Shear-induced gelation of self-yielding active networks*

The activity of molecular motors reconfigures biopolymer networks and modifies their mechanical properties. Designing these active gels with tunable properties analogous to the cytoskeleton is a key prerequisite for creating biomimetic systems to study cellular behavior such as division and motility. Active gels form ephemeral networks with long-range but temporary active mechanical contacts. In this talk, I will describe how microscopic dynamics modify the macroscopic mechanical properties of extensile microtubule networks. Rheological measurements reveal a non-monotonic dependence on the applied shear rate. A simple phenomenological model, which describes the network as a collection of fluid-like and solid-like elements, quantitatively explains the shear-rate-dependent viscosity in terms of locally-measured activity-induced flows. Fast, active elements remodel the network and therefore do not transmit elastic stresses, while slow, temporarily crosslinked elements behave elastically until they break and reform under shear.