Biomolecular motor-driven microtubule translocation in the presence of shear flow: analysis of redirection behaviours

We suggest a concept for powering microfluidic devices with biomolecular motors and microtubules to meet the demands for highly efficient microfluidic devices. However, to successfully implement such devices, we require methods for active control over the direction of microtubule translocation. While most previous work has employed largely microfabricated passive mechanical patterns designed to guide the direction of microtubules, in this paper we demonstrate that hydrodynamic shear flow can be used to align microtubules translocating on a kinesin-coated surface in a direction parallel to the fluid flow. Our evidence supports the hypothesis that the mechanism of microtubule redirection is simply that drag force induced by viscous shear bends the leading end of a microtubule, which may be cantilevered beyond its kinesin supports. This cantilevered end deflects towards the flow direction, until it is subsequently bound to additional kinesins; as translocation continues, the process repeats until the microtubule is largely aligned with the flow, to a limit determined by random fluctuations created by thermal energy. We present statistics on the rate of microtubule alignment versus various strengths of shear flow as well as concentrations of kinesin, and also investigate the effects of shear flow on the motility.