PDMS-Parylene Hybrid, Flexible Microfluidics for Real-Time Modulation of 3D Helical Inertial Microfluidics

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.

Flexible Microfluidics: Fundamentals, Recent Developments, and Applications

“…Parylene is a thermoplastic polymer that has been employed for the fabrication of flexible microfluidics [84]. Taking advantage of flexibility, biocompatibility, and low water absorption, parylene-based flexible microfluidic devices with biomedical applications such as injection tools, neural probes [85][86][87], implantable 3D electrodes for drug delivery [88], tunable microfluidic lens arrays [89], and inertial separators [90] have been produced. Flexibility of parylene can enable the implanted microdevices to follow the deformation of the tissue.…”

“…Although parylene has a higher Young's modulus compared to PDMS, it can be formed as an ultrathin film, thereby reducing the bending stiffness. For instance, in some flexible microfluidic devices, a thin perylene layer deposited on thin PDMS microchannels offers excellent flexibility while still rigid enough to retain the cross-sectional shape of the microchannels [90].…”

“…The second technique for fabricating 3D flexible spiral microchannels is making planar 2D microchannels and then coiling them around a rod into 3D structures (Figure 9a) [172]. Also, Jung et al [90] have proposed an interesting method in producing 3D microchannels by simply bending a flexible planer microfluidic channel (Figure 9b). This method further provides the possibility of adjusting the channel curvature and therefore tuning the Dean flow inside the flexible microchannels.…”

“…Adapted with permission from Asghari et al [172]; (b) Bending a flexible planar microfluidic channel. Adapted with permission from Jung et al[90].…”

Rapid Prototyping of Polymer-Based Rolled-Up Microfluidic Devices

“…To date, only one prior rolled-up microfluidic device by which the microchannels were made by rolling PDMS-parylene thin films has been reported in the literature [ 25 ]. However, the method used was a chemical vapor deposition technique (CVD), which would not be suitable for large scale microfluidic systems or mass production of the devices, as the size of the CVD machine will limit the scale of the device.…”