Fabricating smooth PDMS microfluidic channels from low-resolution 3D printed molds using an omniphobic lubricant-infused coating
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The advent of 3D printing has allowed for rapid bench-top fabrication of molds for casting polydimethylsiloxane (PDMS) chips, a widely-used polymer in prototyping microfluidic devices. While fabricating PDMS devices from 3D printed molds is fast and cost-effective, creating smooth surface topology is highly dependent on the printer's quality. To produce smooth PDMS channels from these molds, we propose a novel technique in which a lubricant is tethered to the surface of a 3D printed mold, which results in a smooth interface for casting PDMS. Fabricating the omniphobic-lubricant-infused molds (OLIMs) was accomplished by coating the mold with a fluorinated-silane to produce a high affinity for the lubricant, which tethers it to the mold. PDMS devices cast onto OLIMs produced significantly smoother topology and can be further utilized to fabricate smooth-channeled PDMS devices. Using this method, we reduced the surface roughness of PDMS microfluidic channels from 2 to 0.2 μm (10-fold decrease), as well as demonstrated proper operation of the fabricated devices with superior optical properties compared to the rough devices. Furthermore, a COMSOL simulation was performed to investigate how the distinct surface topographies compare regarding their volumetric velocity profile and the shear rate produced. Simulation results showed that, near the channel's surface, variations in flow regime and shear stress is significantly reduced for the microfluidic channels cast on OLIM compared to the ones cast on uncoated 3D printed molds. The proposed fabrication method produces high surface-quality microfluidic devices, comparable to the ones cast on photolithographically fabricated molds while eliminating its costly and time-consuming fabrication process.
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