Fig. 3.

Formation of nematic wedges at high filaments’ density. (A) Structures forming at 1 μm bulk actin. (B) Close-up of locally forming +1/2 (Left) and −1/2 (Right) topological defects. The local alignment of filaments is also shown, with a mismatch present in the core of the defect. Positive defects up-concentrate filaments, whereas negative ones are empty. (C) Formation of a comet-like stream emerging from a +1/2 defect. The intensity profile along the dashed line is also plotted, showing the accumulation and then motion of the comet. Gray profile is the profile at the initial time as a reference. (D) Scheme of the nematic wedge-based polarity sorting. If a wedge is formed by a preexisting stream (orange), filaments (blue) get trapped inside it unable to escape and accumulate, forming locally a +1/2 defect. Filaments with opposite polarity (green) are able to escape. Thus, the polarity of filaments is locally sorted. When the obstacle is removed, filaments are now free to move again and form a comet-like stream. (Scale bars in A–C, 10 μm.)