Viscoelastic properties of microtubule networks

Microtubules are filamentous protein biopolymers found in eukaryotic cells. They form networks that guide active intracellular transport and support the overall cell structure. Microtubules are very rigid polymers, with persistence lengths as large as a millimeter. As such, they constitute an example of rodlike polymers, whose mechanical and rheological properties are as yet poorly understood. We measure the linear and nonlinear viscoelastic properties of isotropic solutions of purified microtubules, as well as networks permanently cross-linked with biotin-NeutrAvidin. In the linear regime both solutions and networks are soft elastic materials with elastic moduli on the order of a few pascals. The elastic moduli show a power-law dependence on tubulin concentration, c