MICRO OBJECT MANIPULATION BY OSCILLATING BUBBLES

Manipulating of individual microobjects in millimeter- and micro scales has increasingly become an important task in many biomedical applications [1-4] and micro assembling [5, 6]. Most frequent operations include capturing (immobilizing), transporting, rotating, and isolating of individual objects. In this presentation, a new on-chip micro-object manipulation method by oscillating bubbles is presented. When an electrical voltage is applied to a bubble generation electrode on a top glass plate of a chip filled with D.I. water, a bubble is created by electrochemically (electrolysis) and grown on the electrode during the voltage is applied [31]. When the grown bubble contact the bottom plate where a hydrophobic layer is covered, the bubble moves suddenly to the bottom plate due to difference of the surface property between the top and bottom plates, and the voltage is turned off. Note that bubbles prefer to sit on the hydrophobic surface. When a piezo-actuator attached beneath the bottom plate excites the bubble around the bubble resonance frequency, the oscillating bubble generates so-called cavitational microstreaming flow around the bubble [32-35]. The flow can capture the particles near the bubble into the oscillating bubble surface, and the particles can be carried with the oscillating bubble when the bubble is transported by electrowetting on dielectric (EWOD) [35-37]. Note that the capturing force generated by the oscillating bubble is large enough to hold the particles during the lateral bubble movement [35]. The particles can be carried to a target place with the oscillating bubble by EWOD, and then the particles can be leased from the bubble when the excitation is off. The bubble can be also eliminated electrochemically on a platinum catalyst electrode coated with a thin Teflon layer when the bubble is no more necessary. One of the unique features of this platform is that the microbubbles can be on-chip created electrically and transported in any directions by programming and sequentially activating arrays of EWOD electrodes on 2D plane. This manipulation platform allows us to transport and reposition micro-objects.

** Most movie clips are available in the following websites **
http://www.engr.pitt.edu/microfluidics/research.html
http://home.postech.ac.kr/~fluid/research.html


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