The characterization of SU-8 microchannels for electrokinetic microfluidic applications is reported. The electroosmotic (EO) mobility in SU-8 microchannels was determined with respect to pH and ionic strength by the current monitoring method. Extensive electroosmotic flow (EOF), equal to that for glass microchannels, was observed at pH ≥4. The highest EO mobility was detected at pH ≥7 and was of the order of 5.8 × 10⁻⁴ cm² V⁻¹ s⁻¹ in 10 mM phosphate buffer. At pH ≤3 the electroosmotic flow was shown to reverse towards the anode and to reach a magnitude of 1.8 × 10⁻⁴ cm² V⁻¹ s⁻¹ in 10 mM phosphate buffer (pH 2). Also the zeta-potential on the SU-8 surface was determined, employing lithographically defined SU-8 microparticles for which a similar pH dependence was observed. SU-8 microchannels were shown to perform repeatably from day to day and no aging effects were observed in long-term use.

Three-dimensional (3D) printing has recently emerged as a cost-effective alternative for the rapid prototyping of microfluidic devices. The feature resolution of 3D printing is particularly well suited for the manufacturing of continuous flow cell culture platforms. Poor cell adhesion or material-induced cell death may, however, limit the introduction of new materials to microfluidic cell culture. In this work, we characterized four commercially available materials commonly used in stereolithography-based 3D printing with respect to long-term (2-month) cell survival on native 3D printed surfaces. Cell proliferation rate, along with material-induced effects on apoptosis and cell survival, were examined in mouse embryonic fibroblasts. Additionally, the feasibility of Dental SG (material with the most favored properties) for culturing of human hepatocytes and human-induced pluripotent stem cells was evaluated. The strength of cell adhesion to Dental SG was further examined over a shear force gradient of 1-89 dyne/cm² by using a custom-designed microfluidic shear force assay incorporating a 3D printed, tilted and tapered microchannel sealed with a polydimethylsiloxane lid. According to our results, autoclavation of the devices prior to cell seeding played the most important role in facilitating long-term cell survival on the native 3D printed surfaces with the shear force threshold in the range of 3-8 dyne/cm².