitor cytotoxicity of anticancer drugs on single cancer cells encapsulated in microdroplets. Here, elucidation of cancer heterogeneity requires precise functional analysis at single-cell levels which can assist to select effective drug regimens for personalized chemotherapy. One preeminent technique is to utilize droplet microfluidics which enable encapsulation of single cell in its isolated immediate environment in a high-throughput manner and allow to carry out cell-based assays in tiny volumes. The lab-on-a-chip platform is designed to observe the effect of different combinations and dosages of chemotherapeutic agents on K562 leukemia cells and includes mixing, cell focusing, droplet formation and in vitro cytotoxicity screening all in a single chip. Integrated electrostatic microvalves permit the control of drug flow and routing of droplets within microfluidic device. A review of theoretical concepts, corresponding Computational Fluid Dynamics (CFD) simulations and test results are presented separately for microfluidic sub-systems: passive micromixer, droplet formation in a flow-focusing junction, inertial microfluidics for cell focusing. Then, they combined to compose a full droplet screening workflow. Evaluating both experimental results and numerical simulations regarding the contraction-expansion type micromixer structure indicates that it is possible to achieve a mixing efficiency over 80% for sample flows with a wide range of Reynolds numbers. Droplet size distribution controlled by the volumetric flow rates of dispersed and continuous phases is obtained both numerically and experimentally and the studies validate that droplets with an effective size around 50 μm can be generated by adjusting the flow rates of both phases at a high generation rate (>1000 kHz). Moreover, it is shown that the passive micromixer enhances the single-cell encapsulation ratio to a certain degree (up to %42) by hydrodynamically focusing the cells to the middle of the microchannel. The effectivity of doxorubicin on K-562 leukemia cancer cells confined in drug-media drops is measured at single-cell level based on the fluorescence intensity change over 2 hours and compared with a control group which is not exposed to the drug. While modeling the electrostatically actuated microvalve, both analytical models and Finite Element Analysis (FEM) analysis regarding pull-in voltages and displacements are included. Fabricated prototypes are tested to characterize microvalve behavior for pull-in voltage, repeatability, response times and touch area during actuation. Pull-in voltage is measured around 122 ± 10.65 V. The experimental value of pull-in voltage is closely consistent with numerical and analytical studies. Response times for both opening and closing states observed between 1-3 seconds for different valves. Moreover, fabricated moving diaphragms which are sealed with PDMS microchannels are tested under flow to prove that the proposed channel integration allows fluid flow underneath the valve seat when the valve is actuated.