Evaluation of peristaltic micromixers for highly integrated microfluidic systems

Abstract

Microfluidic devices based on the multilayer soft lithography allow accurate manipulation of liquids, handling reagents at the sub-nanoliter level, and performing multiple reactions in parallel processors by adapting micromixers. Here, we have experimentally evaluated and compared several designs of micromixers and operating conditions to find design guidelines for the micromixers. We tested circular, triangular, and rectangular mixing loops and measured mixing performance according to the position and the width of the valves that drive nanoliters of fluids in the micrometer scale mixing loop. We found that the rectangular mixer is best for the applications of highly integrated microfluidic platforms in terms of the mixing performance and the space utilization. This study provides an improved understanding of the flow behaviors inside micromixers and design guidelines for micromixers that are critical to build higher order fluidic systems for the complicated parallel bio/chemical processes on a chip.

FIG. 1.

Schematic diagrams of pneumatically controlled microfluidic devices. (a) Simple on-off valve and (b) peristaltic micro pump (not to scale).

FIG. 2.

Layout of the mixer chip (chip B); blue lines, yellow lines, and red lines represent the flow channels, the control channels connected to shutoff valves, and the control channels connected to mixing valves, respectively.

FIG. 3.

Mixer chip designs. (a) Angle variation of mixing valves; the central angle is proportional to the distance between the mixing valves (mixing valve width: 200 μm). (b) Width variation of mixing valves; distance between the mixing valves is equivalent to that of the mixer whose central angle between the mixing valves and mixing valve width is 45° and 200 μm. (c) Shape variation of mixing loop; distance between the mixing valves is equivalent to that of the circular mixer whose central angle between the mixing valves is 30° (mixing valve width: 200 μm).

FIG. 4.

Experimental setup and fabricated mixer chip (chip D); all channels of the mixer chip are filled with food dyes (flow channels: blue; control channels connected to shutoff valves: green; control channels connected to mixing valves: red) to show the planar configuration of the fabricated mixer chip.

FIG. 5.

Effect of pressurizing mixing valves on mixing performance; when compared with water (filled circles) which is used to pressurize the mixing valves, nitrogen gas (hollow circles) reduces the mixing time (loop shape: circle; angle between mixing valves: 30°; mixing valve width: 200 μm).

FIG. 6.

Mixing phenomena in a mixer chip. (a) Mixing by molecular diffusion; boundary layer thickness increases to about 200 μm in 1 min. (b) Active mixing by mixing valve operation; mixing is completed within 4 s. (c) Quantification of the degree of mixing using the average gray value for the mixer area (hatched region); the average gray value decreases to a steady state value as the mixing progresses. (d) Mixing index using the average gray value; the mixing index increases from 0 to 1 as the mixing progresses (loop shape: circle; angle between mixing valves: 10°; mixing valve width: 200 μm; operating pressure: 15 psi; operating frequency: 13 Hz).

FIG. 7.

Effect of operating frequency on mixing performance: the mixing index increases more rapidly when the operating frequency is 13 Hz regardless of the mixing loop shape.

FIG. 8.

Summary of parametric study. Effect of the distance between neighboring mixing valves on (a) degree of mixing and (b) hydrodynamic mixing enhancement. Effect of mixing valve width on (c) degree of mixing and (d) hydrodynamic mixing enhancement. Effect of mixing loop shape on (e) degree of mixing and (f) hydrodynamic mixing enhancement.