(100d) Two-Wavelength Volumetric 3D Printing for Rapid Fabrication of Multi-Level Microfluidic Networks

Conventional microfluidic fabrication faces multiple challenges which prevent scalable manufacturing. Microfluidic fabrication is often done using lithography, which results in long fabrication time and high costs, as well as confining the device to two-dimensional geometries. Recently, 3D printing has emerged as an effective solution to scale up microfluidic fabrication. However, 3D printing often involves discrete layer-by-layer steps, which result in slow print times and still limits the range of printable geometries. In this work, we demonstrate a novel volumetric 3D printing method for rapid fabrication of microfluidic networks. Our approach uses two wavelengths of light to generate simultaneous inhibition and initiation reactions in free-radical polymerized resins. (Meth)acrylic resins are formulated with a unique system of photoinitiator and photoinhibitor species such that irradiation by near UV light (365 nm) inhibits the polymerization reaction and irradiation of blue light (460 nm) initiates polymerization. Polymerization and inhibition models are calculated as a function of light dose and used to predict the depth of polymerization and inhibition. Superimposing UV light with patterned blue light enables spatial control of polymerization in three dimensions without a moving build platform.

Using this system, we fabricated microfluidic networks in less than 15 minutes. Initially, we used polymerization and inhibition models to calculate the necessary parameters, such as light dose, to print at various levels in the z-direction. Next, to print the networks, resin was filled between two glass slides to create a resin vat, and a sequence of UV and patterned blue exposures were projected into the resin vat. Finally, the print was post-treated by flushing uncured resin from the channels and irradiating the part with visible light, and the glass slides were removed to create a monolithic microfluidic network. The quality of the printed channels was investigated using optical profilometry. Our initial data suggests that we can control polymerization as far as 700 µm into the resin in the vertical z-direction. The profilometry results agree with our predictive models and illustrate the necessity of the models to print accurate geometries. Different geometries including multi-level serpentine mixing channels and vertically overlapping channels were printed. We successfully show that our system is well suited for rapid, low-cost, microfluidic fabrication in three dimensions. This technology represents a significant advance in both resolution and functionality over traditional lithography-based fabrication techniques which could dramatically lower the barrier-to-entry to explore microfluidic systems, thereby enabling accelerated microfluidic innovation and application.

Figure Caption: Schematic of the two-wavelength volumetric 3D printer.