Figure 1.

Shear bulk rheology was used to probe the mechanical properties of actin networks. (A) Cartoon representation of a sample undergoing a shear deformation. The shear stress is the force (F) per cross-sectional area of the sample, whereas the strain is the unitless shear displacement of the sample. (B) Representative stress-strain curve and differential elastic modulus, $K^{\text{'}}=\partial \sigma /\partial \gamma$ (the slope of the stress-strain curve), of a fully percolated actin network with a twofold molar excess of calponin. Under a shear deformation, the network exhibited three mechanical regimes. In the linear regime (I), the network responded as a linear spring with a constant differential elastic modulus. Upon reaching a critical strain, ${\gamma }_{crit}$, the elasticity of the material increased with strain, termed strain stiffening (II). After reaching a maximum elastic modulus, the network entered a failure regime (III) and strain weakened as it began breaking, eventually reaching a yield stress, ${\sigma }_{max}$, and yield strain, ${\gamma }_{max}$.