While there is great interest in 3D printing for microfluidic device fabrication, to-date the achieved feature sizes have not been in the truly microfluidic regime (<100 μ m). In this paper we demonstrate that a custom Digital Light Processor stereolithographic (DLP-SLA) 3D printer and a specifically-designed, low cost, custom resin can readily achieve flow channel cross sections as small as 18 μ m × 20 μ m. Our 3D printer has a projected image plane resolution of 7.6 μ m and uses a 385 nm LED, which dramatically increases the available selection of UV absorbers for resin formulation compared to 3D printers with 405 nm LEDs. Beginning with 20 candidate absorbers, we demonstrate the evaluation criteria and process flow required to develop a high-resolution resin. In doing so, we introduce a new mathematical model for characterizing the resin optical penetration depth based only on measurement of the absorber’s molar absorptivity. Our final resin formulation uses 2-nitrophenyl phenyl sulfide (NPS) as the UV absorber. We also develop a novel channel narrowing technique that, together with the new resin and 3D printer resolution, enables small flow channel fabrication. We demonstrate the efficacy of our approach by fabricating 3D serpentine flow channels 41 mm long in a volume of only 0.12 mm3, and by printing high aspect ratio flow channels <25 μ m wide and 3 mm tall. These results indicate that 3D printing is finally positioned to challenge the pre-eminence of methods such as soft lithography for microfluidic device prototyping and fabrication.

We report a noncytotoxic resin compatible with and designed for use in custom high-resolution 3D printers that follow the design approach described in Gong et al., Lab Chip 17, 2899 (2017). The noncytotoxic resin is based on a poly­(ethylene glycol) diacrylate (PEGDA) monomer with avobenzone as the UV absorber instead of 2-nitrophenyl phenyl sulfide (NPS). Both NPS-PEGDA and avobenzone-PEGDA (A-PEGDA) resins were evaluated for cytotoxicity and cell adhesion. We show that NPS-PEGDA can be made effectively noncytotoxic with a postprint 12 h ethanol wash, and that A-PEGDA, as-printed, is effectively noncytotoxic. 3D prints made with either resin do not support strong cell adhesion in their as-printed state; however, cell adhesion increases dramatically with a short plasma treatment. Using A-PEGDA, we demonstrate spheroid formation in ultralow adhesion 3D printed wells, and cell migration from spheroids on plasma-treated adherent surfaces. Given that A-PEGDA can be 3D printed with high resolution, it has significant promise for a wide variety of cell-based applications using 3D printed microfluidic structures.