One-step wettability patterning of PDMS microchannels for generation of monodisperse alginate microbeads by in Situ external gelation in double emulsion microdroplets

Droplet-based microfluidic systems are promising tools for many biological applications from digitalized analysis to drug delivery and biomolecules synthesis. Among these, fabrication of microgels, particularly alginate microbeads, has substantial importance due to their capability for three-dimensional (3D) encapsulation of cells, drugs and other bioactive materials. However, biocompatible generation of monodisperse alginate microbeads is still challenging. In this study, a new droplet-based microfluidic strategy is developed for cell and chip friendly fabrication of monodispersed alginate microbeads. The polydimethylsiloxane (PDMS) microfluidic device is first treated using on-chip plasma-assisted deposition of polyvinyl alcohol, to selectively modify the hydrophobicity of microchannels. The proposed wettability patterning approach is permanent, simple, reliable, and time-effective, which makes the resulting microfluidic device highly stable and controllable for generation of double emulsions (DEs). The device is then used for fabrication of monodisperse alginate microbeads using external gelation in DE microdroplets. The reported microbead fabrication method offers both biocompatibility as a result of external gelation and rapid recovery of beads from processing solutions, as well as chip-compatibility due to clog-free gelation. This simple and robust DE strategy provides new opportunities not only for 3D micro-encapsulation but also for other droplet-based microfluidic applications in diagnostic testing and drug delivery.