Bulk and local rheology of collagen gels.

<p>(A) Bulk stress-strain rheological response of the two-layer system. For all graphs, {∘, □, △, ⊳, ◇} correspond to collagen networks with concentrations <i>c</i> = {0.25, 0.50, 0.75, 1.0, 1.5} mg/mL. (B) Average of the local stress measured at the interface with boundary stress microcopy. (C) Rescaling the data in (A) by the stress and strain values at maximum curvature <math><mrow><msubsup><mi>σ</mi><mn>0</mn><mi>R</mi></msubsup><mo>=</mo><msub><mi>σ</mi><mi>R</mi></msub><mo stretchy="false">(</mo><msubsup><mi>γ</mi><mn>0</mn><mi>R</mi></msubsup><mo stretchy="false">)</mo></mrow></math> and <math><mrow><msubsup><mi>γ</mi><mn>0</mn><mi>R</mi></msubsup></mrow></math> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118021#pone.0118021.e018" target="_blank">Eq. 3</a>) shows nearly complete data collapse for all concentrations. (D) Rescaling the data in (B) by <math><mrow><msubsup><mi>σ</mi><mn>0</mn><mi>L</mi></msubsup><mo>=</mo><msub><mi>σ</mi><mi>L</mi></msub><mo stretchy="false">(</mo><msubsup><mi>γ</mi><mn>0</mn><mi>L</mi></msubsup><mo stretchy="false">)</mo></mrow></math> and <math><mrow><msubsup><mi>γ</mi><mn>0</mn><mi>L</mi></msubsup></mrow></math> produces a similar data collapse. Scaling parameters for (C) and (D) are shown in (C, inset) and (D, inset), respectively. Error bars represent standard error from {4, 3, 4, 4, 4} trials. All lines connecting points are guides for the eye.