The confined Generalized Stokes-Einstein relation and its consequence on intracellular two-point microrheology

Area of Science:

• Soft Matter Physics
• Fluid Dynamics
• Materials Science

Background:

• Two-point microrheology (TPM) infers complex fluid properties from probe motion.
• Current TPM theory is limited to unconfined media.
• Confinement effects in biological cells and droplets necessitate new theoretical approaches.

Purpose of the Study:

• To develop and validate a new microrheology theory for confined complex fluids.
• To investigate the impact of confinement on probe dynamics and material properties.
• To establish a theoretical framework applicable to various confinement scenarios.

Main Methods:

• Confined Stokesian Dynamics simulations were employed.
• Explicit representation of many-body hydrodynamic couplings between colloids and cavity.
• Simulations covered arbitrary colloid concentrations and cavity sizes.

Main Results:

• Established theory breaks down under confinement.
• Developed a Confined Generalized Stokes-Einstein Relation.
• Confinement increases viscosity and alters particle dynamics via hydrodynamic and entropic coupling.
• New theory yields a master curve across conditions.
• Model is essential for colloids larger than 0.005 times enclosure size.

Conclusions:

• The developed theory accurately describes microrheology in confined complex fluids.
• Confinement significantly influences material properties and probe behavior.
• The new model provides a universal framework for confined microrheology studies.