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줄기 세포 자극 및 검출을 위한 미세전자기계 소자들

Microelectromechanical Devices for Stem Cell Stimulation and Detection

초록/요약

This dissertation presents microelectromechanical devices for stem cell stimulation and detection. Demonstrations of cell culture and stimulation in the micro devices actuated by electromagnetic forces and pneumatic pressure was performed by the mechanical stimulation (dynamic compression) enhanced the change and differentiation of hMSCs. First, the micro cell exciter actuated by the electromagnetic force is fabricated and tested. It consists of an actuator part and a cartridge-type chamber part. The actuator part has seven magnetic actuators. Each actuator is composed of a permanent magnet, a core and a coil. The chamber part has seven wells, fabricated with poly methylmethacrylate (PMMA) and a cell culture Petri dish. Several kinds of stimulation are tested to identify the effective stimulation in the chondrogenic differentiation of MSCs. Histological assay and reverse transcriptase (RT)-PCR analysis were performed to observe the expression of the chondrogenesis. In this research, Sox9 and type II collagen were observed in the mechanical stimulus group as compared with the control group. The results of this study indicate that the physiologic dynamic stimulation within the appropriate ranges of the voltage and frequency is effective to differentiate MSCs. Second, a pneumatic micro cell chip is designed to culture and apply the mechanical stimulus to stem cells using a pneumatic force with a single pressure. Although the previous results of the experiment using the electromagnetic cell stimulator were very encouraging, there are still several problems with applying stimulus, such as heating, handling and electromagnetic disturbing. A new micro cell chip is able to stimulate stem cells without heating, handling and disturbing. MEMS cell stimulator is based on the pneumatic actuator with a flexible diaphragm. It consists of air chamber and cell-media chamber. The air chamber and cell-media chamber parts have nine wells connected with each other by microchannels. ALP expression shows strongly positive result in the stimulation group. In this system, human bone marrow stem cells may be induced into having differentiation cells by a MEMS cell stimulator. Third, a Pneumatic Micro Cell Chip for applying various degrees of pressures is developed. In previous research, the pneumatic micro cell stimulator with a single pressure is able to perform the stimulating operation for single condition. The bubble trap is sometimes occurred in the micro stimulator problem when the mixed solution is injected into chambers. The new micro cell chip is designed and fabricated to apply various degrees of pressures simultaneously and remove trapped bubbles in chamber. To examine the influence of mechanical stimulation on the differentiation of hMSCs into osteoblast-like cells, the expression of marker proteins and calcium concentration were determined in mechanically stimulated and unstimulated cultures. The changes of the hMSCs under the mechanical stimulation are assessed by monitoring CD90 (Thy-1), actin, alkaline phosphatase (ALP) and alizarin red expression. Osteogenic differentiation also was accelerated by the mechanical stimulation using the new micro cell chip. The results of the study revealed that dynamic compression force from the micro cell chip could enhance the proliferation and osteogenic differentiation of human MSCs in the absence of growth factors. Finally, a built-in capacitive pressure sensor are designed and fabricated. The basic structure of a pressure sensor consists of two electrodes separated by a narrow sensing chamber. The sensing membrane is a 100 ？？m-thick borosilicate glass. The way to detect membrane deformation is by measuring capacitance. The fabricated pressure sensors are integrated into the micro cell chip and tested under various pressures. The built-in capacitive pressure sensor is able to monitor the real time pressures of each cell chambers. The micro cell chip with the capacitive pressure sensor array is tested under various static and dynamic applied pressures. Output voltages are almost linear with respect to the applied pressure. The real-time monitoring of individual pressure increases reliability and throughput in experiment. The new micro cell chip with pressure sensor can provide clearly defined conditions of cell stimulation. This study using the micro cell stimulator could be useful to investigate the role of mechanical signals on the osteogenic turnover of bone marrow-derived MSCs and provide new tools to design novel therapeutic approaches. Bone marrow-derived hMSCs might be induced into chondrogenesis and osteogenesis by the mechanical stimulation.

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목차

1. INTRODUCTION 1
1.1 Motivation 1
1.2 Overview of stem cells 4
1.3 Research objectives 6

2. A MICRO CELL STIMULATOR ACTUATED BY AN ELECTROMAGNETIC FORCE 10
2.1 An electromagnetic type micro cell stimulator 11
2.2 Materials 13
2.3 Methods 13
2.3.1 Cell isolation and expansion 13
2.3.2 Alginate gel formation and in vitro cultivation 14
2.4 Stimulations 17
2.5 Analysis 20
2.5.1 Histology 20
2.5.2 RNA preparation and RT-PCR 20
2.6 Results 22
2.7 Conclusions & discussions 27

3. A PNEUMATIC MICRO CELL STIMULATOR WITH A SINGLE PRESSURE 29
3.1 A Pneumatic micro cell stimulator 30
3.2 Experimental 34
3.2.1 Experimental setup and cell preparation 34
3.2.2 Stimulation 37
3.3 Results and discussion 37
3.4 Conclusions 42

4. A PNEUMATIC MICRO CELL CHIP FOR APPLYING VARIOUS DEGREES OF RESSURES 43
4.1 Micro cell stimulator for applying various degrees of pressures 44
4.2 Fabrication 46
4.3 Methods and materials 50
4.3.1 Cell isolation and culture 50
4.3.2 Experimental setup and operation 51
4.3.3 Cell proliferation 52
4.3.4 Immunofluorescence staining 52
4.3.5 Staining for osteogenesis of MSCs 53
4.4 Results and discussion 54
4.4.1 Cell proliferation 54
4.4.2 Expression of CD90 57
4.4.3 Actin cytoskeleton 59
4.4.4 Osteogenic differentiation 61
4.5 Conclusions 64

5. MICRO CELL CHIP WITH BUILT-IN PRESSURE SENSORS FOR REAL-TIME INDIVIDUAL MONITORING 65
5.1 Micro cell stimulator with built-in pressure sensors 66
5.2 Sensor design 68
5.3 Simulation results 72
5.4 Fabrication 75
5.5 Measurement circuit 78
5.5.1 Carrier wave 78
5.5.2 Charge amplifier 79
5.5.3 Demodulation & amplification 80
5.6 Measurements and results 86
5.7 Conclusions 91

6. CONCLUSIONS AND OUTLOOK 92

REFERENCES 94

PUBLICATION LIST 99

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