Hecht Fabian M, Rheinlaender Johannes, Schierbaum Nicolas, Goldmann Wolfgang H, Fabry Ben, Schäffer Tilman E
Institute of Applied Physics, University of Tübingen, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
Department of Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052 Erlangen, Germany.
Soft Matter. 2015 Jun 21;11(23):4584-4591. doi: 10.1039/c4sm02718c.
We developed force clamp force mapping (FCFM), an atomic force microscopy (AFM) technique for measuring the viscoelastic creep behavior of live cells with sub-micrometer spatial resolution. FCFM combines force-distance curves with an added force clamp phase during tip-sample contact. From the creep behavior measured during the force clamp phase, quantitative viscoelastic sample properties are extracted. We validate FCFM on soft polyacrylamide gels. We find that the creep behavior of living cells conforms to a power-law material model. By recording short (50-60 ms) force clamp measurements in rapid succession, we generate, for the first time, two-dimensional maps of power-law exponent and modulus scaling parameter. Although these maps reveal large spatial variations of both parameters across the cell surface, we obtain robust mean values from the several hundreds of measurements performed on each cell. Measurements on mouse embryonic fibroblasts show that the mean power-law exponents and the mean modulus scaling parameters differ greatly among individual cells, but both parameters are highly correlated: stiffer cells consistently show a smaller power-law exponent. This correlation allows us to distinguish between wild-type cells and cells that lack vinculin, a dominant protein of the focal adhesion complex, even though the mean values of viscoelastic properties between wildtype and knockout cells did not differ significantly. Therefore, FCFM spatially resolves viscoelastic sample properties and can uncover subtle mechanical signatures of proteins in living cells.
我们开发了力钳力映射（FCFM）技术，这是一种原子力显微镜（AFM）技术，用于以亚微米空间分辨率测量活细胞的粘弹性蠕变行为。FCFM将力-距离曲线与尖端-样品接触期间添加的力钳阶段相结合。从力钳阶段测量的蠕变行为中，提取定量的粘弹性样品特性。我们在软聚丙烯酰胺凝胶上验证了FCFM。我们发现活细胞的蠕变行为符合幂律材料模型。通过连续快速记录短时间（50-60毫秒）的力钳测量，我们首次生成了幂律指数和模量缩放参数的二维图。尽管这些图揭示了这两个参数在整个细胞表面的巨大空间变化，但我们从对每个细胞进行的数百次测量中获得了可靠的平均值。对小鼠胚胎成纤维细胞的测量表明，单个细胞之间的平均幂律指数和平均模量缩放参数差异很大，但这两个参数高度相关：更硬的细胞始终显示出较小的幂律指数。这种相关性使我们能够区分野生型细胞和缺乏纽蛋白（一种粘着斑复合物的主要蛋白质）的细胞，尽管野生型细胞和基因敲除细胞之间的粘弹性特性平均值没有显著差异。因此，FCFM在空间上解析了粘弹性样品特性，并可以揭示活细胞中蛋白质的微妙机械特征。
