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Abstract：
Cell mechanics are a biophysical indicator of cell state, such as cancer metastasis, leukocyte activation, and cell cycle progression. Atomic force microscopy (AFM) is a widely used technique to measure cell mechanics, where the Young modulus of a cell is usually derived from the Hertz contact model. However, the Hertz model assumes that the cell is an elastic, isotropic, and homogeneous material and that the indentation is small compared to the cell size. These assumptions neglect the effects of the cytoskeleton, cell size and shape, and cell environment on cell deformation. In this study, we investigated the influence of cell size on the estimated Young\'s modulus using liposomes as cell models. Liposomes were prepared with different sizes and filled with phosphate buffered saline (PBS) or hyaluronic acid (HA) to mimic the cytoplasm. AFM was used to obtain the force indentation curves and fit them to the Hertz model. We found that the larger the liposome, the lower the estimated Young\'s modulus for both PBS-filled and HA-filled liposomes. This suggests that the Young modulus obtained from the Hertz model is not only a property of the cell material but also depends on the cell dimensions. Therefore, when comparing or interpreting cell mechanics using the Hertz model, it is essential to account for cell size.
摘要：
细胞力学是细胞状态的生物物理指标，比如癌症转移，白细胞活化，和细胞周期进程。原子力显微镜（AFM）是一种广泛用于测量细胞力学的技术，其中细胞的杨氏模量通常来自赫兹接触模型。然而,赫兹模型假设细胞是弹性的，各向同性，和均质材料，并且与单元尺寸相比，压痕较小。这些假设忽略了细胞骨架的影响，细胞大小和形状，和细胞环境对细胞变形的影响。在这项研究中,我们使用脂质体作为细胞模型研究了细胞大小对估计杨氏模量的影响。制备具有不同尺寸的脂质体,并用磷酸盐缓冲盐水(PBS)或透明质酸(HA)填充以模拟细胞质。使用AFM获得力压痕曲线并将其拟合到赫兹模型。我们发现脂质体越大，PBS填充脂质体和HA填充脂质体的估计杨氏模量越低。这表明从赫兹模型获得的杨氏模量不仅是单元材料的属性，而且取决于单元尺寸。因此,当使用赫兹模型比较或解释细胞力学时，重要的是要考虑细胞的大小。
