Data from: Collective forces of tumor spheroids in three-dimensional biopolymer networks

We describe a method for quantifying the contractile forces that tumor
spheroids collectively exert on highly nonlinear three-dimensional
collagen networks. While three-dimensional traction force microscopy for
single cells in a nonlinear matrix is computationally complex due to the
variable cell shape, here we exploit the spherical symmetry of tumor
spheroids to derive a scale-invariant relationship between spheroid
contractility and the surrounding matrix deformations. This relationship
allows us to directly translate the magnitude of matrix deformations to
the total contractility of arbitrarily sized spheroids. We show that our
method is accurate up to strains of 50% and remains valid even for
irregularly shaped tissue samples when considering only the deformations
in the far field. Finally, we demonstrate that collective forces of tumor
spheroids reflect the contractility of individual cells for up to 1h after
seeding, while collective forces on longer timescales are guided by
mechanical feedback from the extracellular matrix.