In cancer metastasis, embryonic development, and wound healing, cells can coordinate their motion, leading to collective motility. To characterize these cell-cell interactions, which include contact inhibition of locomotion (CIL), micropatterned substrates are often used to restrict cell migration to linear, quasi-one-dimensional paths. In these assays, collisions between polarized cells occur frequently with only a few possible outcomes, such as cells reversing direction, sticking to one another, or walking past one another. Using a computational phase field model of collective cell motility that includes the mechanics of cell shape and a minimal chemical model for CIL, we are able to reproduce all cases seen in two-cell collisions. A subtle balance between the internal cell polarization, CIL and cell-cell adhesion governs the collision outcome. We identify the parameters that control transitions between the different cases, including cell-cell adhesion, propulsion strength, and the rates of CIL. These parameters suggest hypotheses for why different cell types have different collision behavior and the effect of interventions that modulate collision outcomes. To reproduce the heterogeneity in cell-cell collision outcomes observed experimentally in neural crest cells, we must either carefully tune our parameters or assume that there is significant cell-to-cell variation in key parameters like cell-cell adhesion.

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. arXiv:1803.00337v3 [cond-mat.soft]

The onset of self-organized motion is studied in a poroelastic two-phase model with free boundaries for Physarum microplasmodia (MP). In the model, an active gel phase is assumed to be interpenetrated by a passive fluid phase on small length scales. A feedback loop between calcium kinetics, mechanical deformations, and induced fluid flow gives rise to pattern formation and the establishment of an axis of polarity. Altogether, we find that the calcium kinetics that breaks the conservation of the total calcium concentration in the model and a nonlinear friction between MP and substrate are both necessary ingredients to obtain an oscillatory movement with net motion of the MP. By numerical simulations in one spatial dimension, we find two different types of oscillations with net motion as well as modes with time-periodic or irregular switching of the axis of polarity. The more frequent type of net motion is characterized by mechano-chemical waves traveling from the front towards the rear. The second type is characterized by mechano-chemical waves that appear alternating from the front and the back. While both types exhibit oscillatory forward and backward movement with net motion in each cycle, the trajectory and gel flow pattern of the second type are also similar to recent experimental measurements of peristaltic MP motion. We found moving MPs in extended regions of experimentally accessible parameters, such as length, period and substrate friction strength. Simulations of the model show that the net speed increases with the length, provided that MPs are longer than a critical length of ≈ 120 μm. Both predictions are in line with recent experimental observations.

The onset of self-organized motion is studied in a poroelastic two-phase model with free boundaries for Physarum microplasmodia (MP). In the model, an active gel phase is assumed to be interpenetrated by a passive fluid phase on small length scales. A feedback loop between calcium kinetics, mechanical deformations, and induced fluid flow gives rise to pattern formation and the establishment of an axis of polarity. Altogether, we find that the calcium kinetics that breaks the conservation of the total calcium concentration in the model and a nonlinear friction between MP and substrate are both necessary ingredients to obtain an oscillatory movement with net motion of the MP. By numerical simulations in one spatial dimension, we find two different types of oscillations with net motion as well as modes with time-periodic or irregular switching of the axis of polarity. The more frequent type of net motion is characterized by mechano-chemical waves traveling from the front towards the rear. The second type is characterized by mechano-chemical waves that appear alternating from the front and the back. While both types exhibit oscillatory forward and backward movement with net motion in each cycle, the trajectory and gel flow pattern of the second type are also similar to recent experimental measurements of peristaltic MP motion. We found moving MPs in extended regions of experimentally accessible parameters, such as length, period and substrate friction strength. Simulations of the model show that the net speed increases with the length, provided that MPs are longer than a critical length of ≈ 120 µm. Both predictions are in line with recent experimental observations. 1 Introduction 1 Dynamic processes in biological systems such as cells are examples of when 2 spatio-temporal patterns develop far from thermodynamic equilibrium [1, 2]. One 3 fascinating instance of such active matter are intracellular molecular motors that 4 consume ATP [3] and can drive mechano-chemical contraction-expansion patterns [4] 5 and, ultimately, cell locomotion. Further biological examples of such phenomena are 6 discussed in [5-7]. 7 The true slime mold Physarum polycephalum is a well known model organism [8] 8 that exhibits mechano-chemical spatio-temporal patterns. Previous research in 9 Physarum has addressed many different topics in biophysics, such as genetic activity [9], 10 habituation [10], decision making [11] and cell locomotion [12, 13]. Physarum is an 11 May 6, 2019 1/20 unicellular organism, which builds large networks that exhibit self-organized 12 synchronized contraction patterns [8, 14, 15]. These contractions enable shuttle 13 streaming in the tubular veins of the network and allow for efficient nutrient transport 14 throughout the organism [16]. Many groups have investigated the network's 15 dynamics [17-19], however size and complex topology of these networks make analyzing 16 and modeling them challenging. 17 Physarum microplasmodia (MP) allow one to study Physarum's internal dynamics 18 in a simpler setup. These MPs ca...

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