Traction force reconstruction assessment on real three-dimensional matrices and cellular morphologies

Traction force microscopy (TFM) allows to estimate tractions on the surface of cells when they mechanically interact with hydrogel substrates that mimic the extracellular matrix (ECM). The field of mechanobiology has a strong interest in using TFM in 3D in vitro models. However, there are a number of challenges that hamper the accuracy of 3D TFM and that are often bypassed. In this study, the computational efficiency and accuracy of TFM, referred to traction reconstruction from synthetically generated (control) ground truth solutions, are assessed from four different perspectives: magnitude of cellular pulling force (and hence strain level achieved in the hydrogel), effect of the complexity of the cellular morphology, accuracy and computational efficiency of forward vs inverse traction recovery methods, and the effect of incorrectly selecting a constitutive model that describes the behavior of the ECM (i.e. linear/nonlinear). The main results showed: (i) traction reconstruction is more challenging for complex cell morphologies, (ii) there is no significant impact of the magnitude of cellular pulling force on the overall reconstruction accuracy, and (iii) modeling a nonlinear hydrogel with a linear constitutive model leads to non-negligible errors (up to 80% and 30% for forward and inverse methodologies, respectively) in traction reconstruction. This study expands the characterization of the accuracy and efficiency of 3D TFM, highlighting important factors to be considered in future 3D TFM in vitro applications.