Effect of Microtubule Length on Topological Defect Dynamics and Morphology in Active Nematics*

Microtubules are dynamic polymers of tubulin subunits that comprise a major transport system of cells and aid in many cellular processes in conjunction with the kinesin motors that traverse the length of the microtubules. In-vivo, these motors "walk" along the tube usually carrying materials for transport. In-vitro gliding assay experiments bind one end of the motor to a substrate, allowing the microtubules to glide along a surface of motor proteins. In our work, instead the motor proteins functions as crosslinkers, with two heads connecting two microtubules instead of being anchored to a substrate. It has previously been shown that stabilized microtubules form a dynamic system in the presence of kinesin motors and ATP. Here the active matter is confined to a 2D oil-water interface and the kinesin motors promote the creation and annihilation of topological defects in the active nematic. Using fluorescence microscopy, we investigate the self-organization of GMPCPP stabilized microtubules into patterns in active nematic, looking to see how the resulting defect dynamics and morphologies vary as the length of microtubules is increased from 1 to 10 micrometers. Video image analysis allows us to measure Vrms and active length scale as a function of MT length.