Global order and lane formation in Microtubule-based active matter*

Kinesin motor proteins convert chemical energy into mechanical energy, moving throughout the cell to transport cargo by “walking” on microtubules (MTs). MTs are vital components of all Eukaryotic cells. They form part of the cytoskeleton and are important for cell division, and intracellular transport. In this project, we investigated MT-kinesin-based transportation by performing experiments using kinesin motors coupled to a lipid bilayer. We take advantage of the microtubule gliding assay configuration to probe collective behavior in dense MT swarms. On a glass substrate, kinesin motors adhere and are immobile, while MTs glide on them. MT behavior with fixed motors at high MT concentration is compared with their behavior on diffusing motor proteins at similar concentrations. We used a lipid bilayer similar to that in a cell to observe the MT behavior on membrane diffusing kinesins. The MTs exhibit collective motion with orientational order on different lengthscales, sensitive to MT density. Notably, at intermediate MT densities, we were able to observe apolar lane formation and characterize the differences in local and global order parameters.