Combining Hydrophilic and Hydrophobic Materials in 3D Printing for Fabricating Microfluidic Devices with Spatial Wettability

The fabrication of microfluidic flow cells via projection micro-stereolithography (P mu SL) has excited researchers in recent years. However, due to the inherent process properties of most commercial P mu SL, microfluidic devices are fabricated in a monolithic fashion with uniform material properties across a flow cell. Yet, the large surface-to-volume ratio in microfluidics demands to tailor microchannel surface properties-particularly in planar microchannel arrangements-with spatial control and micron-scale resolution to form a desired flow profile, e.g., emulsion droplets. The fabrication of planar microfluidic devices by P mu SLbased 3D printing with spatial control over surface properties is presented. For that, homemade photopolymer formulations being either hydrophilic or hydrophobic is designed. Adding acrylic acid to a resin containing poly(ethylene glycol) diacrylate lowers the contact angle down to 0 degrees against water creating a superhydrophilic surface. By utilizing 1H,1H,2H,2H-perfluorodecyl acrylate, a photopolymer formulation allowing for 3D-printing a hydrophobic microchannel surface with a contact angle >120 degrees against water is obtained. Combining these two materials, it is 3D-print microfluidic flow cells with spatially defined wettability for emulsion formation. Finally, the resin vat of the commercial P mu SL printer during the printing process for fabricating multimaterial geometries is switched, exemplarily applied for realizing a hydrophobic-hydrophilic-hydrophobic device for forming O/W/O double emulsions.

Automated summary

The fabrication of microfluidic flow cells using projection micro-stereolithography (PμSL) allows for precise control of surface properties to create desired flow profiles, such as emulsion droplets. Homemade photopolymer formulations are designed to create either hydrophilic or hydrophobic surfaces, enabling the 3D printing of microchannels with specific wettabilities. By combining these materials, it is possible to fabricate microfluidic flow cells with spatially defined wettability for emulsion formation.