Lastly, because the method derives cell cell forces indirectly through measurement of cell matrix traction forces, a fundamental assumption is that the measured traction forces fully capture all forces produced by the cells.
Sign-inverted traction forces (green vectors) are applied to the thin-plate model to generate an internal stress distribution of cells 1 and 2 that is consistent with the measured traction forces (red vectors).
In fact, our approach takes in-plane shear forces into account irrespectively of whether these forces are of elastic or viscous (dissipative) nature because the overall force balance with the substrate (and with the measured traction forces) must hold.
We review the development and application of two methods widely used to measure traction forces generated by cells on 2D substrates: (i) traction force microscopy with polyacrylamide hydrogels and (ii) calculation of traction forces with arrays of deformable microposts.
In the future, this technique will be used for measuring traction forces on complex patterns with multiple, spatially distinct ligands in systems for applying strain to the substrate, and in sandwich cultures that generate quasi-three-dimensional environments for cells.
Initial experiments measured the traction force exerted by adult fibroblasts relative to that exerted by fetal fibroblasts.
We used imaging and molecular probes to measure dynamics of F-actin polymerization, we used Cell Mapping Rheometry (CMR) [6] to measure cell traction force dynamics, and we used Optical Magnetic Twisting Cytometry (OMTC) [12] to measure cell stiffness dynamics.
Hence, measuring the traction force on a rigid substrate may lead to an decrease of resolving power in traction.
The internal cell-stress distributions were then calculated using the FEM such that the internal stresses were consistent with the measured cellular traction forces (see 'Finite element method for cell cell force measurements').
