Actin filament alignment causes mechanical hysteresis in cross-linked networks

Area of Science:

• Biophysics
• Cell Biology
• Materials Science

Background:

• Cells dynamically regulate their mechanical properties by remodeling the actin cytoskeleton, a complex network of actin filaments.
• In vitro reconstituted actin networks serve as a model system to study the mechanisms of cytoskeletal mechanical adaptation.
• Applied shear stress can induce adaptive behavior and nonlinear elasticity asymmetry in these reconstituted networks.

Purpose of the Study:

• To investigate how tuning the concentration and mechanical properties of cross-linking proteins affects mechanical hysteresis in actin networks.
• To identify the key conditions necessary for observing adaptive mechanical responses in the actin cytoskeleton.
• To understand the relationship between cross-linker characteristics and the emergent mechanical properties of actin networks.

Main Methods:

• Experimental reconstitution of actin filament networks in vitro.
• Computational simulations of actin networks with varying cross-linker properties.
• Application of shear stress for network training and analysis of nonlinear elasticity and hysteresis.

Main Results:

• Mechanical hysteresis is dependent on initial nonlinear strain stiffening and filament reorientation during training.
• Hysteresis exhibits a non-monotonic dependence on cross-linker concentration, peaking at moderate levels.
• Longer or more flexible cross-linkers enhance hysteresis, and a universal relationship exists between hysteresis and filament alignment.

Conclusions:

• Cross-linker concentration and properties are critical regulators of mechanical adaptation in actin networks.
• Filament reorientation and nonlinear strain stiffening are essential for observing significant mechanical hysteresis.
• The findings provide fundamental insights into the design principles governing the mechanical adaptability of biological materials.