Mixing and stretching in microfluidics with active matter

Microtubules and motor proteins have attracted great scientific interests in the past two decades for their rich non-equilibrium dynamics and importance in cell division. In this talk, we propose an application using microtubules and light-activatable motors to design flow fields in microfluidic devices. Motor proteins can bind and walk on microtubules and generate active stresses. Active fluids with such living matter can be chaotic without a control mechanism, limiting their utility for bioengineering applications. Here we use the recently-developed light-activatable motors, which only crosslink the microtubules under illumination, to control the fluid flows through the spatiotemporal design of light patterns. In particular, we present how to generate local extensional and rotational flows in this system, with no requirements on the geometry of channels or control of inlet and outlet flows. A continuum model for both the active microtubules and emergent flows has been formulated and shown good agreement with experiments. In the end, we present the experiments where different types of flows are generated simultaneously at different locations in a single channel. Our results may be used for developing programmable lab-on-a-chip devices in the future.