Abstract
Inertial microfluidics has drawn much attention for its applications for circulating tumor cell separations from blood. The fluid flows and the inertial particle focusing in inertial microfluidic systems are highly dependent on the channel geometry and structure. Flexible microfluidic systems can have adjustable 3D channel geometries by curving planar 2D channels into 3D structures, which will enable tunable inertial separation. We present a poly(dimethylsiloxane) (PDMS)-parylene hybrid thin-film microfluidic system that can provide high flexibility for 3D channel shaping while maintaining the channel cross-sectional shape. The PDMS-parylene hybrid microfluidic channels were fabricated by a molding and bonding technique using initiated chemical vapor deposition (iCVD) bonding. We constructed 3D helical inertial microfluidic channels by coiling a straight 2D channel and studied the inertial focusing while varying radius of curvature and Reynolds number. This thin film structure allows for high channel curvature and high Dean numbers which leads to faster inertial particle focusing and shorter channel lengths than 2D spiral channels. Most importantly, the focusing positions of particles and cells in the microchannel can be tuned in real time by simply modulating the channel curvature. The simple mechanical modulation of these 3D structure microfluidic systems is expected to provide unique advantages of convenient tuning of cell separation thresholds with a single device.
Highlights
Inertial microfluidics has attracted considerable attention due to its capability of high-throughput microparticle manipulation using simple device structures [1,2,3,4]
Among the various inertial microfluidic systems, spiral channels have been recognized by their superior performances owing to the size-dependent Dean drag force which leads to larger separation distances compared to straight channels [4,13,14,15]
We developed a fabrication process for a flexible, thin-film microfluidic system using PDMS and parylene (Figure 1)
Summary
Inertial microfluidics has attracted considerable attention due to its capability of high-throughput microparticle manipulation using simple device structures [1,2,3,4]. The understanding of the inertial focusing in spiral channels is still incomplete, and there is no simple guideline for achieving optimal device design and operating conditions for diverse separation targets. Due to the difficulty in the exact prediction of the inertial focusing within spiral channels, optimization of the separation efficiency requires empirical determination of the optimal device design and operating conditions for each application. Considering the number of parameters to be tested, it is impractical to find the best device design by varying all possible parameters It is still questionable if the performances of the spiral channels are fully optimized, even though they give reasonably satisfactory results for a particular sample. Thin-film parylene microfluidics with the film thickness as thin as a few micrometers can provide high flexibility to construct 3D channel structures with enough rigidity to maintain a cross-sectional shape against internal pressure and bending [16]. We demonstrate real-time tuning of inertial focusing and separation with modulation of the flexible microfluidic 3D structure
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