Fig. 2.

Collagen matrix deformations due to contractile forces. An MDA-MD-231 breast carcinoma cell was allowed to invade into a collagen gel for two days and had reached a depth of approximately 200 µm below the gel surface. The left image shows the structure of the collagen matrix surrounding the cell, recorded with a modulation contrast imaging mode (in addition, the contrast was digitally enhanced to better visualize the collagen matrix). The cell was then treated with an over-dose of 250 µM ML-7 (a myosin light chain kinase inhibitor) to release cytoskeletal tension stored in the actin cytoskeleton and to detach the cell from the matrix. Within less than 2 minutes, the collagen matrix returned to its undeformed, relaxed state, and a second image was recorded (middle). The matrix deformations (right) were computed using a difference-with-interpolation method from the left (contracted) and the middle (relaxed) image (Raupach et al., 2007).