Spatiotemporal mapping of dynamics of active cytoskeleton composites

The cytoskeleton provides structural integrity to cells and plays a critical role in regulating essential mechanical processes. We reconstitute cytoskeletal composites which consist of actin filaments and microtubules along with kinesin motor proteins. These active cytoskeletal composites (ACCs) have been shown to exhibit spatiotemporal structural and mechanical heterogeneity. Here, we combine holographic optical tweezers microrheology with time-resolved differential dynamic microscopy (DDM) to characterize the complex dynamics of ACCs and spatiotemporally resolve their force response due to passive viscoelasticity and active stresses. Specifically, a grid of optically trapped microspheres serve as force sensors while time-dependent filament dynamics within ACCs are determined through time-resolved DDM. This platform is widely applicable to spatiotemporally mapping dynamics and mechanics of heterogeneous non-equilibrium systems. Our specific results show that increasing the concentration of kinesin motors enhances spatial heterogeneity and local stress generation, while simultaneously shortening the range of influence of the local stresses.