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Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow patterna)
a)Paper submitted as part of the 3rd European Conference on Microfluidics (Guest Editors: J. Brandner, S. Colin, G. L. Morini). The Conference was held in Heidelberg, Germany, December 3–5, 2012.
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10.1063/1.4817006
/content/aip/journal/bmf/7/4/10.1063/1.4817006
http://aip.metastore.ingenta.com/content/aip/journal/bmf/7/4/10.1063/1.4817006

Figures

Image of FIG. 1.
FIG. 1.

Design of the electrode pair under consideration.

Image of FIG. 2.
FIG. 2.

Experimental setup and array of EWOD chips in the upper frame.

Image of FIG. 3.
FIG. 3.

Axisymmetric flow within a sessile PBS drop in air, under oscillating EWOD as observed from (a) above with fluorescent tracers, (b) along a drop cross-section (use of a 100 m thick laser sheet, the white dotted contour indicates the averaged half-spherical drop shape), and (c) experimental velocity field as obtained from micro-PIV along a meridian cross-section; arrows emphasize the presence of the toroidal counterrotating vortex pair. For the sake of comparison, (d) toroidal vortices as calculated along a meridian cross-section. Chip with two half-circular electrodes separated by a gap of 3 m, actuation frequency: f = 110 Hz, RMS voltage: 60 V, wave number: k = 2.

Image of FIG. 4.
FIG. 4.

Comparison (modes k = 2, 4, 6) for a sessile PBS drop in air between the velocities as measured at the apex of the drop or numerically predicted from Eq. (1) with θ = 0. The experimental velocity is obtained from micro-PIV measurements especially performed on the small area bounded by the red rectangle displayed in the snapshots (tracers: fluorescent beads). The streamlines as computed numerically are made visible on the RHS of the snapshots. Chip with two half-circular electrodes separated by a gap of 3 m, RMS voltages: 60 V (k = 2), 75 V (k = 4) or 91.7 V (k = 6). Consider also Ref. for imaging of the streamlines.

Image of FIG. 5.
FIG. 5.

Frequency-dependence of the location of U373B cell agglomerates (as imaged from the side under continuous lighting along the direction of free motion, as indicated from the horizontal dotted line) and drop shape oscillations induced by capillary waves as observed under stroboscopic lighting. For the frequencies f = (300 Hz, 600 Hz, 1 KHz), the displayed amplitude of the capillary waves is the real one multiplied by a factor 5 (better readability). Chip with two half-circular electrodes separated by a gap of 100 m. Scaling in mm is displayed on the horizontal axis of each snapshot. RMS voltage applied: 91.7 V. Oil is used as ambient phase.

Image of FIG. 6.
FIG. 6.

Positioning of agglomerates as a function of the EWOD actuation frequency, as described by the angular deviation, θ (colatitude).

Image of FIG. 7.
FIG. 7.

Frequency-dependence of the vertical positioning of U373B cell clusters as made evident from side and top views of a drop consisting of culture medium in oil as ambient phase. Pinch-off is made evident at the location where the contact line crosses the axis of the electrode gap (top view). Chip with two half-circular electrodes separated by a gap of 100 m. Mean wetting radii: see also Fig. 9 , RMS voltage: 91.7 V.

Image of FIG. 8.
FIG. 8.

Impact of drop vortical flows on different types of biological cells: (a) red blood cells, (b) white blood cells, (c) U373B cells, as demonstrated from side view along the direction of free motion (Fig. 3 ). Oil is used as ambient phase. Chip with two half-circular electrodes separated by a gap of 100 m, RMS voltage: 91.7 V.

Image of FIG. 9.
FIG. 9.

Dynamics of anisotropic EWOD as characterized by oscillating wetting diameters (◆) and contact angles (▲) either along the direction of free motion (left part) or along the electrode gap (right part). The symbol, , is the argument of the oscillating drop shape. The arrows connect the curves to their respective y-axis. Experimental conditions: oil is used as ambient phase; half-circular electrodes separated by a gap of 100 m; applied RMS voltage: 91.1 V; actuation frequencies: (a) f = 150 Hz or (b) f = 1 KHz.

Tables

Generic image for table
Table I.

Wetting data in static conditions with the EWOD chip considered in this study.

Generic image for table
Table II.

Characteristics of the biological cells.

Generic image for table
Table III.

Typical values of the parameters associated to streaming theory for water drops in air (drop volume: 1.5 l).

Generic image for table
Table IV.

Eigenmodes and resonant frequencies for PBS drops in air (drop volume: 1.5 l). Consider also Ref. for viewing resonant drop shape oscillations.

Generic image for table
Table V.

Eigenmodes and resonant frequencies for PBS drops in oil (drop volume: 1.5 l).

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/content/aip/journal/bmf/7/4/10.1063/1.4817006
2013-07-25
2014-04-17
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow patterna)
http://aip.metastore.ingenta.com/content/aip/journal/bmf/7/4/10.1063/1.4817006
10.1063/1.4817006
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