To perform digital image correlation, or DIC, using the DIC software, import the images derived from the sheer assay recording to the DIC software, preferably in the TIF file format. For an optimized correlation, select the sum of differential option which tracks the deformation of a new image with respect to the last image. Select a subset size of 31 by 31 pixels with a step size of 20 pixels.
Map out the region of interest for a chosen single cell. For an irregular shape, such as a cell, use a polygon mask to map out the cell's geometry. Select arbitrary points within the mapped cell to track deformation.
After mapping, choose specific points on the cell, like the nucleus or cytoplasm, to be analyzed by clicking Add a Strain Gauge and drawing out individual strain gauges at points within the defined cellular boundary. Click on Start to begin the strain processing and obtain strain versus time data. The strain time plot generated as a result of this correlation can be exported as a CSV file for further analysis in MATLAB.
Double click or right click on the generated strain time plot and select Export Data. DIC of image frames extracted from sheer assay recordings successfully produced strain time data compatible with the creep stress response. The results of studies using the sheer assay technique showed that cancer cells were generally more mechanically compliant and less viscous than normal cells.
The stiffness and viscosities of the cells were observed to decrease with increased cancer progression from a normal cell state to a slightly metastatic state and finally to a highly metastatic state. However, the relaxation time for these cell types showed no significant variations.
