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Traction Force Microscopy Fluorescent red polystyrene microspheres (500 nm diameter, Molecular Probes) were mixed with the alginate solution at a mass ratio of 0.0008:1 before mixing with the CaSO₄ slurry to form gels.

Cells were plated at a density of 6,000 cells per cm², and after 24 h, images of cells and the microbeads under the cells were captured by using a fluorescence microscope (Nikon). The cells were then exposed to 10 m g/ml Nocodazole. After 5 min, the images of the cells and microbeads were captured again. The cells were subsequently removed from the gel by exposure to a 5% SDS solution. After visually confirming the removal of cells, the locations of the relaxed microbeads were imaged again. The relative bead displacements before and after exposure of cells to Nocodazole were analyzed to quantify the stress applied by the cells, as described (1).

1. Wang, N., Marija, T., Chen, J., Mijalovich, S. M., Butler, J. P., Fredberg, J. J. & Stamenovic, D. (2002) Am. J. Physiol. 282, C606-C616.

Fig. 6. Changes in the Nocodazole-induced cellular traction forces were quantified by using traction force microscopy. Traction field maps before (a) and after (b) exposing cells to the Nocodazole demonstrate the traction force exerted by the cells on the gels increases (˜22%) with treatment. The arrows indicate the displacement of beads underlying the cells and associated traction stress. The color indicates the magnitudes of traction force, with red indicating the highest stress. Cells were cultured on the softest gels (E ~ 20 kPa) in these experiments.