The cytoskeleton gives a cell its main structure and rigidity. It plays a significant role during many (force sensitive) mechanical cues from outside the cell. The anisotropy of the cytoskeleton...Show moreThe cytoskeleton gives a cell its main structure and rigidity. It plays a significant role during many (force sensitive) mechanical cues from outside the cell. The anisotropy of the cytoskeleton has been shown to control the geometry and forces of adherent cells. Bases on the the shape of curved cell edge segments of single cells, the size of internal stresses and traction forces can be calculated. However, such methods have not yet been applied to clusters of cells. Here we introduce two methods to describe the mechanical equilibrium of cell doublets. Either in a discontinuous way, where both cells are treated separately, or continuous, where we do not differentiate between the cells and treat it as a single cell.Show less
Micropillar arrays are used to measure traction forces of individual cells and of cells in tissue. For this technique single cells are placed on poly-di-methyl siloxane (PDMS) micropillar arrays...Show moreMicropillar arrays are used to measure traction forces of individual cells and of cells in tissue. For this technique single cells are placed on poly-di-methyl siloxane (PDMS) micropillar arrays and observed on an inverted high-resolution optical microscope. As of the requirements for a high-resolution inverted microscopy, the images of the micropillar array are taken through the cell.A refractive index change between the cell and cell medium results in refraction of light at their interface. Here we introduce a method to characterize astigmatism caused by this varying refractive index. We found that that astigmatism can lead to aberrations up to 400 nm. Further, based on the same method we were able to estimate the refractive index of the nucleus to be $1.366\pm0.004$. Our results demonstrate that astigmatism should be taken into account during traction force measurements, especially when measuring forces close to the nucleus.Show less
