Ferreira João P S, Kuang Mei, Marques Marco, Parente Marco P L, Damaser Margot S, Natal Jorge Renato M
Mechanical Engineering Department, Faculty of Engineering, Porto, Portugal.
Institute of Science and Innovation in Mechanical and Industrial Engineering (INEGI), Porto, Portugal.
Biomech Model Mechanobiol. 2020 Dec;19(6):2061-2079. doi: 10.1007/s10237-020-01324-5. Epub 2020 Apr 30.
A mechanical model is presented to analyze the mechanics and dynamics of the cell cortex during indentation. We investigate the impact of active contraction on the cross-linked actin network for different probe sizes and indentation rates. The essential molecular mechanisms of filament stretching, cross-linking and motor activity, are represented by an active and viscous mechanical continuum. The filaments behave as worm-like chains linked either by passive rigid linkers or by myosin motors. In the first example, the effects of probe size and loading rate are evaluated using the model for an idealized rounded cell shape in which properties are based on the results of parallel-plate rheometry available in the literature. Extreme cases of probe size and indentation rate are taken into account. Afterward, AFM experiments were done by engaging smooth muscle cells with both sharp and spherical probes. By inverse analysis with finite element software, our simulations mimicking the experimental conditions show the model is capable of fitting the AFM data. The results provide spatiotemporal dependence on the size and rate of the mechanical stimuli. The model captures the general features of the cell response. It characterizes the actomyosin cortex as an active solid at short timescales and as a fluid at longer timescales by showing (1) higher levels of contraction in the zones of high curvature; (2) larger indentation forces as the probe size increases; and (3) increase in the apparent modulus with the indentation depth but no dependence on the rate of the mechanical stimuli. The methodology presented in this work can be used to address and predict microstructural dependence on the force generation of living cells, which can contribute to understanding the broad spectrum of results in cell experiments.
本文提出了一个力学模型，用于分析压痕过程中细胞皮层的力学和动力学。我们研究了不同探针尺寸和压痕速率下，主动收缩对交联肌动蛋白网络的影响。细丝拉伸、交联和马达活性的基本分子机制，由一个主动且粘性的力学连续体表示。细丝表现为通过被动刚性连接体或肌球蛋白马达连接的类蠕虫链。在第一个例子中，使用该模型对理想化的圆形细胞形状评估探针尺寸和加载速率的影响，其中细胞属性基于文献中平行板流变学的结果。考虑了探针尺寸和压痕速率的极端情况。之后，通过使用尖锐和球形探针接触平滑肌细胞进行了原子力显微镜（AFM）实验。通过使用有限元软件进行反分析，我们模拟实验条件的结果表明该模型能够拟合AFM数据。结果提供了对机械刺激的大小和速率的时空依赖性。该模型捕捉了细胞反应的一般特征。它通过显示（1）高曲率区域收缩水平更高；（2）随着探针尺寸增加压痕力更大；以及（3）表观模量随压痕深度增加但与机械刺激速率无关，将肌动球蛋白皮层在短时间尺度上表征为活性固体，在长时间尺度上表征为流体。本文提出的方法可用于解决和预测微观结构对活细胞力产生的依赖性，这有助于理解细胞实验中的广泛结果。
