The invention relates to a microfluidic device for making a liquid/liquid or gas biphasic system using a first liquid or a gas and a second liquid, non-miscible with each other, the device having a first hydrophobic surface for the second liquid, the first liquid forming a layer (6) on said first hydrophobic surface. The device comprises means for introducing a drop (7) of the second liquid into the layer of first liquid or gas and in contact with said first hydrophobic surface, and means for displacing the drop on said first hydrophobic surface along a determined path, the device having on the path of the drop, at least one wetting defect causing, upon passing of the drop over this defect, failure of the triple line of contact of the drop on the first hydrophobic surface and inclusion of first liquid (8) or gas into the drop.The invention also relates to the associated method.