Rapid local compression in active gels is caused by nonlinear network response.

Area of Science:

• Cellular mechanics
• Biophysics
• Cytoskeletal dynamics

Background:

• The actin cytoskeleton and myosin motors are crucial for cellular processes.
• Cytoskeletal filaments exhibit nonlinear responses to motor activity.

Purpose of the Study:

• Investigate mechanics and force generation in a model actin cytoskeleton reconstituted in vitro.
• Analyze the response and fluctuations of embedded probe particles to understand cytoskeletal behavior.

Main Methods:

• Reconstitution of an in vitro actin cytoskeleton model.
• Observation of micron-scale probe particle response and fluctuations.
• Modeling myosin mini-filaments as force dipoles.

Main Results:

• Anomalously correlated probe fluctuations indicate rapid local network compression/draining.
• Observed nonlinear response beyond ordinary linear shear elasticity.
• Anomalous compression propagation is consistent with motor-induced gel stiffening.

Conclusions:

• Actin networks display complex nonlinear mechanics driven by myosin motors.
• Microscopic forces lead to emergent behaviors like anomalous compression.
• This nonlinear response is key to understanding large-scale cytoskeletal organization and function.