Abstract
Droplet generation has been widely used in conventional two-dimensional (2D) microfluidic devices, and has recently begun to be explored for 3D-printed droplet generators. A major challenge for 3D-printed devices is preventing water-in-oil droplets from sticking to the interior surfaces of the droplet generator when the device is not made from hydrophobic materials. In this study, two approaches were investigated and shown to successfully form droplets in 3D-printed microfluidic devices. First, several printing resin candidates were tested to evaluate their suitability for droplet formation and material properties. We determined that a hexanediol diacrylate/lauryl acrylate (HDDA/LA) resin forms a solid polymer that is sufficiently hydrophobic to prevent aqueous droplets (in a continuous oil flow) from attaching to the device walls. The second approach uses a fully 3D annular channel-in-channel geometry to form microfluidic droplets that do not contact channel walls, and thus, this geometry can be used with hydrophilic resins. Stable droplets were shown to form using the channel-in-channel geometry, and the droplet size and generation frequency for this geometry were explored for various flow rates for the continuous and dispersed phases.
Highlights
Microfluidic devices (MFDs) have emerged as highly versatile tools for a broad range of applications including biochemical analysis, biomedical assays and personalized medicine [1,2,3,4,5,6,7]
The second category includes 3D-printed non-planar microfluidic devices [9,11,12,13] at size scales ranging from the large microfluidic (100–500 μm) regime to the lower-resolution millifluidic (>1 mm) regime
The objectives of this research were (1) to develop a resin system sufficiently hydrophobic for droplets to be able to generated in a planar microfluidic devices (pMFD), and (2) to develop a 3D non-planar microfluidic devices (npMFD)
Summary
Microfluidic devices (MFDs) have emerged as highly versatile tools for a broad range of applications including biochemical analysis, biomedical assays and personalized medicine [1,2,3,4,5,6,7]. The first includes high-resolution planar microfluidic devices (pMFD) [8,9,10,11], made the traditional way using stereolithography to make a negative mold, filling the mold with polydimethylsiloxane (PDMS) resin, and covering the cured PDMS with glass to create fluid channels lying in the plane of the covering This type of device allows for high-resolution channels well within the microfluidic regime (1 mm) regime Such devices often have flow channels over and around each other in true 3D geometry.
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