Figure 4. Asymmetry-induced formation of contractile fibres.

(a) Time series of a contracting array with a free boundary perpendicular to the channel axis. The stimulated area (n=20 cycles) has an initial size of ≈100,000 μm². (b) Analysis of the whole images reveals the emerging orientation of actin structures parallel to the channel axis at 90°. Orientational distributions are shown for the 8 to a corresponding (colour coded) time points during the contraction. Inset: zoom into a yet uncontracted region reveals an apparently isotropic network, in agreement with the distribution at the starting point of stimulation (red line). (c) Zoom in after completed contraction: Red arrows denote increased alignment of actin structures as the result of motor activity and confinement of tension, quantitatively reflected by the peaked distribution (dark blue line).