Defining Operational Limits of Low-Cost MSLA 3D Printing for Microfluidic Systems: Resin Performance, Cell Compatibility, and Fluid Dynamics.

Additive manufacturing using low-cost masked stereolithography technology is an attractive option to democratize microfluidic devices fabrication, albeit with limits in spatial resolution, optical transparency, cytotoxicity, and replication that need to be addressed. In this work, five transparent masked stereolithography resins employed in an Anycubic Photon M7 Pro low-cost printer are systematically studied to address the limitations mentioned above. The working route was based on the analysis of the dimensions of negative and positive microfeatures, their transmission spectra, their cytotoxicity, the capability of building internal channels, replicability in PDMS, and validation by computational fluid dynamics simulations with experimental fluid assays. Resolution tests revealed that negative structures resolved less accurately due to subtle resin accumulation during the layer-by-layer printing process. Internal channel fabrication showed a practical lower limit of approximately 500 μm under the printing and postprocessing conditions used in the study, with resin viscosity, printing angle, and drainage behavior strongly influencing channel clearance. The Standard V2 and High Clear resins exhibited the highest printing resolution with microchannels printed in a vertical or almost-vertical position. Regarding thermally cured PDMS replication, the Tough Ultra, ABS-like Pro 2, and Water-Wash were the ones exhibiting the most accurate outcome. From a biological point of view, all resins were non-cytotoxic, with Standard V2 and High Clear exhibiting the highest cell viability, in some cases better than the control scenario. Contact angle measurements indicated that the Standard V2 and High Clear resins are highly hydrophilic, whereas the remaining resins exhibit a hydrophobic behavior. Swelling was found to be dependent on the media, where the Water-Wash found high swelling in Milli-Q water and PBS and the Tough Ultra in ethanol. Samples were only minimally affected by isopropyl alcohol. Finally, fluid flow assays were conducted on three different microfluidic chips to demonstrate that the introduction of microfeatures and zigzag architectures fosters the disruption of laminar flow conditions by introducing secondary flows and vorticity to mimic more physiological environments. These experiments were contrasted with simulations performed by computational fluid dynamics. It was verified that microfeatures can be adequately implemented in the chip architecture and result in enhanced mixing. This validation allowed defining a practical operating window for MSLA 3D printers for microfluidics.