Artificial cytoplasmic streaming*

Recent experiments in cell biology have probed the impact of artificially-induced intracellular flows and transport in cell division. Using focused light localised in a small region of the cell, a global thermo-viscous flow was induced inside the cell in these studies; this is known as focused-light-induced cytoplasmic streaming (FLUCS). Here we present an analytical, theoretical model of FLUCS. The focused light induces a small, local temperature change, causing a small change in the density and viscosity of the fluid locally. This heat spot translates along a finite scan path. We show that the leading-order instantaneous flow results from thermal expansion and depends linearly on the heat-spot amplitude. The net displacement of a passive tracer after a full scan period is quadratic in the heat-spot amplitude and is due to both thermal expansion and thermal viscosity changes. The far-field average velocity of tracers is a source dipole, showing excellent agreement with recent experimental data. Our quantitative model will enable future work on artificial cytoplasmic streaming.