Figure 2
Systematic tests illustrate substantial ambiguity in the choice of regularization parameters. (a) Schematic of the employed procedure to test the reconstruction methods. (a,i) Artificial traction pattern consisting of circular spots that uniformly exert a traction of 100 Pa. (a,ii) Analytical calculation of the gel displacements. (a,iii) The displacement field is sampled at random positions representing measurements of motion of fiducial markers. (a,iv) Reconstruction of the traction. (b) Central formula summarizing different regularization approaches. (c) Dependence of various error measures on the regularization parameters. (b,i)–(b,v) Error measures defined in Eqns. (9–12) exhibit various extrema and turning points, making the definition of an optimal parameter challenging. Note that the minima of the errors do not correspond to values of regularization parameters suggested by the L-curve criterion (Green dotted lines vs. black dotted lines). DTMA: Deviation of traction magnitude at adhesion, DTMB: deviation of traction magnitude in background. (b,I)–(b,V) Traction fields calculated with regularization parameters that correspond to the error minima at the black dotted lines. Space bar: 5 μm.
