Hydrogel impeller formation via vacuum degassing photopolymerization for micromixers

Abstract

For effective mixing within microfluidic devices through the application of obstacle-based structures, a straightforward approach involves in-situ fabrication, such as the free-radical photopolymerization of hydrogel structures. However, oxygen inhibition presents a challenge for polydimethylsiloxane (PDMS)-based microfluidic chips. In this paper, we present a solution to the problem of hydrogel-structure formation hindered by oxygen inhibition at low light intensities and the photoinitiator concentration achieved using vacuum degassing. Furthermore, a kinetic model for photopolymerization under vacuum conditions was established and converted into an equation of light intensity and exposure time while keeping the other parameters constant. The exposure time range was successfully predicted by comparing the experimental data and analyzing scenarios. This method was used to fabricate an impeller for a passive micromixer. The impeller rotation was then analyzed. The results demonstrated that with an increased flow rate exceeding 6 mL/min, the mixing efficiency is significantly higher owing to the rotation of the impeller. The mixing efficiency was quantitatively assessed through experiments involving the mixing of three dyes, showing a three-fold increase compared to the chip without the impeller. Our research provides valuable insights into the fabrication of hydrogel structures in PDMS-based microfluidic chips under vacuum conditions.