Active Microrheology of Networks Composed of Semiflexible Polymers I. Computer Simulation of Magnetic Tweezers

TL;DR

This study uses computer simulations to analyze the motion of a bead in a semiflexible polymer network, revealing power-law displacement behavior, polymer pile-up effects, and force resistance mechanisms relevant to microrheology.

Contribution

It introduces a detailed simulation of bead dynamics in semiflexible networks, identifying new displacement regimes and force response characteristics.

Findings

Displacement follows a power law with two regimes: alfa=0.75 initially, then alfa=0.5.

Force response is linear and scales with polymer concentration as c^(-1.4).

Polymers pile up ahead of the bead, exerting steric repulsion.

Abstract

We have simulated the motion of a bead subjected to a constant force while embedded in a network of semiflexible polymers which can represent actin filaments. We find that the bead displacement obeys the power law x ~ t^alfa. After the initial stage characterized by the exponent alfa=0.75 we find a new regime with alfa=0.5. The response in this regime is linear in force and scales with the polymer concentration as c^(-1.4). We find that the polymers pile up ahead of the moving bead, while behind it the polymer density is reduced. We show that the force resisting the bead motion is due to steric repulsion exerted by the polymers on the front hemisphere of the bead.