Agosti A, Ambrosi D, Turzi S
Dipartimento di Matematica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy.
DISMA, Politecnico di Torino, corso Duca degli Abruzzi 24, 10129 Torino, Italy.
Phys Rev E. 2018 May;97(5-1):052410. doi: 10.1103/PhysRevE.97.052410.
When living cells are observed at rest on a flat substrate, they can typically exhibit a rounded (symmetric) or an elongated (polarized) shape. Although the cells are apparently at rest, the active stress generated by the molecular motors continuously stretches and drifts the actin network, the cytoskeleton of the cell. In this paper we theoretically compare the energy stored and dissipated in this active system in two geometric configurations of interest: symmetric and polarized. We find that the stored energy is larger for a radially symmetric cell at low activation regime, while the polar configuration has larger strain energy when the active stress is beyond a critical threshold. Conversely, the dissipation of energy in a symmetric cell is always larger than that of a nonsymmetric one. By a combination of symmetry arguments and competition between surface and bulk stress, we argue that radial symmetry is an energetically expensive metastable state that provides access to an infinite number of lower-energy states, the polarized configurations.
当在平坦基质上观察静止的活细胞时，它们通常会呈现圆形（对称）或细长形（极化）。尽管细胞看似静止，但分子马达产生的主动应力会持续拉伸并使肌动蛋白网络（细胞的细胞骨架）发生漂移。在本文中，我们从理论上比较了在两种感兴趣的几何构型（对称和极化）下，该主动系统中存储和耗散的能量。我们发现，在低激活状态下，径向对称细胞存储的能量更大，而当主动应力超过临界阈值时，极化构型具有更大的应变能。相反，对称细胞中的能量耗散总是大于非对称细胞。通过对称性论证以及表面应力和体应力之间的竞争，我们认为径向对称是一种能量消耗大的亚稳态，它可通向无数能量更低的状态，即极化构型。
