The collective behavior of biological systems is today an intriguing open challenge in several aspects. Biological systems differ from non-living, passive systems because of the continuous injection and dissipation of energy at the single-cell level. This particular feature enables fascinating emergent behavior with important biological functions. For instance, epithelial tissues are made by densely packed cells whose size oscillations synchronize in time and propagate forming wave patterns, which are able to propagate stress forces more efficiently. These mechanisms are crucial in key biological functions such as dorsal closure in embryogenesis and wound healing. Similarly, cardiac cells contracts and expand at every heartbeat following the propagation of an electric pulse originated in the heart: physiological activity corresponds to a regular wave propagation, whereas the emergence of heterogeneities gives rise to irregular waves leading to tachycardia and ventricular fibrillation. A microscopic, physically-based understanding of such collective behavior represents an outstanding challenge and has potential strong impact in the treatment of such disorders.
NewGenActive propose a new generation of active matter models to elucidate the emergence of the collective behavior above-mentioned. Active matter is a fertile research framework, developed in the last three decades to describe the collective behavior of active motile systems, i.e. collectives whose units can individually sustain a self-propelled motion in absence of external mechanical forces. Typical examples of such systems are bacteria, fishes, birds, or pedestrian. Because of its intrinsic non-equilibrium nature, active behavior is not constrained by equilibrium laws. As a direct consequence, non-equilibrium phases such as flocking (when a group of birds fly in the same direction) or motility-induced phase separation (when repulsive particles cluster together) emerge experimentally and have been theoretically explained.
The physics of dense tissues such as cardiac and epithelial tissues presents different challenges. In these cases, the position of the particles is almost fixed in time, while their shape and size change because of activity. The main objective of NewGenActive is then understanding how active shape changes affect the collective dynamics of dense systems. To do so, we introduce a new generation of active matter models whose active ingredient is the capability to change the cell's size or shape, rather then introducing a self-propulsion as in motile active matter. The project aims at understanding the emergence of collective behavior depending on the microscopic interactions between the cells.
The project therefore pursues the definition of a new class of active models with the following objectives:
1) unveil the minimal ingredients to observe the emergence of size waves in a system of actively deformable particles;
2) exploit the model introduced to understand the effect of anisotropy on the dynamics (i.e. non-circular cells);
3) investigate the effect of an energy potential associated to internal degrees of freedom regulating the sizes and the emergence of liquid-liquid phase separation;
4) formulate a thermodynamically consistent framework to investigate the energy fluxes in deformable active particles.
