Figure 2:

Effect of a group of contracting inclusions on stiffness at the scale of a cell. (a) A representative undeformed state of the matrix containing a cluster of inclusions. The inclusions had a diameter of D = 2L_f and were randomly embedded inside the matrix at an average inter-inclusion spacing of ≈ 1.5L_f. (b) After inclusions contracted by 40%, the network globally contracted (uncontracted matrix size shown by the dashed box). Force transmission is shown by force chains constituting the top 20% highly stretched fibers in the matrix (red). These force chains emanated radially from the periphery of the inclusions. (c, d) The deformed matrix (of panel b) with a contracting dipole in the inter-inclusion space as depicted by the black line. Panels c and d depict two different representative orientations of the dipole. Insets depict the enlarged views of the respective dipole. The fibers of the deformed matrix are color coded based on the normalized values of their excess lengths (ξ/L_f). The dipoles contracted and registered the stiffness of the matrix inside the inter-inclusion space. (e) For differently aligned dipoles and for six independent matrices, the ratio of the values of matrix stiffness sensed by the dipole after and before the contraction of inclusions (k_s/k_s,ref) were recorded. k_s/k_s,ref < 1 indicates matrix softening due to contracting inclusions. Each marker indicates a different dipole; each marker shape indicates a different independent fiber network.