Design and Rapid Prototyping of 3D-Printed Microfluidic Systems for Multiphase Flow

Since the emergence of microfluidic devices, subtractive manufacturing techniques have dominated their production. Although the conventional manufacturing processes are well established, they come along with some disadvantages that limit the accessibility and hinder the further development of microfluidics. With the rise of additive manufacturing, researchers are focused on developing alternative fabrication methods to promote affordability and accessibility. This paper presents the opportunities and challenges of laser-based stereolithography printers for the fabrication of microfluidic equipment. Emphasis is put on the design and iterative prototyping process from the initial design idea to the final device. To print with adequate and sufficient geometrical accuracy and suitable material, the optimization of the printer’s performance is discussed. Regarding the design of multiphase microfluidics and its complex fluid behavior, suitable surface treatments, including an appropriate cleaning protocol, and coating strategies to make the printed channels either hydrophilic or hydrophobic are presented to ensure applicability. With these fundamentals of additive manufacturing in microfluidic fabrication at hand, the second focus of this contribution is on the application of a modular co-flow device and a monolithic flow-focusing device to generate droplets and slugs in different multiphase flow applications. The presented co-flow setup features a tapered capillary that affects the droplet and slug sizes due to differing diameters, with larger diameters leading to larger droplets and slugs and vice versa. Several design parameters for the flow-focusing device were evaluated to determine the influence of device design on multiphase flow formation. It was found that the diameter of the inlet for the dispersed phase has the greatest effect on the size of the resulting droplets and slugs and covers the largest range of adjustable sizes.