Department of Mechanical Engineering, Tufts University, Medford, Massachusetts, USA.
Biophys J. 2013 May 21;104(10):2123-31. doi: 10.1016/j.bpj.2013.04.019.
When measuring the elastic (Young's) modulus of cells using AFM, good attachment of cells to a substrate is paramount. However, many cells cannot be firmly attached to many substrates. A loosely attached cell is more compliant under indenting. It may result in artificially low elastic modulus when analyzed with the elasticity models assuming firm attachment. Here we suggest an AFM-based method/model that can be applied to extract the correct Young's modulus of cells loosely attached to a substrate. The method is verified by using primary breast epithelial cancer cells (MCF-7) at passage 4. At this passage, approximately one-half of cells develop enough adhesion with the substrate to be firmly attached to the substrate. These cells look well spread. The other one-half of cells do not develop sufficient adhesion, and are loosely attached to the substrate. These cells look spherical. When processing the AFM indentation data, a straightforward use of the Hertz model results in a substantial difference of the Young's modulus between these two types of cells. If we use the model presented here, we see no statistical difference between the values of the Young's modulus of both poorly attached (round) and firmly attached (close to flat) cells. In addition, the presented model allows obtaining parameters of the brush surrounding the cells. The cellular brush observed is also statistically identical for both types of cells. The method described here can be applied to study mechanics of many other types of cells loosely attached to substrates, e.g., blood cells, some stem cells, cancerous cells, etc.
当使用原子力显微镜（AFM）测量细胞的弹性（杨氏）模量时，细胞与基底的良好附着至关重要。然而，许多细胞无法牢固地附着在许多基底上。在压痕过程中，附着不牢固的细胞的顺应性更大。当使用假设牢固附着的弹性模型进行分析时，可能会导致杨氏模量人为降低。在这里，我们提出了一种基于 AFM 的方法/模型，可用于提取附着不牢固的细胞的正确杨氏模量。该方法通过使用第 4 代原代乳腺上皮癌细胞（MCF-7）进行了验证。在这个传代中，大约有一半的细胞与基底形成足够的附着力，从而能够牢固地附着在基底上。这些细胞看起来铺展良好。另一半细胞没有形成足够的附着力，而是附着在基底上。这些细胞看起来呈球形。在处理 AFM 压痕数据时，如果直接使用赫兹模型，这两种类型的细胞的杨氏模量之间会存在显著差异。如果使用我们提出的模型，我们会发现附着不牢（圆形）和附着牢固（接近平坦）的细胞之间杨氏模量没有统计学差异。此外，所提出的模型允许获得围绕细胞的刷子的参数。观察到的细胞刷对于两种类型的细胞也是统计学上相同的。这里描述的方法可以应用于研究许多其他类型的附着不牢的细胞的力学特性，例如血细胞、一些干细胞、癌细胞等。
