Spatiotemporal mapping of non-equilibrium dynamics and mechanics in active cytoskeleton composites

Biological active matter, such as active cytoskeleton composites (ACCs), display rich non-equilibrium dynamics, structure and mechanical properties. For example, we have shown that kinesin motors can reorganize actin-microtubules composites into a range of morphologies, from connected filamentous networks to segregated amorphous clusters, that exhibit emergent stiffening and contractility. Here, we combine holographic optical tweezers (HOT) with differential dynamic microscopy (DDM) to characterize these heterogeneously structured ACCs over a wide range of spatiotemporal scales and kinesin concentrations. HOT enables precise control over an array of micro-probes, which act as spatially-resolved force sensors. Forces can be applied through motor activity within the composite, periodic straining of micro-probes positioned at the center of the array, or by patterned straining of the micro-probe array. To characterize the spatiotemporally varying filament dynamics and relaxation that map to the force response, we use space- and time-resolved DDM. This powerful approach allows for the discovery of emergent rheological and dynamical properties of ACCs and other active matter with exquisite sensitivity across a broad range of scales.