Control and characterization of microtubule kinesin active fluid behavior

Bate, Teagan

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Control and characterization of microtubule kinesin active fluid behavior

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The field of active matter is striving to make real connections with cell biology and develop useful materials. Microtubule kinesin active fluid is an active matter platform that provides an opportunity to advance our capabilities in in-vitro purified cytoskeletal active materials and cell simulations. The techniques of control and characterization we establish in this system create a vocabulary and fluency that will enable the engineering of new active matter systems to simulate biological phenomena and craft new functional materials. In addition, microtubule kinesin active fluid may yet shed light on the self-organization of diffusive and advective transport behavior in the crowded, active, and many-constituent cytoplasm, while continuing to reveal new characterization and control techniques. The work described in this dissertation expands these techniques of control and characterization, and provides new insight connecting kinesin kinetics, diffusion, and advection in the context of active cytoskeletal fluid. In our first investigation, we explore the relationship of kinesin kinetics at the nanoscale to active fluid flow at the mesoscale. We control the mean speed of both gliding assays and active fluid with temperature. By measuring the activation energy from the velocity temperature profiles, we connect mesoscale fluid activity to nanoscale kinesin kinetics to understand their role in both 2D gliding assays and 3D active fluids. Next, we investigate how flow couples to diffusional and advective mixing in active fluid. Having established temperature as an effective technique to control mean speed temporally, we show how to control mean speed spatiotemporally by applying temperature gradients to active fluid and investigate if such mean speed gradients can enhance mixing. Next, we use light-released ATP to induce mean speed gradients. We find that as spatially released ATP spreads through samples, activity spreads with it, creating a propagating active-passive interface. Considering this evolution from a non-uniform to uniform activity as mixing, we find that the interface progression undergoes a transition from regular to super diffusive-like spreading at a critical Peclét number. These works highlight the advancement of control and characterization techniques for microtubule kinesin active fluid and their associated intellectual merit which will inform the development of autonomous, limited self-assembling, controllable active materials, as well as supporting future investigations of the underlying mechanics of constituents and systems in living cells.

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