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Research Papers

Dynamics of Cilia-Based Microfluidic Devices

[+] Author and Article Information
J. Kongthon

Mechanical Engineering Department,  University of Washington, Seattle WA 98195-2600jiradech@u.washington.edu

J.-H. Chung

Mechanical Engineering Department,  University of Washington, Seattle WA 98195-2600jae71@u.washington.edu

J. J. Riley

Mechanical Engineering Department,  University of Washington, Seattle WA 98195-2600rileyj@u.washington.edu

S. Devasia1

Mechanical Engineering Department,  University of Washington, Seattle WA 98195-2600devasia@u.washington.edu

1

Corresponding author.

J. Dyn. Sys., Meas., Control 133(5), 051012 (Aug 22, 2011) (11 pages) doi:10.1115/1.4004063 History: Received September 01, 2010; Revised March 01, 2011; Published August 22, 2011; Online August 22, 2011

This article models the dynamics of cilia-based devices (soft cantilever-type, vibrating devices that are excited by external vibrations) for mixing and manipulating liquids in microfluidic applications. The main contribution of this article is to develop a model, which shows that liquid sloshing and the added-mass effect play substantial roles in generating large-amplitude motion of the cilia. Additionally, experimental mixing results, with and without cilia, are comparatively evaluated to show more than one order-of-magnitude reduction in the mixing time with the use of cilia.

FIGURES IN THIS ARTICLE
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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematics of experiment for evaluating the frequency response of cilia. (a) Experimental setup; (b) image of a cilium in water excited by the piezoactuator; (c) input ub(t) and output y(t) motions of the cilium.

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Figure 2

Pressure gradient due to accelerating fluid generates buoyancylike force across the thickness of a cilium

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Figure 3

Schematic experimental setup (images not to scale) for evaluating the effects of added mass and sloshing on the frequency response of cilia. Case (a) the cilia are oscillated in air; case (b) the cilia are oscillated in water (inside a stationary, relatively large 60 mm × 115 mm chamber); and case (c) the chamber (3 mm diameter) containing the cilia is oscillated. In each case, three cilia are used.

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Figure 4

Frequency responses for three cases. The frequency responses of the fitted models are shown using solid lines, and experimental mean values (for three cilia in each case) are represented by dots. Case (a) the cilia are oscillated air; case (b) the cilia are oscillated in water (inside a stationary chamber); and case (c) the chamber containing the cilia is oscillated. The same set of cilia is used in case (a) and case (b) to capture the added-mass effect. The estimated added mass is used to model the cilia response with sloshing in case (c).

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Figure 6

Frequency responses for cilia in an oscillating chamber when the height of water is varied. Each data point (dot) represents the average value for the three cilia used in each experiment. The same cilia are used in all these experiments. The frequency responses of the fitted models are given by solid lines.

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Figure 10

Schematic setup of cilia device shown in Fig. 1 for mixing experiments in a 3 mm diameter chamber

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Figure 11

Sample images of the mixing process at different time instants t and corresponding mixing indices, Imix, as in Eq. 45: (a) with cilia, run 1 in Table 6; and (b) without cilia, run 1 in Table 6

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Figure 12

Time profiles of the mixing index Imix in Eq. 45 for seven experimental runs with cilia. The 90% mixing time is indicated with circles.

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Figure 13

Time profiles of the mixing index Imix in Eq. 45 for seven experimental runs without cilia. The 90% mixing time is indicated with circles.

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Figure 9

Oscillating chamber (case (c)): frequency responses for different-length cilia. Experimental values are represented by dots. Response of models with parameters fitted by least-squares error minimization is presented with solid lines. Dashed lines represent responses of predicted models.

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Figure 8

Stationary chamber (case (b)): frequency responses for different-length cilia. Experimental values are represented by dots. Responses of models with parameters fitted by least-squares error minimization is presented with solid lines.

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Figure 7

Variation of the sloshing natural-frequency ωsl with the ratio of the water height h to the chamber radius R. The dots represent the experimental data and the solid line represents the prediction by the fitted model in Eq. 42.

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Figure 5

Experimental frequency responses (mean value of three cilia) with and without sloshing, i.e., free surface is constrained from sloshing with a glass cover. The same set of three cilia was used for both experiments, with and without sloshing.

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