在胚胎形态发生期间,组织经历剧烈的变形以形成功能性器官。同样,在成年动物中,活细胞和组织不断受到力和变形。因此,胚胎发育的成功和生理功能的适当维持依赖于细胞承受机械应力的能力以及它们以集体方式流动的能力。在这些事件中,机械扰动可以源自单细胞水平的活动过程,与周围组织和器官施加的外部应力竞争。然而,对组织力学的研究在某种程度上仅限于对外力或内在力的反应。在这项工作中,我们使用2D融合组织的活动顶点模型来研究外部变形的相互作用,这些外部变形全局施加到组织上,内部主动应力由于细胞运动性而在细胞水平上局部出现。我们阐明,特别是,全局外部和局部内部主动驱动之间的这种相互作用的方式决定了整个组织的新兴机械性能。对于固液堵塞或未堵塞过渡附近的组织,我们发现了许多令人着迷的流变现象,包括屈服,剪切稀化,连续剪切增稠,和不连续的剪切增稠。这些模型预测为理解最近观察到的体内非线性流变行为提供了框架。
During embryonic morphogenesis, tissues undergo dramatic deformations in order to form functional organs. Similarly, in adult animals, living cells and tissues are continually subjected to forces and deformations. Therefore, the success of embryonic development and the proper maintenance of physiological functions rely on the ability of cells to withstand mechanical stresses as well as their ability to flow in a collective manner. During these events, mechanical perturbations can originate from active processes at the single-cell level, competing with external stresses exerted by surrounding tissues and organs. However, the study of tissue mechanics has been somewhat limited to either the response to external forces or to intrinsic ones. In this work, we use an active vertex model of a 2D confluent tissue to study the interplay of external deformations that are applied globally to a tissue with internal active stresses that arise locally at the cellular level due to cell motility. We elucidate, in particular, the way in which this interplay between globally external and locally internal active driving determines the emergent mechanical properties of the tissue as a whole. For a tissue in the vicinity of a solid-fluid jamming or unjamming transition, we uncover a host of fascinating rheological phenomena, including yielding, shear thinning, continuous shear thickening, and discontinuous shear thickening. These model predictions provide a framework for understanding the recently observed nonlinear rheological behaviors in vivo.