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Abstract

The onset of self-organized droplet motion is studied in a poroelastic two-phase model with free boundaries and substrate friction. In the model, an active, gel-like phase and a passive, fluid-like phase interpenetrate on small length scales. A feedback loop between a chemical regulator, mechanical deformations, and induced fluid flow gives rise to oscillatory and irregular droplet motion accompanied by spatio-temporal contraction patterns inside the droplet. By numerical simulations in one spatial dimension, we cover extended parameter regimes of active tension and substrate friction, and reproduce experimentally observed oscillation periods and amplitudes. In line with recent experiments, the model predicts alternating forward and backward fluid flow at the boundaries with reversed flow in the center. Our model is a first step towards a more detailed model of moving microplasmodia of Physarum polycephalum.