FIG. 4.

Contracting gel: Contractions yield nematic alignment and surface roughening. (a) z-projected images demonstrate that decreasing network volume leads to increasing nematic alignment. (b) z projection of the microtubule nematic order. Hue indicates the nematic director indicated by the color wheel, while intensity indicates coherency (Supplemental Material [32]). (c) The microtubule nematic order parameter increases during contraction and then decreases during roughening. (d) The contracting network’s volume (solid purple line) decreases continuously. Its surface area (dashed black line) initially decreases but then increases. (e) A 10 μm z projection of the material after surface roughening generates spherical cavities. (f) A cropped 3D projection highlights the invaginated structure of the microtubule network. (g) x-y and z-y show a hemispherical cavity. The sample is composed of 10 μM tubulin (black) and 200 nM kinesin (blue).