title: Two-Layer Elastographic 3-D Traction Force Microscopy.
abstract: Cellular traction force microscopy (TFM) requires knowledge of the mechanical properties of the substratum where the cells adhere to calculate cell-generated forces from measurements of substratum deformation. Polymer-based hydrogels are broadly used for TFM due to their linearly elastic behavior in the range of measured deformations. However, the calculated stresses, particularly their spatial patterns, can be highly sensitive to the substratum's Poisson's ratio. We present two-layer elastographic TFM (2LETFM), a method that allows for simultaneously measuring the Poisson's ratio of the substratum while also determining the cell-generated forces. The new method exploits the analytical solution of the elastostatic equation and deformation measurements from two layers of the substratum. We perform an in silico analysis of 2LETFM concluding that this technique is robust with respect to TFM experimental parameters, and remains accurate even for noisy measurement data. We also provide experimental proof of principle of 2LETFM by simultaneously measuring the stresses exerted by migrating Physarum amoeboae on the surface of polyacrylamide substrata, and the Poisson's ratio of the substrata. The 2LETFM method could be generalized to concurrently determine the mechanical properties and cell-generated forces in more physiologically relevant extracellular environments, opening new possibilities to study cell-matrix interactions.
authors.affiliation: Division of Cell and Developmental Biology, University of California, San Diego.|Department of Mechanical and Aerospace Engineeing, University of California, San Diego.
authors.forename: Begoña
authors.initials: B
authors.lastname: Álvarez-González
authors.affiliation: Department of Mechanical and Aerospace Engineeing, University of California, San Diego.
authors.forename: Shun
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Department of Mechanical and Aerospace Engineeing, University of California, San Diego.
authors.forename: Manuel
authors.initials: M
authors.lastname: Gómez-González
authors.affiliation: Division of Cell and Developmental Biology, University of California, San Diego.|Department of Mechanical and Aerospace Engineeing, University of California, San Diego.
authors.forename: Ruedi
authors.initials: R
authors.lastname: Meili
authors.affiliation: Division of Cell and Developmental Biology, University of California, San Diego.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Firtel
authors.affiliation: Department of Mechanical and Aerospace Engineeing, University of California, San Diego.|Department of Bioengineering, University of California, San Diego.|Center for Medical Devices and Instrumentation, Institute for Engineering in Medicine, University of California, San Diego.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Lasheras
authors.affiliation: Department of Mechanical and Aerospace Engineeing, University of California, San Diego.|Center for Medical Devices and Instrumentation, Institute for Engineering in Medicine, University of California, San Diego.
authors.forename: Juan C
authors.initials: JC
authors.lastname: Del Álamo
mesh_terms: D021621:Imaging, Three-Dimensional / Q000379:methods*; D018625:Microscopy, Atomic Force / Q000379:methods*; D010804:Physarum / Q000166:cytology*; D014143:Traction