Movie 8.

Simulation of Hydra tissue mechanics during global activation of fiber contraction in a spheroid with a +1 defect and a pair of +1/2 defects. The movie depicts the results of simulations of a transient activation of global fiber contraction in a Hydra tissue spheroid with a nematic configuration containing a +1 defect on one side of the spheroid and a pair of +1/2 defects at the opposite end, emulating the actin fiber organization in regenerating fragments at later stages of the regeneration process (Fig. 5C). The tissue spheroid is modeled as a deformable shell that contains an embedded nematic field that experiences a time-dependent global activation of contraction (bottom graph). The images show cell segmentation maps depicting cells colored according to the cell area strain defined as ε_c = ln(A_c/A_c^ref), where A_c is the cell area and A_c^ref is the initial cell area, overlaid with lines indicating the orientation of the embedded nematic field in each cell. The spheroid is shown from a top view centered on the aster-shaped +1 defect, and a bottom view showing the pair of +1/2 defects. The active stress generated within each cell is aligned with the nematic field in that cell, and global activation leads to efficient mechanical strain focusing at the +1 defect site (right), and to a lesser extent at the pair of +1/2 defects (left).