Filament Nucleation Tunes Mechanical Memory in Active Polymer Networks

Area of Science:

• Biomaterials Science
• Cellular Biophysics
• Polymer Physics

Background:

• The F-actin cytoskeleton is a dynamic polymer network essential for cell mechanics and shape.
• Understanding how active polymer networks grow and remodel is crucial for designing functional materials.

Purpose of the Study:

• To investigate the role of F-actin nucleation in regulating mechanical energy and material properties.
• To explore how varying nucleation density affects the formation of topological defects and shape memory in biomimetic cytoskeletons.

Main Methods:

• Constructed a biomimetic model of the cytoskeleton using purified F-actin.
• Varied the extent of F-actin nucleation from a membrane surface.
• Analyzed polymerization-induced bending energy, material relaxation, and filament assembly dynamics.

Main Results:

• Low and high F-actin nucleation resulted in isotropic materials with low, relaxed bending energies.
• Intermediate nucleation led to a 100-fold increase in internal energy due to unrelaxed stresses.
• High filament curvatures at critical nucleation templated further assembly, forming stable, vortex-like topological defects.

Conclusions:

• F-actin nucleation acts as a critical control point for mechanical energy accumulation and dissipation.
• Intermediate nucleation densities are essential for generating and stabilizing topological defects in active materials.
• This mechanism allows active materials to encode shape memory by coordinating mechanical and chemical timescales.