Tolerances in microfluidic master molds: a comparison of 3D printing and micromilling

3D printing and micromilling are increasingly becoming more accessible alternatives to cleanroom photolithography for the fabrication of master molds that can be subsequently used for cast patterning soft material microfluidic devices. However, there is a lack of characterization on the fabrication tolerances of 3D printed and micromilled master molds, which can influence microdevice performance. In this work, we present an in-depth characterization of master molds fabricated using 3D printing versus micromilling. We utilized profilometry to examine the accuracy of fabricated channel dimensions and assess surface finish. We then proceed to assess differences in performance between devices cast from 3D printed or micromilled master molds by creating microfluidic splitting devices or flow focusing devices. We then evaluated their performance in a low-flow rate splitting application and in the generation of gelatin microspheres respectively. For both applications micromilling resulted in a significantly smoother surface finish when compared to 3D printed master molds. On average, both fabrication modalities fell short in accurately fabricating channel dimensions (∼50 µm) when compared to the original CAD model of the microfluidic master mold. In our low-flow rate application, there were no significant differences in flow rate splitting efficiency between microfluidic devices cast from either 3D printed or micromilled master molds. In our assay for generating gelatin microspheres, the smoother surface finish of the CNC master molds resulted in a flow focusing devices that generated significantly larger gelatin microspheres. Overall, this investigation serves as a useful guide for future investigators on the fabrication tolerances of soft material microfluidic devices cast from 3D printed and micromilled master molds.