Figure 1.

Theoretical characterization of STFM. (a) Schematic representation of a typical TFM setup. An elastic polyacrylamide gel filled with fluorescent marker beads is covalently attached to a glass coverslip and functionalized with proteins that facilitate cell adherence. Traction forces applied by the cell to the top surface of the gel results in lateral displacements of the gel which can be quantified by imaging the displacement of the beads within the gel. (b) Theoretical relationship between the sampling density and the Nyquist limit (dashed line), with three different bead densities highlighted (red, blue, green as labeled), exemplifying that a bead density of 15 μm^–2 would allow the recovery of tractions 500 nm in size. Crosses show the smallest recoverable tractions from simulations performed at the three bead densities shown in Figure 2. Open circles show the smallest recoverable traction from simulations where noise is added and regularization used.