Collective dynamics of microtubule-based 3D active fluids from single microtubules

Abstract

Self-organization of kinesin-driven, microtubule-based 3D active fluids relies on the collective dynamics of single microtubules. However, the connection between macroscopic fluid flows and microscopic motion of microtubules remains unclear. In this work, the motion of single microtubules was characterized by means of 2D gliding assays and compared with the flows of 3D active fluids. While the scales of the two systems differ by ~1,000×, both were driven by processive, non-processive or an equal mixture of both molecular motor proteins. To search for the dynamic correlation between both systems, the motor activities were tuned by varying temperature and ATP concentration, and the changes in both systems were compared. Motor processivity played an important role in active fluid flows but only when the fluids were nearly motionless; otherwise, flows were dominated by hydrodynamic resistance controlled by sample size. Furthermore, while the motors' thermal reaction led active fluids to flow faster with increasing temperature, such temperature dependence could be reversed by introducing temperature-varying depletants, emphasizing the potential role of the depletant in designing an active fluid's temperature response. The temperature response of active fluids was nearly immediate (≲10 sec). Such a characteristic enables active fluids to be controlled with a temperature switch. Overall, this work not only clarifies the role of temperature in active fluid activity, but also sheds light on the underlying principles of the relationship between the collective dynamics of active fluids and the dynamics of their constituent single microtubules.

Programmed mechano-chemical coupling in reaction-diffusion active matter

“…The velocity of the flow was estimated to be v m = 8 μm/min, which, considering the typical size of a fluid vortex, l m ≈ 125 μm, and the diffusion coefficient of DNA A , D A = 12 × 10 3 μ m 2 /min, yields a Péclet number Pe = v m l m / D A ≈ 0.08 (Supplementary Text). Note, however, that kinesin/microtubule active gels may reach flows up to 600 μm/min ( 43 ), which would result in Pe ≈ 5 and thus in a substantial perturbation of the front by the flow. Such large flows were not observed here.…”

Cancer: A turbulence problem

“…The macroscopic fluid transitions were characterized by Boltzmann-Gibbs distributions as would equally apply to the transitions in the metastable cell states of the Waddington attractor landscape. The critical Reynolds number was shown to be in the order of ∼60 to 100 for Taylor-Couette and Rayleigh-Benard convection systems, which is relatively feasible at biologically relevant scales [66 , 67] . Recall that the Reynolds number is an ill-defined parameter.…”

Cancer: A Turbulence Problem

“…Furthermore, an emerging field of research deals with active turbulence in active matter systems such as cytoskeletal and bacterial suspensions (88)(89)(90)(91)(92). The Reynolds number at which fluid turbulence is observed is subjected to debate, especially due to the investigating in active matter systems.…”