Optical Tweezers Microrheology of Active Co-entangled Actin-Microtubule Networks*

Co-entangled actin-microtubule networks can serve as tunable substrates for self-driven motor proteins and facilitate mesoscale biological behavior such as mitosis, meiosis, cytoplasmic streaming, and regeneration in the in-vivo, non-equilibrium environment. In-vitro characterization of actin-microtubule networks have revealed tunable emergent mechanical properties differing from those of networks containing either component alone. However, how non-equilibrium, motor-driven activity impacts the mechanical response of actin-microtubule networks remains unknown. To address this gap, we perform nonlinear optical tweezers microrheology measurements on active actin-microtubule networks driven by the molecular motor myosin II. We characterize the mesoscale mechanical response of the non-equilibrium networks as a function of activity time and in varying locations throughout the networks to determine the spatial distribution of responses. Our methods are applicable to a wide range of active matter systems and our results establish guiding principles towards the creation of tractable bio-inspired active materials.