Simulations of complex particle transport in heterogeneous active liquids

Thermal-fluctuation and external force-induced motion of particles provide mechanical and rheological information for viscoelastic liquids and soft solids. Although particle tracking is well-developed, analysis of particle trajectories in active heterogeneous materials, such as living cells, is usually not simple or straightforward. These trajectories are sometimes composed of several concurrent processes occurring simultaneously or episodically in a complex fluid. Here, we introduce simulations that generate 2-dimensional trajectories of probe transport in a viscous liquid as a tool for complex-trajectory analysis. These computer simulations illustrate cases that are physically relevant and highlight key features, such as spatial confinements or convective speeds, which can for example define a cell's internal structure and active transport along tubules or fibers. Comparison to experimental data will allow quantitative identification of various concurrent processes and understanding of their time dependence. We examine several well-defined cases of particle motion that occur in soft samples, including living cells, and present information from the analysis as well as new approaches for complex processes.