Formation of Shear Band in a Microtubule Solution

Abstract

Flow instability under shear flow is commonly observed in many soft-bio materials. This instability causes the formation of macroscopic band referred to as “shear bands”, which can be regarded as non-equilibrium phase transition. This shear band formation has been reported in a variety of systems, including DNA, polymer and surfactant systems. Very recently, we found that biological materials such as actin filament and microtubule systems show the shear band formation. These biological materials are a component of the cytoskeleton. It is interesting to know their mechanical instability under shear deformation because their structure formations are very important in a number of cellular processes. In this study, we directly visualize the shear deformation of a microtubule solution systems, and discuss the physical origin of the shear banding. Microtubule movement is characterized by dynamic instability and treadmilling. This non-equilibrium phenomena can be suppressed by adding microtubule stabilizing agent “Paclitaxel”. In the absence of paclitaxel, the shear band formation is not observed. In microtubule solution with paclitaxel, on the other hand, we observed the shear band formation at shear rate of 0.01-0.1 s−1, which roughly corresponds to cell migration speed. As the paclitaxel concentration is increased, the shear band formation is observed in wide shear rates. Rheological property of the microtubule may play a role in mechanical propagation of the force for the cell migration.