Dual antagonistic role of motor proteins in fluidizing active networks

Crosslinking and depletion determine spatial instabilities in cytoskeletal active matter

“…In the concluding stages of our work, we became aware of a complementary, independent effort by the group of Guillaume Duclos who studied instabilities in kinesinmicrotubule active fluids. 37…”

Self-mixing in microtubule-kinesin active fluid from nonuniform to uniform distributions of activities

“…Overall, this work demonstrated that the mixing of nonuniform active fluid systems is fundamentally different from mixing in uniform active fluids. Our findings show that active fluid mixing involves complex interplays among ATP dispersion at the front of the active-inactive interface (which can be either diffusionlike or superdiffusion-like), active transport of ATP behind the front (which is constantly superdiffusionlike), and possibly a fluid-gel transition of the microtubule network, 50 as well as the spatial distribution of activity. This work paves the path to the design of microfluidic devices that use active fluid to internally promote or optimize the micromixing process 10 to enhance production efficiency in chemical and biological engineering and pharmaceutical development.…”

“…4) to convert ATP concentration profiles to mean speed profiles; however, this conversion would overestimate the mean speed profiles at low ATP concentrations, 49 because in low ATP concentration regimes motor dimers are immobile and act as passive crosslinkers in the microtubule network, causing the network to behave like an elastic gel, unlike in networks with high ATP concentrations where motors are mobile and thus the network is fluid. 48,50 Michaelis-Menten kinetics is an enzyme-based model that does not consider network rheology; thus, if the network rheology plays an important role, this conversion would overestimate the flow speed and thus overestimate . Despite these limitations, this simple model elucidated that the mixing in activeinactive fluid system at low flow-speed levels was governed by a diffusion-like process.…”

“…At the front of the active-inactive interface, ATP concentrations are low and thus the network can behave like an elastic gel because the inert kinesin motors act as crosslinkers between the microtubules. 50 Behind the front of the interface, where ATP concentrations are higher, the network behaves as a fluid-like network. (Fig.…”

“…49 The fluid-gel transition of the microtubule network was neglected to simplify the model, which may lead the model to overestimate the fluid speed at low ATP concentrations (see Discussion). 48,50 Using this ATP-activity equation (Eq. 4), we converted the ATP distribution to the mean speed distribution of active fluid (Fig.…”