Fig. 5: Optogenetic control of the direction of the instability.

a Schematics of the light-dimerizable kinesin-1 motors. In the absence of light, the motors hydrolyze ATP, step on individual microtubules, but do not dimerize, which does not induce any relative sliding of the microtubules. When blue light is turned on (488 nm wavelength), the motors dimerize. Their stepping produces a net extension of the microtubule bundle. We shined pulsed patterns of blue light on a flow-aligned network; b for low blue light intensity, the network buckles out-of-plane; c for high blue light intensity, the network bends in-plane. In the absence of light, the network is stable and stays flow aligned; d Blurriness B of the unstable active network for varying light intensity (main: lin–lin plot, insert: lin–log plot showing the sharp transition around 0.1 µW/mm³). e Increasing the blue light pulses’ period induces a transition from in-plane bending to out-of-plane buckling for a critical pulse period \(\tau \sim 30\,{{{{{{\rm{s}}}}}}}\). The color map is the same for d, e and indicates the blurriness B. Error bars in d, e represent the standard deviation of the mean over N = 3 independent replicates. Experiments shown in b, c were, respectively, repeated N = 30 and N = 45 times. Source data are provided in the Source data file.