Flow-pattern-altered syntheses of core–shell and hole–shell microparticles in an axisymmetric microfluidic device

Droplet-based microfluidics offers unique advantages to create platforms that fabricate functionalized particles with increased accessibility, robustness, and simplicity. Herein we present a three-phase microfluidic device that can control the flow pattern to directly generate either core–shell or hole–shell microparticles. The major benefits of this device are the ease of controlling the morphology of the compound droplets by the flow rates and thus the microstructure of the synthesized microparticles. The transition between flow patterns enables the generation of either core–shell particles or Janus particles in a single device. We further show the versatility of the proposed device in fabrication of functionalized particles: the hole size of the hole–shell microparticle can be fine-tuned while its outer diameter is kept constant, and by adding Fe3O4 nanoparticles into the photocurable phase, the obtained magnetoresponsive microparticle can move rotationally or translationally under an external magnetic field. We anticipate that the present method could facilitate the fabrication of the functional microparticles for diverse applications.