Tuning the nature of mechano-memory in actin networks

To adapt to external stimuli, cells can dynamically alter their material properties through rearrangement of the actin cytoskeleton, a cross-linked network of actin filaments. In addition to its importance in cell biology, understanding this mechanical response provides strategies for creation of novel materials. A recent study demonstrated that applied shear stress can encode mechanical memory in these networks, characterized by an anisotropic response under subsequent shear deformations. The network becomes stiffer in the direction of the previously applied stress. Here, we vary both the cross-linker concentration and stiffness to examine the effect of network architecture on this mechano-memory. While networks cross-linked with intermediate concentrations of cross-linkers both stiffen in the direction of the previously applied stress and weaken in the opposite direction, networks with high cross-linker concentrations only weaken. Remarkably, this effect is independent of cross-linker type and rigidity. Overall, our study is crucial for understanding the process by which networks rearrange under external stress and the resulting effect on response to shear.