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In this study,patterning of fibroblasts,NIH-3T3 cells,by alternating current dielectrophoresis (ACDEP) is performed to make the electrotaxis observation much easier and more effective.The movement of the cells under the effect of an electric field is called electrotaxis.Traditional methods of cell patterning change either the chemistry or the topography of a surface.Unfortunately,when an external voltage is applied,these alternations may cause chaotic electric field or enhanced hydrodynamic flow.The non-uniform electric field and hydrodynamic flow will affect the movement of cells.A physical and reversible method was required to pattern cells without influencing the surface properties.Patterning cells by ACDEP is one promising method that fits above criteria.It can arrange cells between electrodes with a specific pattern and thus electrodes do not interfere with cell movement.Several types of the electrodes were designed and fabricated (Fig.1) for pulling the cells to higher electric field (positive dielectrophoresis).The best alternating frequency for accurately patterning cells to specific regions is 36MHz and electric field should not exceed 400 V/cm to preserve cell viability.Cell populations can be arranged with specific patterns when different electrodes were applied (Fig.2).This method provides a straightforward and rapid way to observe electrotaxis because single cell tracking is not needed.The change in the cell distribution can represent the directedness of cell movement.We are currently investigating the effects of different conductivities of the media that can achieve effective and noninvasive cell patterning.