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Date of Award

2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

College, School or Department Name

Department of Mechanical Engineering-Engineering Mechanics

First Advisor

Choi, Chang Kyoung

Abstract

The thesis is separated into two topics: (I). Microfluidic diode pumping and (II). Rapid detection of stem cell differentiation using ITO Opto-electric Sensing.



Part-I: Microfluidic diode pumping Electroosmotic micropump (EOP) is a common microfluidic tool. However, the characteristics of the EOPs have not been fully discovered. The research discovers the biological applications and design insights of the EOPs.

(1). Dynamic microfluidic cell culture platform: The research explores an electroosmotic diode pump for a biological application of the dynamic cell culture platform. The ultra-low EOF is applied by a surface mount diode in this research. The flow rates are controlled between 2.0 ~ 12.3 nL/s in a high salt concentration (>10 mM) aqueous solution. The A549 human lung cancer cells are cultured for a biocompatibility experiment under the ultra-low volumetric flow rate environment.

(2). Effect of diode connection and electrode location on diode pumping volume flow rates: The research describes a method to increase volume flow rates and prevent the chemical electrolysis in the diode pump. The diodes, which are connected in parallel and series, are examined. A capacity of surface charges can be increased by connecting diodes. The volume flow rates of EOF are controlled by the capacity. The volume flow rate increases from 2.22 ~7.6 nL/min at 10 Vpp with increasing diodes from 1 ~ 3 when the diodes are connected in parallel. While the diodes are connected in series from 1 ~ 3, the volume flow rate increases 2.22 ~ 3.34 nL/min. A direction reverse EOF is found. The reverse EOF is generated on PDMS surface, which seems resistant to the diode EOF. According to our mathematical model, it is not very efficient to increase the volume flow by connecting the diodes in series. However, the volume flow rates still can be efficiently controlled if the connection methods can be designed precisely.

(3). Hybrid electroosmotic microfluidic pumping system: A hybrid AC-DC electroosmotic pump is developed to solve a problem (on a flow direction) of the AC electroosmotic pump (EOP). ACEOP provides high flow rates and longer operating time solutions for the microchannel. However, the disadvantage of ACEOP is flow direction change. The ACDC EOP is a hybrid of alternating current (AC) and diode EOPs. The electrode patterns for the AC-DC EOP are symmetrically designed to avoid unwanted ACEOF generation. The flow rate of the AC is from 14 μm/min ~ 144 μm/min for the input range of 0 ~ 10 Vpp and the Diode EOP is from 0 μm/min ~ 95 μm/min. The response time to change flow directions is almost instantaneous. This hybrid system seems very useful for a microfluidic environment requiring both constant flow in one direction and rapid flow direction change in short periods of time such as sample resuspension.



Part-II: Rapid detection of stem cell differentiation using Indium Tin Oxide opto-electric sensing

The development is to evaluate and detect the mesenchymal stem cells (MSCs) while MSCs are differentiating into the osteoblast lineage and retains the conventional detection methods. Both of H9MSCs and hMSCs have similar differentiation response while treating with the same induction media. The developed ITO-OECSS allows us to simultaneously record the differences of the impedance and images during the differentiation. During the differentiation, the resistance of the H9MSCs increases 7 ~ 32 % in 0.2 hours and hMSCs increases 0 ~ 17 % in 1 hour. In order to compare the impedance between H9MSCs and hMSCs, the reference impedance is selected on confluence cultured hMSCs before induction. The results show that the H9MSCs obtain faster and stronger attachment and better calcium secretion than hMSCs. The results indicate that the stemness of the H9MSCs is better than hMSCs. The developed ITO-OECSS can be used to detect the stem cell differentiation in an early stage and classify the stemness between similar stem cells.

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