Overby Darryl R, Matthews Benjamin D, Alsberg Eben, Ingber Donald E
Vascular Biology Program, Departments of Pathology and Surgery, Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Acta Biomater. 2005 May;1(3):295-303. doi: 10.1016/j.actbio.2005.02.003. Epub 2005 Mar 31.
The rheology of cells and sub-cellular structures, such as focal adhesions, are important for cell form and function. Here we describe electromagnetic pulling cytometry (EPC), a technique to analyze cell rheology by applying dynamic tensional forces to ligand-coated magnetic microbeads bound to cell surface integrin receptors. EPC utilizes an electromagnetic microneedle that is integrated with a computerized control and image acquisition system and an inverted microscope and CCD camera to monitor bead displacement. Arbitrary force regimens may be defined over a wide range of frequency (DC to 10 Hz) and force (100 pN to 10 nN). With EPC, the viscoelastic creep response of individual focal adhesions was measured over three decades in time using RGD-coated magnetic microbeads bound to integrins that induce local focal adhesion assembly and coupling to the internal cytoskeleton. These data were compared to the power-law-like predictions from the soft glassy model of cell rheology proposed by Fabry et al. Although power-law-like behavior was observed in some focal adhesions, 52% of these structures did not exhibit power-law-like behavior, but instead exhibited either a multi-phase response characterized by abrupt changes in slope or experienced a retraction in the opposite direction to the applied force, especially in response to prolonged force application. These data suggest that while the soft glassy model may provide reasonable estimates for aggregate mechanical behavior of living cells, the rheological behavior of individual focal adhesions may be more heterogeneous and complex than suggested by the soft glassy model. These results are considered in context with the hierarchical nature of cytoskeletal architecture.
细胞及亚细胞结构（如粘着斑）的流变学对于细胞形态和功能很重要。在此，我们描述了电磁牵引细胞术（EPC），这是一种通过对与细胞表面整合素受体结合的配体包被磁性微珠施加动态张力来分析细胞流变学的技术。EPC利用与计算机控制和图像采集系统集成的电磁微针以及倒置显微镜和电荷耦合器件相机来监测微珠位移。可以在很宽的频率范围（直流到10赫兹）和力范围（100皮牛到10纳牛）内定义任意的力方案。利用EPC，使用与诱导局部粘着斑组装并与内部细胞骨架耦合的整合素结合的RGD包被磁性微珠，在三个数量级的时间内测量了单个粘着斑的粘弹性蠕变响应。将这些数据与法布里等人提出的细胞流变学软玻璃态模型的幂律样预测进行了比较。尽管在一些粘着斑中观察到了幂律样行为，但这些结构中有52%没有表现出幂律样行为，而是表现出以斜率突然变化为特征的多相响应，或者经历了与施加力相反方向的回缩，尤其是在长时间施加力时。这些数据表明，虽然软玻璃态模型可能为活细胞的总体力学行为提供合理估计，但单个粘着斑的流变行为可能比软玻璃态模型所表明的更加异质和复杂。结合细胞骨架结构的层次性质来考虑这些结果。
