Figure 1:

Experiments and simulations characterizing the global modulus of fibrous matrix with contracting inclusions. (a) Diagram of experiments with the rheometer. A collagen matrix with embedded PNIPAAm microspheres was polymerized between the two coverslips attached to the parallel plates of the rheometer, and the top plate was axially rotated to twist the sample. (b) Small strain shear modulus (G₀) of nine independent PNIPAAm-embedded matrices measured before and after the contraction of embedded PNIPAAm microspheres, respectively at temperatures 22°C and 39°C. The increase in the shear modulus from 22°C to 39°C is statistically significant (p = 0.0039, sign test). (c) Small strain shear modulus (G₀) of eight independent control collagen matrices at temperatures 22°C and 39°C. The temperature change had no significant effect on the modulus (p = 1, sign test). (d) Simulation on an equivalent 2D matrix model with multiple inclusions and simple shear boundary conditions. Prior to the contraction of these inclusions, the shear modulus at 0.5% shear strain was quantified and defined as G₁. (e) The deformed model after the contraction of inclusions by 40%, with the shear modulus at 0.5% shear strain called G₂. (f) Ratios G₂/G₁ for six independent models were always greater than unity, indicating global stiffening of the matrix due to contracted inclusions.