High-Precision Stereolithography of Biomicrofluidic Devices.

Stereolithography (SL) is emerging as an attractive alternative to soft lithography for fabricating microfluidic devices due to its low cost and high design efficiency. Low molecular weight poly(ethylene glycol)diacrylate (MW = 258) (PEG-DA-258) has been used for SL 3D-printing of biocompatible microdevices at submillimeter resolution. However, 3D-printing resins that simultaneously feature high transparency, high biocompatibility, and high resolution are still lacking. It is found that photosensitizer isopropyl thioxanthone can, in a concentration-dependent manner, increase the absorbance of the resin (containing PEG-DA-258 and photoinitator Irgacure-819) by over an order of magnitude. This increase in absorbance allows for SL printing of microdevices at sub pixel resolution with commercially available desktop printers and without compromising transparency or biocompatibility. The assembly-free, rapid (<15 h) 3D-printing of a variety of complex 3D microfluidic devices such as a 3D-fluid router, a passive chaotic micro-mixer, an active micro-mixer with pneumatic microvalves, and high-aspect ratio (37:1) microchannels of single pixel width is demonstrated. These manufacturing capabilities are unavailable in conventional microfluidic rapid prototyping techniques. The low absorption of small hydrophobic molecules and microfluidic labeling of cultured mammalian cells in 3D-printed PEG-DA-258 microdevices is demonstrated, indicating the potential of PEG-DA-based fabrication of cell-based assays, drug discovery, and organ-on-chip platforms.

3D-printed Quake-style microvalves and micropumps.

Here we demonstrate a 3D-printable microvalve that is transparent, built with a biocompatible resin, and has a simple architecture that can be easily scaled up into large arrays. The open-at-rest valve design is derived from Quake's PDMS valve design. We used a stereolithographic (SL) 3D printer to print a thin (25 or 10 µm-thick) membrane (1200 or 500 µm-diam.) that is pneumatically pressed (∼3-6 psi) over a bowl-shaped seat to close the valve. We used poly(ethylene diacrylate) (MW = 258) (PEG-DA-258) as the resin because it yields transparent cytocompatible prints. Although the flexibility of PEG-DA-258 is inferior to that of other microvalve fabrication materials such as PDMS, the valve benefits from the bowl design and the membrane's high restoring force since it does not need a negative pressure to re-open. We also 3D-printed a micropump by combining three Quake-style valves in series. The micropump only requires positive pressure for its operation and profits from the fast return to the valves' open states. Moreover, we printed a 64-valve array constructed with 500 µm-diam. valves to demonstrate the reliability and scalability of the valves. Overall, we demonstrate the 3D-printing of compact microvalves and micropumps using a process that precludes the need for specialized, time-consuming labor.