Our understanding of domain positioning was finally applied to control more complex patterning of domain localization. We designed microfluidic chambers with a height h = 30 µm and periodically spaced 50 µm-diameter pillars distributed in a hexagonal or squared fashion (Figure , left) and applied a similar procedure of GUV confinement as with straight channels. Vesicles trapped between the pillars adopted the local geometry and displayed either 3 or 4 free regions for domain fusion according to the pillar arrangement (Figure , middle). As expected, the free regions defined by the area between the pillars dictated the localization of the minority phase, leading to controlled formation of tripolar and quadripolar GUVs, with well-positioned poles of Ld (Comp.1, Lo-rich) or Ld (Comp.2, Ld-rich) domains (Figure , right, Supplementary movie S3).