Time-efficient fabrication method for 3D-printed microfluidic devices

Recent developments in 3D-printing technology have provided a time-efficient and inexpensive alternative to the fabrication of microfluidic devices. At present, 3D-printed microfluidic systems face the challenges of post-processing, non-transparency, and being time consuming, limiting their practical application. In this study, a time-efficient and inexpensive fabrication method was developed for 3D-printed microfluidic devices. The material for 3D-printed microfluidic chips is Dowsil 732, which is used as a sealant or encapsulant in various industries. The curing time and surface hydrophobicity of the materials were evaluated. The results indicated that the surface of Dowsil 732 is hydrophilic. An optimization model of the direct ink writing method is proposed to establish a time-efficient and accurate fabrication method for microfluidic devices. The results indicate that the optimization model can effectively describe the change trend between printing speed, printing pressure, and channel wall accuracy, and the model accuracy rate exceeds 95%. Three examples—a micromixer, concentration gradient generator, and droplet generator—were printed to demonstrate the functionality and feasibility of the fabrication method.

Microfluidic equipment¹ has the characteristics of small size, low cost, fast response, and high detection sensitivity², and it has been widely used in many fields, such as biomedicine^3,4, chemical synthesis⁵, agricultural governance⁶, and environmental testing⁷. In recent years, with the rapid development of modern additive manufacturing techniques, three-dimensional (3D)-printing technology has become a promising method for microfluidic device fabrication. Compared with traditional micro processing technologies, such as soft lithography⁸, computer numerical control milling^9,10, laser cutting^11,12, and injection molding¹³, 3D-printing technology has the advantages of rapid manufacturing¹⁴, wide material adaptability¹⁵, and low cost¹⁶. The 3D-printing technology provides a potential low-cost and time-saving alternative to conventional polydimethylsiloxane (PDMS) microfluidic systems, simplifies the traditional manual fabrication process, and reduces the need for professional microfabrication¹⁷.

At present, the best candidates or microfluidic devices through 3D-printing technology are stereolithography (SLA)^18,19, digital light projection (DLP)^20,21, fused deposition modeling (FDM)^22,23,24, and direct ink writing (DIW)^25,26. SLA and DLP are based on the selective curing of a photosensitive polymer to print the desired structures. The microfluidic devices produced by SLA printing technology have the advantage of high precision^27,28, but the photosensitive resin materials may remain in the micro channel, causing blockage inside the channel²⁹. In addition, the preprocessing and post-processing of microfluidic devices can result in a relatively complicated and time-consuming manufacturing process³⁰. The FDM or DIW printing technology is mainly based on the material extrusion method, and the fabrication process is relatively accessible. The printers for the FDM method are much more accessible because of their low prices. Compared with the SLA or DLP methods, the FDM or DIW method provides a wider material selection^31,32,33. Biocompatible and inexpensive polymer materials, such as poly lactic acid^34,35, acrylonitrile butadiene styrene^36,37, and NinjaFlex (flexible material)^38,39 make the FDM method an ideal candidate for 3D printing of microfluidic devices. However, most microfluidic devices using the FDM method are nontransparent or semitransparent, making them unsuitable for observation or optical detection.

Here, a time-efficient, inexpensive DIW method is proposed for the 3D printing of microfluidic devices. A microfluidic chip with a complex structure can be manufactured within one hour. The material for 3D-printed microfluidic chips is Dowsil 732 from Dow Corning (Midland, MI, USA). Similar to PDMS, Dowsil 732 is used as a sealant or encapsulant in many industries. However, no research related to the Dowsil 732 microfluidic device has been reported. In this work, first, the curing time and surface hydrophobicity of Dowsil 732 were evaluated, proving its suitability for the fabrication of microfluidic devices. To ensure that a high-precision micro channel structure can be obtained, the influence of printing pressure and printing speed on the accuracy of the channel wall were investigated, and a printing parameter optimization model was established based on measured data. Then, the accuracy between the micro channel design size and the actual printed size was examined further. Finally, three printing examples (a micro mixer, concentration gradient generator, and droplet generator) were used to verify the feasibility of the research theory.