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. Here, we characterize the motion of single microtubules through 2D gliding assays, compared with flows of 3D active fluids. While scales of both dynamics differ by ~1,000×, both are driven by either processive, non-processive or an equal mixture of both molecular motor proteins.
To search for the dynamic correlation between both systems, we tuned the motor activities by varying temperature and ATP concentration, while comparing the changes in both systems. We find that motor processivity plays an important role in active fluid flows but only when the fluids are nearly quiescent; otherwise, the flows are dominated by hydrodynamic resistance controlled by sample sizes. Furthermore, while the motor’s thermal reaction leads active fluids to flow faster with increasing temperature, we find that such a temperature dependence can be reversed through introducing temperature-varying depletants, emphasizing the role of the depletant in designing an active fluid’s temperature response.
Aside from fundamental interests, we demonstrate that the temperature response of active fluids is nearly immediate (≲10 sec). Such a characteristic enables controlling active fluids with a temperature switch. Overall, our work not only presents the role of temperature in active fluid activities but also sheds light on the underlying principles of the collective dynamics of active fluids from single microtubules.
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