Fig. 4. Impact of Poisson’s ratio on the experimentally acquired data from a HeLa cell.

a Total internal reflection fluorescence structured illumination microscopy (TIRF-SIM) image of a HeLa cell adhering to the elastic substrate. Scale = 5 μm (reproduced and reanalysed data from Li et al.⁶¹). b Magnitude of axial and lateral displacements during HeLa cell adhesion were estimated by employing astigmatic traction force microscopy (aTFM). c Magnitude of the reconstructed normal and shear stresses considering both axial and lateral components of the displacement when the Poisson’s ratio of the substrate ranges between 0-0.5. d Magnitude of the reconstructed normal and shear stresses when the axial component of displacements was ignored and only the lateral components were considered. e Contour map of the error for a hypothetical problem (for HeLa cell adhesion) considering all combinations of the possible true Poisson’s ratio and the Poisson’s ratio used in TFM analysis, varying from 0 to 0.5.