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Updated: May 6, 2026

The Diffusion of Passive Tracers in Laminar Shear Flow
Published on: May 1, 2018
Hydrodynamic and subdiffusive motion of tracers in a viscoelastic medium
Denis S Grebenkov1, Mahsa Vahabi, Elena Bertseva
1Laboratoire de Physique de la Matière Condensée (UMR 7643), CNRS - Ecole Polytechnique, 91128 Palaiseau, France.
We studied tracer motion in viscoelastic actin networks, finding hydrodynamic forces dominate short times and viscoelasticity at longer times. Our model explains tracer dynamics across eight orders of magnitude.
Area of Science:
- Biophysics
- Soft Matter Physics
- Cellular Mechanics
Background:
- Understanding tracer dynamics in complex biological fluids like actin networks is crucial for cellular processes.
- Viscoelastic properties of cellular environments significantly impact particle motion.
Purpose of the Study:
- To investigate the diffusive motion of micron-sized spherical tracers in viscoelastic actin filament networks.
- To analyze the transition between hydrodynamic and viscoelastic regimes across eight orders of magnitude in time.
Main Methods:
- Utilized optical-tweezers single-particle tracking to monitor tracer movement.
- Developed a minimal phenomenological model incorporating Basset and generalized Stokes forces.
Main Results:
- Hydrodynamic interactions dominate tracer motion at microsecond timescales.
- Subdiffusive scaling, characteristic of viscoelastic media, emerges at millisecond timescales.
- The derived Langevin equation successfully models inertial, hydrodynamic, subdiffusive, and optical trapping effects.
Conclusions:
- A unified model explains tracer dynamics in viscoelastic media across diverse timescales.
- Analytical formulas for mean-square displacement and velocity autocorrelation were derived.
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