Dissecting fat-tailed fluctuations in the cytoskeleton with active micropost arrays*

The actomyosin cytoskeleton is critical to a wide range of cellular mechanobiology and mechanotransduction. However, the understanding of the connections between molecular-scale processes and cell-scale mechanical phenomena is not complete. Using active micropost array detectors containing magnetic actuators, we have characterized the mechanics and fluctuations of cells’ actomyosin cortex and stress fiber networks in detail. Both structures show consistent power law viscoelastic behavior and highly intermittent fluctuations with fat-tailed amplitude distributions. In the cortex, the dynamics are dominated by occasional large events, similar to what is seen in earthquakes or systems with avalanches. We have observed this behavior across multiple cell types and substrate stiffnesses, and the regular arrays of microposts enable measurement of the largest events’ symmetry and extent (up to several micrometers), revealing spatiotemporal dynamics resembling that seen in plastic solids. These results suggest that actomyosin components may self-organize into marginally stable plastic networks that give cells their unique biomechanical properties.