Laboratoire Matière et Systèmes Complexes (MSC), UMR CNRS 7057 and Université Paris Diderot, Paris, France.
J Phys Condens Matter. 2010 May 19;22(19):194119. doi: 10.1088/0953-8984/22/19/194119. Epub 2010 Apr 26.
Whereas the adhesion and migration of individual cells have been well described in terms of physical forces, the mechanics of multicellular assemblies is still poorly understood. Here, we study the behavior of epithelial cells cultured on microfabricated substrates designed to measure cell-to-substrate interactions. These substrates are covered by a dense array of flexible micropillars whose deflection enables us to measure traction forces. They are obtained by lithography and soft replica molding. The pillar deflection is measured by video microscopy and images are analyzed with home-made multiple particle tracking software. First, we have characterized the temporal and spatial distributions of traction forces of cellular assemblies of various sizes. The mechanical force balance within epithelial cell sheets shows that the forces exerted by neighboring cells strongly depend on their relative position in the monolayer: the largest deformations are always localized at the edge of the islands of cells in the active areas of cell protrusions. The average traction stress rapidly decreases from its maximum value at the edge but remains much larger than the inherent noise due to the force resolution of our pillar tracking software, indicating an important mechanical activity inside epithelial cell islands. Moreover, these traction forces vary linearly with the rigidity of the substrate over about two decades, suggesting that cells exert a given amount of deformation rather than a force. Finally, we engineer micropatterned substrates supporting pillars with anisotropic stiffness. On such substrates cellular growth is aligned with respect to the stiffest direction in correlation with the magnitude of the applied traction forces.
虽然单个细胞的黏附和迁移在物理力方面已经得到了很好的描述，但多细胞聚集体的力学仍然知之甚少。在这里，我们研究了在微制造基板上培养的上皮细胞的行为，这些基板是为测量细胞与基板之间的相互作用而设计的。这些基板覆盖着密集排列的柔性微柱，微柱的挠度使我们能够测量牵引力。它们是通过光刻和软复制成型获得的。通过视频显微镜测量微柱的挠度，并使用自制的多粒子跟踪软件对图像进行分析。首先，我们对不同大小的细胞聚集体的牵引力的时空分布进行了特征描述。上皮细胞片层中的力学力平衡表明，相邻细胞施加的力强烈依赖于它们在单层中的相对位置：最大的变形总是集中在细胞岛的边缘，在细胞突起的活跃区域。平均牵引力迅速从边缘的最大值下降，但仍比我们的微柱跟踪软件的力分辨率引起的固有噪声大得多，这表明上皮细胞岛内部存在重要的机械活动。此外，这些牵引力与基质的刚度呈线性关系，跨度约为两个数量级，这表明细胞施加一定量的变形而不是力。最后，我们设计了具有各向异性刚度的微图案化基板，支撑具有各向异性刚度的微柱。在这样的基板上，细胞的生长与施加的牵引力的大小一致，与最硬的方向对齐。
