Extended Data Fig. 2: Rheology and material model for collagen Batch A, B, C.

Collagen hydrogels from three different batches (a, b, c) at different concentrations of 0.6 mg/ml (purple), 1.2 mg/ml (blue), and 2.4 mg/ml (orange) are characterized using cone-plate shear-rheological measurements (top; inset shows schematic of experimental setup) and uniaxial stretch-experiments (bottom; inset shows schematic of experimental setup) as described in the Methods section of the main text. The solid lines represent the mean value and the shaded areas represent the standard error for N individual samples. Dashed lines show the fit of the finite element model to the averaged data per condition. The red axis label in c indicates different scaling compared to a, b. d, Material model parameters (Extended Data Fig. 1) for non-linear elastic biopolymers (linear stiffness k₀, the buckling coefficient d₀, the characteristic strain λs, and the stiffening coefficient ds.) for each condition. Previously measured parameters from Steinwachs et al.¹² are given for comparison. For each batch, we performed both individual fits to the data for each concentration separately, or global fits where the parameters λs, ds, and d₀ were the same for all or some of the concentrations. Global fit parameters were preferred if the fit quality was comparable to individual fits, in order to reduce the number of free fit parameters. The increased stiffness of collagen batch C compared to batch A and B is consistent with the observation of decreased cell-generated deformations (Extended Data Fig. 5). These stiffness differences can be attributed to batch-to-batch variation. Model parameters for 1.2 mg/ml collagen gels of Batch A were previously published in ref. ⁵⁸.

Source data.