微流體系統因其具有製程簡易、裝置成本低、所需樣品量少、電場控制精準、與細胞尺度相近等優點，為一適合進行細胞實驗之生物性檢測平台。本研究利用微流體裝置探討排列纖維母細胞(NIH-3T3)的方法，以及利用排列過後的細胞進行趨電性研究的可能性。因傳統趨電性實驗需針對單細胞做追蹤，相當耗費人力及時間，在進行趨電性實驗前將細胞排列為特定圖形，可免去單細胞追蹤的必要性。本研究嘗試兩種方式排列細胞：(1)以雙層微流道裝置組成的物理性可逆氣閥及；(2)交流介電泳力。前者可避免不均勻的表面性質於施加趨電性電場時引發擾流或是不均勻電場而影響細胞遷移，但在操作中容易因流體壓力過大而使得閥無法緊閉，因而無法將細胞排列在特定區域。而交流介電泳力於適當導電度、頻率和電場等操作條件下於細胞圖形化有相當顯著的成果，本研究測試不同電場值(100 V/cm ~ 400 V/cm)以及不同頻率下(100 kHz ~ 40 MHz)的細胞排列情形，找出最適合在本研究下排列細胞的電場與頻率為40 MHz、160 V/cm，細胞於此條件下可排列為40個細胞的小群體，且有高存活率。除此之外，傳統之趨電性實驗所使用之金屬電極若長時間直接接觸到細胞本體，容易造成細胞毒害的情形，亦對實驗造成某些程度上之限制，因此本研究利用洋菜膠及導電高分子聚二甲基二烯丙基氯化銨兩種材料分別製備鹽橋以阻隔金屬電極與細胞本體之接觸，確保細胞於實驗進行間之活性與狀態。在施加1 V/cm、2 V/cm直流電場下，利用2 %洋菜膠鹽橋作為傳導媒介之微流體裝置中纖維母細胞NIH-3T3表現出趨向負極的趨電性行為。NIH-3T3細胞的行為與文獻中報導結果吻合，並證實交流介電泳可用於排列細胞且不改變細胞活性。導電高分子鹽橋比起洋菜膠更易於微流道中製作，因此本研究選用此材料進一步縮小裝置整體體積，在高分子單體(Diallyldimethyl- ammonium chloride)、光起始劑(2-hydroxy-4'-(-hydroxyethoxy)-2-methyl- propiophenone)、交聯劑(N,N'-methylenebisacrylamide)的劑量比例為2 ml：1.4 g：1.4 g時，照射UV光20秒後可聚合固化鹽橋，但製備出的鹽橋在趨電性實驗中隨著時間而體積增加，因此無法提供穩定的電場。

Microfluidc system is a good platform for biological studies. It has advantages of easy fabrication, small amout of sample required, precise control of electric field , and comparable dimension to biological micro-environment. This study focuses on the patterning of cells in the microfluidic device and its application on investigating the electrotaxis behavior of the fibroblast NIH-3T3 cells. Conventional electrotaxis experiment requires single-cell tracking along the experiment and it is a labor and time consuming process. Patterning cells into specific area or shape can simplify the observation of electrotaxis because the change of pattern can indicate the tendency of cell movement. A bilayer microfluidic device was first applied to pattern cells into particular regions by controlling a pneumatic valve. Without changing the chemistry or the topography of the surface, chaotic or enhanced hydrodynamic flow or electric field will not be introduced during electrotaxis experiment. However, the micro-valve was not robust enough to resist the hydrodynamic pressure introduced by cell flow. Therefore, we turned to alternating current dielectrophresis(ACDEP) to pattern cells to specific region and found that at 40 MHz,160 V/cm was optimal for cell patterning for high viability and suitable size of cell group. To avoid direct contact betwee metalic electrodes and cells, we applied two biocompatible materials：agar and diallyldimethylammonium chloride to fabricate the salt bridge and prevent the toxicity produced in electrolysis of medium. In electrotaxis experiments using agar salt bridge, the fibroblast NIH-3T3 cells moved to the cathode under 1 V/cm, 2 V/cm. These results agree with those in previous reports and validate that ACDEP was a suitable method for cell patterning. To make the size of the devices much smaller, salt bridge composed of 97.2 wt% diallyldimethylammonium chloride,1.4 wt% 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone,and 1.4 wt% N,N'-methylenebisacrylamide was fabricated on-chip by exposing the mixture in microchannel under UV light for 20s. However, the salt bridge expanded during the electrotaxis experiment and failed to provide stable electric field to the cells.

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