Abstract
We present a continuous-flow active micromixer based on channel-wall deflection in a polydimethylsiloxane (PDMS) chip for volume flows in the range up to 2 μL s−1 which is intended as a novel unit operation for the microfluidic Braille pin actuated platform. The chip design comprises a main microchannel connected to a series of side channels with dead ends aligned on the Braille pins. Computer-controlled deflection of the side-channel walls induces chaotic advection in the main-channel, which substantially accelerates mixing in low-Reynolds number flow. Sufficient mixing (mixing index MI below 0.1) of volume flows up to 0.5 μL s−1 could be achieved within residence times ~500 ms in the micromixer. As an application, continuous dilution of a yeast cell sample by a ratio down to 1:10 was successfully demonstrated. The mixer is intended to serve as a component of bio-analytical devices or as a unit operation in the microfluidic Braille pin actuated platform.
Highlights
Mixing of fluids in microchannels is challenging due to the stable laminar flow
We present a continuous-flow active micromixer based on channel-wall deflection in a polydimethylsiloxane (PDMS) chip for volume flows in the range up to μL s−1 which is intended as a novel unit operation for the microfluidic Braille pin actuated platform
Stretching and folding is a key indicator of chaotic advection, and this image sequence clearly shows the capability of the Braille-actuated micromixer to perform rapid fluid mixing
Summary
Mixing of fluids in microchannels is challenging due to the stable laminar flow. The speed of mixing is limited by molecular diffusion, and is inversely proportional to the size of the fluid molecule or particle to be mixed [1]. One profound phenomena for efficient microscale mixing is chaotic advection [4], which involves local stretching and folding of the fluid streams and results in significant reduction in effective diffusion length. Mixing in continuous-flow condition is challenging due to the lower speed of mixing compared to the typically short residence time of the particles in the mixer. Tabeling et al [4] reported a cross-channel micromixer which exploits chaotic motion of fluid particles in the main channel due to pressure perturbation at side channels. Such structures with robust and compact pressure-perturbation sources can be used for rapid mixing in microscale for continuous flow condition
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