Figure 6:

Experiments depicting stiffness sensing and response by MDA-MB-231 cells. (a) Representative elongated morphology of a cell in a control matrix of collagen, with no embedded PNIPAAm microspheres at 37°C. (b) Representative rounded morphology of a cell in a PNIPAAm-embedded collagen matrix, when the embedded PNIPAAm microspheres contracted at 37°C. (c) For many independent cells in control and PNIPAAm-matrices, the length of the longest axis (feret’s diameter) was measured. In the contracted PNIPAAm-matrices, the cells had significantly smaller feret’s diameter (p = 8 × 10⁻²¹, rank sum). (d) For many independent cells in control and PNIPAAm-matrices, the ratio of the square of the cell perimeter (P) to the cell area (A) was computed. In the contracted PNIPAAm-matrices, P²/A was significantly smaller (p = 4 × 10⁻¹⁹, rank sum). (e) A representative image of a cell in a control matrix of collagen, with no embedded PNIPAAm microspheres at 37°C. (f) Cell-induced displacement (|U|) of the matrix shown in panel e. (g) A representative image of a cell in a PNIPAAm-embedded matrix of collagen at 37°C. (h) Cell-induced displacement (|U|) of the matrix shown in panel g. (i) The 80th percentile of the magnitude of displacement |U| inside the dumbell-shaped regions (specified regions in panels e–h) were plotted for cells on control and contracted matrices. PNIPAAm-embedded matrices had significantly less deformation (p = 0.0076, rank sum), meaning that cellular activities (cell generated forces) were drastically reduced due to the softening of the contracted PNIPAAm-matrices. In panels c, d, and i, dots represent independent cells; lines indicate medians.